Chemistry Class X Past Paper 2017-18 PDF

CHEMISTRY REFERENCE STUDY MATERIAL for CLASS – X 2017 – 18 CHAPTER WISE CONCEPTS, FORMULAS AND QUESTIONS INLCUDING HOTS QUESTIONS Prepared by...

CHEMISTRY REFERENCE STUDY MATERIAL for CLASS – X 2017 – 18 CHAPTER WISE CONCEPTS, FORMULAS AND QUESTIONS INLCUDING HOTS QUESTIONS Prepared by M. S. KUMARSWAMY, TGT(MATHS) M. Sc. Gold Medallist (Elect.), B. Ed. Kendriya Vidyalaya gachibowli Prepared by: M. S. KumarSwamy, TGT(Maths) Page - A -  PREFACE It gives me great pleasure in presenting the Reference Study Material in Chemistry for Class X Board Examination 2018. It is in accordance with the syllabus of the session 2017–18 as per CBSE guidelines. Each chapter has a large number of questions along with all concepts and descriptions of topics in such a simple style that even the weak students will be able to understand the topic very easily. The most important feature of this material is that NCERT book questions(intext questions) and exercises included along with answers. Keeping the mind the mental level of a child, every effort has been made to introduce simple questions in starting before HOTS questions so that the child solve them easily and gets confidence. I avail this opportunity to convey my sincere thanks to respected sir, Shri U. N. Khaware, Additional Commissioner(Acad), KVS Headquarter, New Delhi, respected sir, Shri S. Vijay Kumar, Joint Commissioner(Admn), KVS Headquarter, New Delhi, respected sir Shri P. V. Sairanga Rao, Deputy Commissioner(Acad), KVS Headquarter, New Delhi, respected sir Shri. D. Manivannan, Deputy Commissioner, KVS RO Hyderabad, respected sir Shri Isampal, Deputy Commissioner, KVS RO Bhopal, respected sir Shri Jagdish Mohan Rawat, Director, KVS ZIET Chandigarh, respected sir Shri P. Deva Kumar, Deputy Commissioner, KVS RO Bangalore, respected sir Shri Nagendra Goyal, Deputy Commissioner, KVS RO Ranchi, respected sir Shri Y. Arun Kumar, Deputy Commissioner, KVS RO Agra,, respected sir Shri Sirimala Sambanna, Assistant Commissioner, KVS RO Jammu, respected sir Shri. K. L. Nagaraju, Retd-AC, KVS RO Bangalore and respected sir Shri M.K. Kulshreshtha, Retd-AC, KVS RO Chandigarh for their blessings, motivation and encouragement in bringing out this project in such an excellent form. I also extend my special thanks to respected sir Shri. P. S. Raju, Principal, KV Gachibowli, respected madam Smt. Nirmala Kumari M., Principal, KV Mysore & respected sir Shri. M. Vishwanatham, Principal, KV Raichur for their kind suggestions and motivation while preparing this Question Bank. I would like to place on record my thanks to respected sir Shri. P. K. Chandran, Principal, presently working in KV Bambolim. I have started my career in KVS under his guidance, suggestions and motivation. Inspite of my best efforts to make this notes error free, some errors might have gone unnoticed. I shall be grateful to the students and teacher if the same are brought to my notice. You may send your valuable suggestions, feedback or queries through email to [email protected] that would be verified by me and the corrections would be incorporated in the next year Question Bank. M. S. KUMARSWAMY Prepared by: M. S. KumarSwamy, TGT(Maths) Page - B - Prepared by: M. S. KumarSwamy, TGT(Maths) Page - C -  DEDICATED TO MY FATHER LATE SHRI. M. S. MALLAYYA Prepared by: M. S. KumarSwamy, TGT(Maths) Page - D -  CHAPTER – 1 CHEMICAL REACTIONS AND EQUATIONS CHEMICAL REACTIONS Any change can be classified as physical change and chemical change. Physical changes can be easily reversed but, it is not easy to reverse a chemical change. In chemical changes, new substances are formed and it is difficult to regenerate the original substances. Chemical changes are more permanent than physical changes. Chemical reaction involves chemical changes. Chemical reactions are the processes in which new substances with new properties are formed. During a chemical reaction, atoms of one element do not change into those of another element. Only a rearrangement of atoms takes place in a chemical reaction. Magnesium ribbon burns with a dazzling white flame and changes into a white powder. This powder is magnesium oxide. It is formed due to the reaction between magnesium and oxygen present in the air. Magnesium Oxygen Magnesium Oxide   Heat (As ribbon) (From air) (White powder) The burning of magnesium in air to form magnesium oxide is an example of chemical reaction. REACTANTS AND PRODUCTS The substances which take part in a chemical reaction are called reactants. The new substances produced as a result of chemical reaction are called products. In the above chemical reaction, there are two reactants : Magnesium and Oxygen but only one product : Magnesium oxide. CHARACTERISTICS OF CHEMICAL REACTIONS In a chemical reaction, reactants are transformed into products. The important characteristics of chemical reaction are: Evolution of a gas Formation of a precipitate Change in colour Change in temperature and Change in state. Any one of these characteristics can tell us whether a chemical reaction has taken place or not. CHEMICAL EQUATIONS The method of representing a chemical reaction with the help of symbols and formulas of the substances involved in it is known as chemical equation. A word-equation shows change of reactants to products through an arrow placed between them. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them. Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them. The arrowhead points towards the products, and shows the direction of the reaction. Example: A + B → C + D In this equation, A and B are called reactants and C and D are called the products. Arrow shows the direction of chemical reaction. Condition, if any, is written generally above the arrow. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 1 - When hydrogen reacts with oxygen, it gives water. This reaction can be represented by following chemical equation: Hydrogen + Oxygen ⇨ Water H2 + O2 → H2O In first equation words are used and in second symbols of substances are used to write the chemical equation. For convenience, symbol of substance is used to represent chemical equations. Chemical Equation is a way to represent the chemical reaction in concise and informative way. Chemical equation can be divided into two types – Balanced Chemical Equation and Unbalanced Chemical Equation. Balanced Chemical Equation: A balanced chemical equation has number of atoms of each element equal on both sides. Example: Zn + H2SO4 → ZnSO4 + H2 In this equation, numbers of zinc, hydrogen and sulphate are equal on both sides, so it is a balanced chemical equation. Unbalanced Chemical Equation: If the number of atoms of each element in reactants is not equal to the number of atoms of each element present in product, then the chemical equation is called unbalanced chemical equation. Example: Fe + H2O → Fe3O4 + H2 In this example number atoms of elements are not equal on two sides of the reaction. For example, on the left hand side only one iron atom is present, while three iron atoms are present on the right hand side. Therefore, it is an unbalanced chemical equation. BALANCING A CHEMICAL EQUATION: To balance the given or any chemical equation, follow these steps: Fe + H2O → Fe3O4 + H2 Write the number of atoms of elements present in reactants and in products in a table; as shown here. Name of atom No. of atoms in reactant No. of atoms in product Iron 1 3 Hydrogen 2 2 Oxygen 1 4 Balance the atom which is the maximum in number; on either side of chemical equation. In this equation, the number of oxygen atom is the maximum on the RHS. To balance the oxygen one needs to multiply the oxygen on the LHS by 4; so that the number of oxygen atoms becomes equal on both sides. Fe + 4 x H2O → Fe3O4 + H2 Now, the number of hydrogen atoms becomes 8 on the LHS; which is more than that on the RHS. To balance it, one needs to multiply the hydrogen on the RHS by 4. Fe + 4 x H2O → Fe3O4 + 4 x H2 After that number of oxygen and hydrogen atoms becomes equal on both sides. The number of iron is one on the LHS, while it is three on the RHS. To balance it, multiply the iron on the LHS by 3. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 2 -  3 x Fe + 4 x H2O → Fe3O4 + 4 x H2 Now the number of atoms of each element becomes equal on both sides. Thus, this equation becomes a balanced equation. Name of atom No. of atoms in reactant No. of atoms in product Iron 3 3 Hydrogen 8 8 Oxygen 4 4 After balancing, the above equation can be written as follows. 3Fe + 4H2O → Fe3O4 + 4H2 Writing the symbols of Physical States of substances in Chemical equation: By writing the physical states of substances a chemical equation becomes more informative.  Gaseous state is represented by symbol ‘g’  Liquid state is represented by symbol ‘l’  Solid state is written by symbol ‘s’  Aqueous solution is written by symbol ‘aq’ Writing the condition in which reaction takes place: The condition is generally written above and/or below the arrow of a chemical equation. Thus, by writing the symbols of physical state of substances and condition under which reaction takes place, a chemical equation can be made more informative. INTEXT QUESTIONS PAGE NO. 6 Q1: Why should a magnesium ribbon be cleaned before it is burnt in air? Answer : Magnesium is an extremely reactive metal. When stored, it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper for removing this layer so that the underlying metal can be exposed to air. Question 2: Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen Answer : Question 3: Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water. Answer : Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 3 - TYPES OF CHEMICAL REACTION Chemical reactions can be classified in following types:  Combination Reaction  Decomposition Reaction  Displacement Reaction  Double Displacement Reaction  Oxidation and Reduction Reaction COMBINATION REACTION Reactions in which two or more reactants combine to form one product are called COMBINATION REACTION. A general combination reaction can be represented by the chemical equation given here. Example: When magnesium is burnt in air (oxygen), magnesium oxide is formed. In this reaction, magnesium is combined with oxygen. Mg + O2 → 2MgO Magnesium + Oxygen ⇨ Magnesium oxide When carbon is burnt in oxygen (air), carbon dioxide is formed. In this reaction, carbon is combined with oxygen. C + O2 → CO2 Carbon + Oxygen ⇨ Carbon dioxide When hydrogen reacts with chlorine, hydrogen chloride is formed. H2 + Cl2 → 2HCl Hydrogen + Chlorine ⇨ Hydrogen chloride When calcium oxide reacts with water, calcium hydroxide is formed CaO + H2O → Ca(OH)2 Calcium oxide + Water → Calcium hydroxide When carbon monoxide reacts with oxygen, carbon dioxide is formed. 2CO + O2 → 2CO2 Carbon monoxide + Oxygen → Carbon dioxide DECOMPOSITION REACTION Reactions in which one compound decomposes in two or more compounds or element are known as DECOMPOSITION REACTION. Decomposition reaction is just opposite of combination reaction. A general decomposition reaction can be represented as follows: Example: When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide CaCO3 → CaO + CO2 Calcium carbonate → Calcium oxide + Carbon dioxide Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 4 - When ferric hydroxide is heated, it decomposes into ferric oxide and water 2Fe(OH)3 → Fe2O3 + 3H2O Ferric hydroxide → Ferric oxide + Water When lead nitrate is heated, it decomposes into lead oxide, nitrogen dioxide and oxygen. 2Pb(NO3)2 → 2PbO + 4NO2 + O2 Lead nitrate ⇨ Lead oxide + Nitrogen oxide + Oxygen In above examples, compound is decomposed because of heating, so, these reactions are called THERMAL DECOMPOSITION REACTION. ELECTROLYTIC DECOMPOSITION Reactions in which compounds decompose into simpler compounds because of passing of electricity, are known as ELECTROLYTIC DECOMPOSITION. This is also known as ELECTROLYSIS. Example: When electricity is passed in water, it decomposes into hydrogen and oxygen. 2H2O → 2H2 + O2 PHOTOLYSIS OR PHOTO DECOMPOSITION REACTION Reactions in which a compound decomposes because of sunlight are known as PHOTOLYSIS or PHOTO DECOMPOSITION REACTION. Example: When silver chloride is put in sunlight, it decomposes into silver metal and chlorine gas. 2AgCl → 2Ag + Cl2 Similarly, when silver bromide is put under sunlight, it decomposes into silver metal and bromine gas. 2AgBr → 2Ag + Br2 Photographic paper has coat of silver chloride, which turns into grey when exposed to sunlight. It happens because silver chloride is colourless while silver is a grey metal. INTEXT QUESTIONS PAGE NO. 10 Question 1: A solution of a substance ‘X’ is used for white washing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water. Answer : (i) The substance ‘X’ is calcium oxide. Its chemical formula is CaO. (ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime). Question 2: Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas. Answer : Water (H2O) contains two parts hydrogen and one part oxygen. Therefore, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During electrolysis, since hydrogen goes to one test tube and oxygen goes to another, the amount of gas collected in one of the test tubes is double of the amount collected in the other. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 5 - DISPLACEMENT REACTION Reactions in which atoms or ions move from one compound to other to form new compound are known as DISPLACEMENT REACTION. Displacement reaction is also known as Substitution Reaction or Single displacement /Replacement Reaction. A general displacement reaction can be represented using chemical equation as follows: Displacement reaction takes place only when ‘A’ is more reactive than B. If ‘B’ is more reactive than ‘A’, then ‘A’ will not displace ‘C’ from ‘BC’ and reaction will not be taken place. Example: When zinc reacts with hydrochloric acid, it gives hydrogen gas and zinc chloride. Zn + 2HCl → ZnCl2 + H2 When zinc reacts with copper sulphate, it forms zinc sulphate and copper metal. Zn + CuSO4 → ZnSO4 + Cu When silver metal is dipped in copper nitrate, no reaction takes place because silver metal is less reactive than copper. Ag + Cu(NO3 )2 → No reaction takes place DOUBLE DISPLACEMENT REACTION Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions. Example: When solution of barium chloride reacts with the solution of sodium sulphate, white precipitate of barium sulphate is formed along with sodium chloride. BaCl2 + Na2SO4 → BaSO4 + 2NaCl When sodium hydroxide (a base) reacts with hydrochloric acid, sodium chloride and water are formed. NaOH + HCl → NaCl + H2O Double displacement reaction, in which precipitate is formed, is also known as precipitation reaction. Neutralisation reactions are also examples of double displacement reaction. EXOTHERMIC AND ENDOTHERMIC REACTION The chemical reactions which proceed with the evolution of heat energy are called exothermic reactions. N2 + 3H2 → 2NH3 + Heat All combustion reactions are exothermic. Heat energy is liberated as the reaction proceeds. The chemical reactions which proceed with the absorption of heat energy are called endothermic reactions. Most of the combination reactions are endothermic. Most of the decomposition reactions are exothermic. Respiration is a decomposition reaction in which energy is released. When quick lime (calcium carbonate) is added to water, it decomposes and releases energy. Cooking involves chemical reactions which are endothermic as cooking is possible because of heating. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 6 - OXIDATION AND REDUCTION REACTION: Oxidation: Addition of oxygen or non-metallic element or removal of hydrogen or metallic element from a compound is known as oxidation. Elements or compounds in which oxygen or non-metallic element is added or hydrogen or metallic element is removed are called to be oxidized. Oxidizing agent: Compounds which can add oxygen or a non-metallic compound or remove hydrogen or metallic element are known as oxidizing agents. Reduction: Addition of hydrogen or metallic element or removal of oxygen or non-metallic element from a compound is called reduction. The compound or element which goes under reduction is called to be reduced. Reducing agent: Compounds or elements which can cause reduction are called reducing agents. In a chemical reaction oxidation and reduction both take place simultaneously and such reactions are also known as REDOX REACTIONS. In the word REDOX, ‘Red’ stands for reduction and ‘Ox’ stands for oxidation. Example: When iron reacts with air, it forms iron oxide (rust) 4Fe + 3O2 → 2Fe2O3 In this reaction, oxygen is added to iron, thus, iron is oxidized. Here oxygen is oxidizing agent. When cupric oxide reacts with hydrogen, it gives copper and water. CuO + H2 → Cu + H2O In this reaction, oxygen is removed from copper and oxygen is added to hydrogen. So, cupric oxide is reduced to copper and hydrogen is oxidized to water. Cupric oxide is oxidizing agent and hydrogen is reducing agent. When sodium hydroxide reacts with hydrochloric acid, it gives sodium chloride and water. NaOH + HCl → NaCl + H2O In this reaction, sodium hydroxide is reduced to sodium chloride since hydrogen is removed from sodium hydroxide. Hydrochloric acid is oxidized to water, since oxygen is added to hydrogen chloride and non-metallic element chloride is removed. Sodium hydroxide is oxidising agent and hydrochloric acid is reducing agent. In this reaction oxidation and reduction both takes place simultaneously, thus it is an example of redox reaction. SIGNIFICANCE OF OXIDATION REDUCTION IN EVERYDAY LIFE:  Respiration is oxidation reaction in which food is oxidized to produce energy.  Iron gets oxidized to form rust; which leads to corrosion of iron in the long run.  Most of the metals react with atmospheric oxygen and it leads to formation of a layer on the metal article. The metal gets corroded in the long run.  Rusting of iron can be prevented by painting the iron article. This can also be prevented by applying a layer of zinc over iron article. This process is known as galvanization.  Fried food gets oxidized when exposed to air. This spoils the taste of the food and the food becomes unfit for consumption. The spoiling of fried food because of oxidation is called rancidity. Fried food is often packed in airtight packets to prevent rancidity. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 7 -   We are able to utilize various types of fuel because of oxidation. Oxidation of fuel helps in producing energy. CORROSION Corrosion is defined as the slow and steady destruction of a metal by the environment. It results in the deterioration of the metal to form metal compounds by means of chemical reactions with the environment. Corrosion is a simple electro chemical reaction. When the surface of iron is in contact with moisture and other gases in the atmosphere an electrochemical reaction occurs. In this, impure iron surface acts as the cathode and pure iron acts as anode. H2CO3 formed from moisture and CO2 from air acts as electrolyte. The electrochemical reactions are as follows: Fe → Fe2+ + 2e– O2 + 2H2O + 4e– → 4OH– The Fe ions are oxidised to Fe3+ ions. 2+ The Fe3+ ions combine with OH– ions to form Fe(OH)3.This becomes rust (Fe2O3.xH2O) which is hydrated ferric oxide. METHODS OF PREVENTING CORROSION Corrosion of metals is prevented by not allowing them to come in contact with moisture,CO2 and O2.This is achieved by the following methods: By coating with paints: Paint coated metal surfaces keep out air and moisture. By coating with oil and grease: Application of oil and grease on the surface of iron tools prevents them from moisture and air. By alloying with other metals: Alloyed metal is more resistant to corrosion. Example: stainless steel. By the process of galvanization: This is a process of coating zinc on iron sheets by using electric current. In this zinc forms a protective layer of zinc carbonate on the surface of iron. This prevents corrosion. Electroplating: It is a method of coating one metal with another by passing electric current. Example: silver plating, nickel plating. This method not only lends protection but also enhances the metallic appearance. Sacrificial protection: Magnesium is more reactive than iron. When it is coated on the articles made of steel it sacrifices itself to protect the steel. RANCIDITY When fats and oils are oxidised, they become rancid and their smell and taste change. Rancidity is the chemical decomposition of fats, oils and other lipids. There are three basic types of rancidity. Hydrolytic rancidity occurs when water splits fatty acid chains away from the glycerol backbone in glycerides. Oxidative rancidity occurs when the double bonds of an unsaturated fatty acid react chemically with oxygen. Microbial rancidity refers to a process in which microorganisms such as bacteria use their enzymes, including lipases, to break down chemical structures in the fat. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 8 - In each case, these chemical reactions result in undesirable odors and flavors. it is a condition produced by aerial oxidation of unsaturated fat present in foods and other products, marked by unpleasant odour or flavour. When a fatty substance is exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours. Butter becomes rancid by the foregoing process and by hydrolysis, which liberates volatile and malodorous acids, particularly butyric acid. Saturated fats such as beef tallow are resistant to oxidation and seldom become rancid at ordinary temperatures. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Rancidity can be avoided by: 1. Storing food in air tight containers 2. Storing food in refrigerators 3. Adding antioxidants 4. Storing food in an environment of nitrogen INTEXT QUESTIONS PAGE NO. 13 Question 1: Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Answer : When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper sulphate solution forming iron sulphate, which is green in colour. Therefore, the blue colour of copper sulphate solution fades and green colour appears. Question 2: Give an example of a double displacement reaction other than the one given in Activity 1.10. Answer : Sodium carbonate reacts with calcium chloride to form calcium carbonate and sodium chloride. In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence, it is a double displacement reaction. Question 3: Identify the substances that are oxidised and the substances that are reduced in the following reactions. Answer : (i) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 9 - (ii) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H2O). EXERCISE QUESTIONS PAGE NO. 14, 15 and 16 Question 1: Which of the statements about the reaction below are incorrect? (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced. (i) (a) and (b) (ii) (a) and (c) (iii) (a), (b) and (c) (iv) all Answer : (i)(a) and (b) Question 2: The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction. Answer : (d) The given reaction is an example of a displacement reaction. Question 3: What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer. (a) Hydrogen gas and iron chloride are produced. (b) Chlorine gas and iron hydroxide are produced. (c) No reaction takes place. (d) Iron salt and water are produced. Answer : (a) Hydrogen gas and iron chloride are produced. The reaction is as follows: Question 4: What is a balanced chemical equation? Why should chemical equations be balanced? Answer : A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation. The law of conservation of mass states that mass can neither be created nor destroyed. Hence, in a chemical reaction, the total mass of reactants should be equal to the total mass of the products. It means that the total number of atoms of each element should be equal on both sides of a chemical equation. Hence, it is for this reason that chemical equations should be balanced. Question 5: Translate the following statements into chemical equations and then balance them. (a) Hydrogen gas combines with nitrogen to form ammonia. (b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide. (c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. (d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 10 - Answer : Question 6: Balance the following chemical equations. Answer : Question 7: Write the balanced chemical equations for the following reactions. (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water (b) Zinc + Silver nitrate → Zinc nitrate + Silver (c) Aluminium + Copper chloride → Aluminium chloride + Copper (d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride Answer : Question 8: Write the balanced chemical equation for the following and identify the type of reaction in each case. (a)Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s) (b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g) (c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g) (d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g) Answer : Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 11 - Question 9: What does one mean by exothermic and endothermic reactions? Give examples. Answer : Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions. Example: Mixture of sodium and chlorine to yield table salt In other words, combination reactions are exothermic. Reactions that absorb energy or require energy in order to proceed are called endothermic reactions. For example: In the process of photosynthesis, plants use the energy from the sun to convert carbon dioxide and water to glucose and oxygen. Question 10: Why is respiration considered an exothermic reaction? Explain. Answer : Energy is required to support life. Energy in our body is obtained from the food we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose combines with oxygen in the cells and provides energy. The special name of this combustion reaction is respiration. Since energy is released in the whole process, it is an exothermic process. Question 11: Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions. Answer : Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy. Question 12: Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity. Answer : (a) Thermal decomposition: (b) Decomposition by light: Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 12 - (c) Decomposition by electricity: Question 13: What is the difference between displacement and double displacement reactions? Write equations for these reactions. Answer : In a displacement reaction, a more reactive element replaces a less reactive element from a compound. where A is more reactive than B In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds. For example: Displacement reaction: Double displacement reaction: Question 14: In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved. Answer : Question 15: What do you mean by a precipitation reaction? Explain by giving examples. Answer : A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction. For example: In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction. Another example of precipitation reaction is: In this reaction, barium sulphate is obtained as a precipitate. Question 16: Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction Answer : (a) Oxidation is the gain of oxygen. For example: Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 13 - In equation (i), H2 is oxidized to H2O and in equation (ii), Cu is oxidised to CuO. (b) Reduction is the loss of oxygen. For example: In equation (i), CO2 is reduced to CO and in equation (ii), CuO is reduced to Cu. Question 17: A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed. Answer : ‘X’ is copper (Cu) and the black-coloured compound formed is copper oxide (CuO). The equation of the reaction involved on heating copper is given below. Question 18: Why do we apply paint on iron articles? Answer : Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented. So presence of air and moisture is essential for rusting to take place. Question 19: Oil and fat containing food items are flushed with nitrogen. Why? Answer : Nitrogen is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided. Question 20: Explain the following terms with one example each. (a) Corrosion (b) Rancidity Answer : (a) Corrosion: Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc. For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide. This hydrated iron oxide is rust. (b) Rancidity: The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity. For example, the taste and smell of butter changes when kept for long. Rancidity can be avoided by: 1. Storing food in air tight containers 2. Storing food in refrigerators 3. Adding antioxidants 4. Storing food in an environment of nitrogen Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 14 -  ASSIGNMENT QUESTIONS SET – 1 CHAPTER – 1 CHEMICAL REACTIONS AND EQUATIONS VERY SHORT ANSWER TYPE QUESTIONS 1. How are chemical reactions expressed in the shortest way? 2. What is the type of reaction in which the reactant gives simpler products? 3. What is the type of reaction in which two or more reactants combine to a give a single product? 4. In which type of reaction does an exchange of partners take place? 5. Why are chemical equations balanced? 6. What symbol is used to indicate a solution made in water? 7. What type of reaction does occur during the digestion of food inside our body? 8. What type of reaction is represented by the following equation? CaCO3 → CaO + CO2 9. What type of reaction does occur when silver bromide is exposed to sunlight? 10. A solution of a substance is used for white-washing. Name the substance with its formula. 11. Name the type of reaction which is represented by the following equations: Fe2O3 + 2Al → Al2O3 + 2Fe 12. Balance the following equation using state symbols: Fe + HCl → FeCl2 + H2. 13. Express the following statement in the form of a balanced chemical equation: “Sodium reacts with water to form sodium hydroxide and hydrogen”. 14. Write the balanced chemical equation for the reaction that occurs between aluminium hydroxide and sulphuric acid forming aluminium sulphate and water. 15. What type of reaction does occur when ammonia is allowed to react with hydrogen chloride? 16. Name the type of reaction involved when a zinc plate is dipped in a solution of copper sulphate? 17. In the reaction, CuO(s) + H2(g) → Cu(s) + H2O(l). Pick out the following: (i) the substance which is oxidised (ii) the substance which is reduced (iii) the oxidizing agent (iv) the reducing agent Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 15 - 18. What chemical reaction is involved in the corrosion of iron? 19. Aluminum metal when burnt in air forms aluminium oxide. Write the balanced chemical equation for the reaction. 20. Is the reaction represented by the following reaction a displacement reaction? 2KI + Cl2 → 2KCl + I2 21. Express the following reaction in the form of a balanced chemical equation: “When a strip of copper is dipped in a solution of silver nitrate, silver metal is precipitated and a solution of copper nitrate is produced.” 22. Write the following equation in a balanced form? NH3 + O2 → N2 + 2H2O 23. What is the process called in which a substance is converted into a new substance? 24. Name the gas evolved when a magnesium ribbon is dropped into dilute sulphuric acid? 25. Give an example of a double displacement reaction. 26. Is copper more reactive than iron? Give the equation of the reaction in support of your answer? 27. Can a combustion reaction be a redox reaction? 28. Can a double displacement reaction be a redox reaction? 29. State one characteristics of the chemical reaction when lemon juice is added gradually to potassium permanganate solution? 30. Which gas does evolve when dilute HCl is added to sodium carbonate? 31. Why is photochemical reaction considered an endothermic reaction? 32. Which term is applied for the process in which unpleasant smell and taste develop in foods containing fats and oils? 33. What are the substances called which are added to foods containing fats and oils to protect them from becoming rancid? 34. Why are potato chips packaged in nitrogen? 35. In the refining of silver, silver is obtained from silver nitrate by using copper metal. Write down the reaction involved? 36. A shiny brown coloured element when heated in air becomes black. Name the element and the black coloured substance so formed. 37. Name the substance which is oxidised in the following reaction: H2S + Cl2 → 2HCl + S 38. Why are all decomposition reactions endothermic? 39. Is the decomposition of vegetable matter into compost an exothermic reaction? Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 16 - 40. Why is photosynthesis an endothermic reaction? 41. Balance the following equation: (i) MNO2 + HCl → MNCl2 + Cl2 + H2O (ii) Na + O2 → Na2O (iii) H2O2 → H2O + O2 (iv) Mg(OH)2 + HCl → MgCl2 + H2O (v) Fe + O2 → Fe2O3 (vi) Al(OH)3 → Al2O3 + H2O (vii) NH3 + CuO → Cu + N2 + H2O (viii) Al2(SO4)3 + NaOH → Al(OH)3 + Na2SO4 (ix) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O (x) NaOH + H2SO4 → Na2SO4 + H2O (xi) BaCl2 + H2SO4 → BaSO4 + HCl (xii) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water (xiii) Aluminium + Copper chloride → Aluminium chloride + Copper (xiv) Calcium + Water → Calcium hydroxide + Hydrogen (xv) Sulphur dioxide + Oxygen → Sulphur trioxide (xvi) MnO2 + HCl → MnCl2 + Cl2 + H2O (xvii) Zn + HCl → ZnCl2 SHORT ANSWER TYPE QUESTIONS 1. What do you mean by a Chemical reaction? Give an example of a chemical reaction. 2. What do you mean by a combination reaction? Give an example. 3. What do you mean by a displacement reaction? Give an example. 4. What do you mean by a decomposition reaction? Give an example. 5. What do you mean by a double displacement reaction? Give an example. 6. Explain the term “Electrolytic decomposition”, giving a suitable example. 7. Mention any two uses of decomposition reaction. 8. Give an example of a reaction in which a less reactive non-metal is displaced by a more reactive non-metal. 9. Why does the blue colour of copper sulphate change when a piece of iron is dropped into it? Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 17 - 10. In the reactions given below, identify the substances that act as oxidizing and reducing agents: (i) 4Na (s) + O2 (g) → 2Na2O (s) (ii) ZnO (s) + C(s) → Zn(s) + CO (g) 11. Write the balanced chemical equation for the following reactions and identify the type of reaction in each case: (i) Potassium chloride (aq) + Barium iodide (aq) → Potassium iodide (aq) + barium chloride (s) (ii) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g) (iii) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g) (iv) Magnesium (s) + Hydrochloride acid (aq) → Magnesium chloride (aq) + Hydrogen(g) 12. Name the type of reaction involved in the reactions represented by the following equations: (i) CaO + H2O → Ca(OH)2 (ii) Zn + CuSO4 → ZnSO4 + Cu (iii) Al2(SO4)3 + 6NH4OH → 2Al(OH)3 + 3(NH4)2SO4 (iv) CaCO3 → CaO + CO2 (v) H2 + Cl2 → 2HCl 13. Why is magnesium ribbon cleaned before burning it in air? 14. State the characteristics of a chemical reaction. 15. What is a chemical equation? 16. Write the balanced chemical equations for the following chemical reactions: (i) Hydrogen + Chlorine → Hydrogen Chloride (ii) Barium Chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + water → Sodium Chloride + hydrogen 17. Write a balanced chemical equation with state symbols for the following reactions: (i) Solutions of barium chloride and sodium sulphate in water react to give a precipitate of barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloride acid solution (in water) to produce sodium chloride solution and water. 18. How can you explain that respiration is an exothermic reaction? 19. What do you mean by a precipitation reaction? Explain by giving example. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 18 - 20. What are anti-oxidants? Name two substances which are usually used as anti-oxidants. 21. State any two ways to prevent the rancidity of food containing oils and fats. 22. What observations do you expect to get when granulated zinc taken in a test tube is treated with dilute sulphuric acid? 23. Give an example of a chemical reaction which take place with fall in temperature. 24. State on characteristic of chemical reaction taking place when (i) dilute sulphuric acid is made to react with marble chips. (ii) lemon juice is added to a solution of potassium permanganate. (iii) dilute hydrochloride acid is added to a solution of lead nitrate in the cold. (iv) water is added to quick lime. 25. Which of the following reactions are exothermic and which are endothermic? (i) Burning of natural gas (ii) Photosynthesis (iii) Electrolysis of water (iv) Respiration 26. What would you observe when lead nitrate is heated in a test tube? 27. Why is respiration considered an exothermic reaction? 28. Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating. 29. When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are (i) elements (ii)compounds (iii) reactants (iv) products (v) metals (vi) non-metals 30. (a) What is a balanced chemical equation? Why should chemical equations be balanced? (b) Aluminium burns in chlorine to form aluminium chloride. Write a balanced chemical equation for this reaction. LONG ANSWER TYPE QUESTIONS 1. Balance the chemical equations for the following reactions: (i) Cu + H2SO4 → CuSO4 + SO2 + H2O (ii) NaOH + H2SO4 → Na2SO4 + H2O 2. Differentiate between balanced and an unbalanced chemical equation. 3. Write the following chemical equation with state symbols: (i) CaCO3 → CaO + CO2 (ii) 2Na + 2H2O → 2NaOH + H2 (iii) AgNO3 + NaCl → AgCl + NaNO3 Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 19 -  (iv) 6CO2 + 6H2O → C6H12O6 + 6O2 4. What do you mean by exothermic and endothermic reactions? Give examples. 5. What is the difference between displacement and double displacement reactions? Write equations for these reactions. 6. Explain, how do oxidation and reduction processes occur simultaneously. 7. What is corrosion? Write the chemical reaction that takes place during the corrosion of iron? 8. What are the various ways to make a chemical equation more informative? 9. Explain the following terms: (i) corrosion (ii) Rancidity 10. When metal X is treated with a dilute acid Y, then a gas Z is evolved which burns readily by making a little explosion. (a) Name any two metals which can behave like metal X. (b) Name any two acids which can behave like acid Y. (c) Name the gas Z. (d) Is the gas Z lighter than or heavier than air? (e) Is the reaction between metal X and acid Y exothermic or endothermic? (f) By taking a specific example of metal X and dilute acid Y, write a balanced chemical equation for the reaction which takes place. Also indicate physical state of all the reactants and products. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 20 -  ASSIGNMENT QUESTIONS SET – 2 CHAPTER – 1 CHEMICAL REACTIONS AND EQUATIONS 1. What is a balanced chemical equation? Why should chemical equations be balanced? 2. Balance the following chemical equations. a) NaOH + H2SO4 → Na2SO4 + H2O b) Hg (NO3)2 + KI → Hg I2 + KNO3 c) H2 + O2 → H2O d) KClO3 → KCl + O2 e) C3H8 + O2 → CO2 + H2O 3. Write the balanced chemical equations for the following reactions. a) Zinc + Silver nitrate → Zinc nitrate + Silver. b) Aluminum + copper chloride → Aluminum chloride + Copper. c) Hydrogen + Chlorine. → Hydrogen chloride. d) Ammonium nitrate → Nitrogen + Carbon dioxide + water. 4. Write the balanced chemical equation for the following and indentify the type of reaction in each case. a) Calcium hydroxide (aq) + Nitric acid (aq) → Water (l) + Calcium nitrate (aq) b) Magnesium (s) + Iodine (g) → Magnesium Iodide. (s) c) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g) d) Zinc(s) + Calcium chloride (aq) → Zinc Chloride (aq) + Ca(s) 5. Fe2O3 + 2Al → Al2O3 + 2 Fe. The above reaction is an example of: a) Combination reaction b) Decomposition reaction c) Displacement reaction d) Double decomposition reaction 6. What happens when dil.hydrochloric acid is added to iron filings? Chose the correct answer. a) Hydrogen gas and iron chloride are produced. b) Chlorine gas and iron hydroxide are produced. c) No reaction takes place. d) Iron salt and water are produced. 7. Write an equation for decomposition reaction where energy is supplied in the form of heat/ light/ electricity. 8. What do you mean by precipitation reaction? 9. Why is respiration considered as an exothermic reaction? Explain. 10. What is the difference between displacement and double displacement reactions? Write equations for these reactions? 11. What is the use of keeping food in air tight containers? Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 21 - 12. What do you mean by corrosion? How can you prevent it? 13. MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 In the above equation, name the compound which is oxidized and which is reduced? 14. Match the following: 1) 2AgNO3 + Na2CrO4 → Ag2CrO4+ 2NaNO3 ( ) a) combination reactions 2) 2 NH3 → N2+ 3H2 ( ) b) decomposition reactions 3) C2H4 + H2O → C2H6O ( ) c) displacement reactions 4) Fe2O3 + 3CO → 2 F2+ 3CO2 ( ) d) double displacement Reactions 15. Give two examples for oxidation-reduction reaction. 16. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write the reaction involved. 17. Explain rancidity. 18. Name the reactions taking place in the presence of sunlight? 19. 2 PbO(s) + C (s) → 2Pb(s) + CO2 (g) Which of the following statements are correct for the above? a) Lead is reduced. b) Carbon dioxide is oxidized. c) Carbon is oxidized. d) Lead oxide is reduced. i) (a)and (b) ii) (a) and (c) iii) (a), (b), and (c) d) all. 20. Balance the following chemical equations including the physical states. a) C6H12O6 → C2H5OH + CO2 b) Fe + O2 → Fe2O3 c) NH3 + Cl2 → N2H4+NH4cl d) Na + H2O → NaOH +H2 21. Balance the chemical equation by including the physical states of the substances for the following reactions. a) Barium chloride and sodium sulphate aqueous solutions react to give insoluble Barium sulphate and aqueous solution of sodium chloride. b) Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water. c) Zinc pieces react with dilute hydrochloric acid to liberate hydrogen gas and forms zinc chloride 22. Which of the following is not a physical change? (a) Boiling of water to give water vapour (b) Melting of ice to give water (c) Dissolution of salt in water (d) Combustion of Liquefied Petroleum Gas (LPG) 23. The following reaction is an example of a 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) (i) displacement reaction (ii) combination reaction (iii) redox reaction Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 22 -  (iv) neutralisation reaction (a) (i) and (iv) (b) (ii) and (iii) (c) (i) and (iii) (d) (iii) and (iv) 24. Which of the following statements about the given reaction are correct? 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) (i) Iron metal is getting oxidised (ii) Water is getting reduced (iii) Water is acting as reducing agent (iv) Water is acting as oxidising agent (a) (i), (ii) and (iii) (b) (iii) and (iv) (c) (i), (ii) and (iv) (d) (ii) and (iv) 25. Which of the following are exothermic processes? (i) Reaction of water with quick lime (ii) Dilution of an acid (iii) Evaporation of water (iv) Sublimation of camphor (crystals) (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iv) (d) (iii) and (iv) 26. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct? (i) In beakers A and B, exothermic process has occurred. (ii) In beakers A and B, endothermic process has occurred. (iii) In beaker C exothermic process has occurred. (iv) In beaker C endothermic process has occurred. (a) (i) only (b) (ii) only (c) (i) and (iv) (d) (ii) and (iii) 27. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation? (a) KMnO4 is an oxidising agent, it oxidises FeSO4 (b) FeSO4 acts as an oxidising agent and oxidises KMnO4 (c) The colour disappears due to dilution; no reaction is involved (d) KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 23 - 28. Which among the following is(are) double displacement reaction(s)? (i) Pb + CuCl2 → PbCl2 + Cu (ii) Na2SO4 + BaCl2 → BaSO4 + 2NaCl (iii) C + O2 → CO2 (iv) CH4 + 2O2 → CO2 + 2H2O (a) (i) and (iv) (b) (ii) only (c) (i) and (ii) (d) (iii) and (iv) 29. Which among the following statement(s) is(are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to (i) the formation of silver by decomposition of silver chloride (ii) sublimation of silver chloride (iii) decomposition of chlorine gas from silver chloride (iv) oxidation of silver chloride (a) (i) only (b) (i) and (iii) (c) (ii) and (iii) (d) (iv) only 30. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed? (i) It is an endothermic reaction (ii) It is an exothermic reaction (iii) The pH of the resulting solution will be more than seven (iv) The pH of the resulting solution will be less than seven (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iv) (d) (iii) and (iv) 31. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved? (i) Displacement reaction (ii) Precipitation reaction (iii) Combination reaction (iv) Double displacement reaction (a) (i) only (b) (ii) only (c) (iv) only (d) (ii) and (iv) 32. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is (a) 1:1 Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 24 -  (b) 2:1 (c) 4:1 (d) 1:2 33. Which of the following is(are) an endothermic process(es)? (i) Dilution of sulphuric acid (ii) Sublimation of dry ice (iii) Condensation of water vapours (iv) Evaporation of water (a) (i) and (iii) (b) (ii) only (c) (iii) only (d) (ii) and (iv) 34. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate? (a) Lead sulphate (insoluble) (b) Lead acetate (c) Ammonium nitrate (d) Potassium sulphate 35. Which of the following gases can be used for storage of fresh sample of an oil for a long time? (a) Carbon dioxide or oxygen (b) Nitrogen or oxygen (c) Carbon dioxide or helium (d) Helium or nitrogen 36. The following reaction is used for the preparation of oxygen gas in the laboratory Which of the following statement(s) is(are) correct about the reaction? (a) It is a decomposition reaction and endothermic in nature (b) It is a combination reaction (c) It is a decomposition reaction and accompanied by release of heat (d) It is a photochemical decomposition reaction and exothermic in nature 37. Which one of the following processes involve chemical reactions? (a) Storing of oxygen gas under pressure in a gas cylinder (b) Liquefaction of air (c) Keeping petrol in a china dish in the open (d) Heating copper wire in presence of air at high temperature 38. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature? (a) 2H2(l) + O2(l) → 2H2O(g) (b) 2H2(g) + O2(l) → 2H2O(l) (c) 2H2(g) + O2(g) → 2H2O(l) (d) 2H2(g) + O2(g) → 2H2O(g) Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 25 - 39. Which of the following are combination reactions? (a) (i) and (iii) (b) (iii) and (iv) (c) (ii) and (iv) (d) (ii) and (iii) 40. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case. (a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas. (b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water. (c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4. (d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light. 41. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case. (a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide. (b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride. (c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine. (d) Ethanol is burnt in air to form carbon dioxide, water and releases heat. 42. Complete the missing components/variables given as x and y in the following reactions 43. Which among the following changes are exothermic or endothermic in nature? (a) Decomposition of ferrous sulphate (b) Dilution of sulphuric acid (c) Dissolution of sodium hydroxide in water (d) Dissolution of ammonium chloride in water 44. Write the balanced chemical equations for the following reactions (a) Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate. (b) Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 26 -  (c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2 I2), liberates iodine gas and also forms potassium sulphate. 45. Identify the reducing agent in the following reactions 46. Identify the oxidising agent (oxidant) in the following reactions 47. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction? 48. Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction. 49. Why do fire flies glow at night? 50. Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change? 51. Which among the following are physical or chemical changes? (a) Evaporation of petrol (b) Burning of Liquefied Petroleum Gas (LPG) (c) Heating of an iron rod to red hot. (d) Curdling of milk (e) Sublimation of solid ammonium chloride 52. During the reaction of some metals with dilute hydrochloric acid, following observations were made. (a) Silver metal does not show any change (b) The temperature of the reaction mixture rises when aluminium (Al) is added. (c) The reaction of sodium metal is found to be highly explosive (d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid. Explain these observations giving suitable reasons. 53. A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 27 - 54. Write a balanced chemical equation for each of the following reactions and also classify them. (a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution. (b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas. (c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas. (d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water. 55. Why do we store silver chloride in dark coloured bottles? 56. Balance the following chemical equations and identify the type of chemical reaction. 57. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y. (a) Write the chemical formulae of X and Y. (b) Write a balanced chemical equation, when X is dissolved in water. 58. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why? 59. A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. (a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved. (b) Name the black substance formed and give its chemical formula. 60. On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed (a) Write a balanced chemical equation of the reaction. (b) Identity the brown gas X evolved. (c) Identity the type of reaction. (d) What could be the pH range of aqueous solution of the gas X? 61. Give the characteristic tests for the following gases (a) CO2 (b) SO2 (c) O2 (d) H2 62. What happens when a piece of (a) zinc metal is added to copper sulphate solution? (b) aluminium metal is added to dilute hydrochloric acid? (c) silver metal is added to copper sulphate solution? Also, write the balanced chemical equation if the reaction occurs 63. What happens when zinc granules are treated with dilute solution of H2SO4, HCl, HNO3, NaCl and NaOH, also write the chemical equations if reaction occurs. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 28 - 64. On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained. (a) Write a balanced chemical equation of the reaction involved (b) What other name can be given to this precipitation reaction? (c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why? 65. You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO3, ZnCl2 and H2O. In which of the above containers these solutions can be kept? Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 29 -  CHAPTER – 2 ACIDS, BASES AND SALTS ACIDS Acid is a substance which furnishes H+ ions or H3O+ ions when dissolved in water. Acids have one or more replaceable hydrogen atoms. The word acid is derived from the Latin name ‘acidus’ which means sour taste. Substances with ‘sour taste’ are acids. Lemon juice, vinegar and grape juice have sour taste, so they are acidic. They change blue litmus to red. They are colourless with phenolphthalein and pink with methyl orange. There are many substances which contain acid and hence taste sour, such as curd, tamarind, lemon, etc. CLASSIFICATION OF ACIDS 1. Based on their sources : Acids are classified into two types namely organic acids and inorganic acids. Organic acids:- Acids present in plants and animals (living beings) are organic acids eg. HCOOH, CH3COOH (Weak acids). Inorganic acids:- Acids from rocks and minerals are inorganic acids or mineral acids eg. HCl, HNO3, H2SO4 (Strong acids). 2. Based on their basicity Monobasic acid: - It is an acid which gives one hydrogen ion per molecule of the acid in solution eg. HCl, HNO3. Dibasic acid:- It is an acid which gives two hydrogen ions per molecule of the acid in solution e.g., H2SO4, H2CO3. Tribasic acid:- It is an acid which gives three hydrogen ions per molecule of the acid in solution. e.g.,H3PO4, 3. Based on ionisation Acids are classified into two types based on ionisation. Strong acids:- These are acids which ionise completely in water eg.HCl Weak acids:-These are acids which ionise partially in water eg. CH3COOH 4. Based on concentration:- Depending on the percentage or amount of acid dissolved in water acids are classified into concentrated acid and dilute acid. Concentrated acid:- It is an acid having a relatively high percentage of acid in its aqueous solution. Dilute acid:- It is an acid having a relatively low percentage of acid in aqueous solution. INTEXT QUESTIONS PAGE NO. 18 Question 1: You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube? Answer : If the colour of red litmus paper gets changed to blue, then it is a base and if there is no colour change, then it is either acidic or neutral. Thus, basic solution can be easily identified. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 30 - Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put on the red litmus paper. Same is repeated with solution B and C. If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated. Out of the remaining two, any one can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked. If the colour of red litmus turns blue, then the second solution is neutral and if there is no change in colour, then the second solution is acidic. This is because acidic and basic solutions neutralize each other. Hence, we can distinguish between the three types of solutions. CHEMICAL PROPERTIES OF ACIDS REACTION OF ACIDS WITH METAL: Acids give hydrogen gas along with respective salt when they react with a metal. Metal + Acid → Salt + Hydrogen Example: Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal. Zn + 2HCl → ZnCl2 + H2 Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal. 2Na + 2HCl → 2NaCl + H2 Hydrogen gas and iron chloride are formed when hydrochloric acid reacts with iron. Fe + 2HCl → FeCl2 + H2 Hydrogen gas and zinc sulphate are formed when zinc metal reacts with sulphuric acid Zn + H2SO4 → ZnSO4 + H2 REACTION OF ACIDS WITH METAL CARBONATE: Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates. Metal carbonate + Acid → Salt + Carbon dioxide + Water Examples: Sulphuric acid gives calcium sulphate, carbon dioxide gas, calcium sulphate and water when it reacts with calcium carbonate. CaCO3 + H2SO4 → CaSO4 + CO2 + H2O Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium carbonate. Na2CO3 + H2SO4 → Na2SO4 + CO2 + H2O Hydrochloric acid gives carbon dioxide gas, calcium chloride and water when it reacts with calcium carbonate. CaCO3 + 2HCl → CaCl2 + CO2 + H2O Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium carbonate. Na2CO3 + 2HCl → 2NaCl + CO2 + H2O Hydrochloric acid gives carbon dioxide, magnesium chloride and water when it reacts with magnesium carbonate. MgCO3 + 2HCl → MgCl2 + CO2 + H2O Nitric acid gives sodium nitrate, water and carbon dioxide gas when it reacts with sodium carbonate. 2HNO3 + Na2CO3 → NaNO3 + 2H2O + CO2 Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 31 - REACTION OF ACID WITH HYDROGEN CARBONATES (BICARBONATES): Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate. Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water Examples: Hydrochloric acid gives carbon dioxide, sodium chloride and water when it reacts with sodium bicarbonate. NaHCO3 + HCl → NaCl + CO2 + H2O Sulphuric acid gives sodium sulphate, carbon dioxide gas and water when it reacts with sodium bicarbonate. 2NaHCO3 + H2SO4 → Na2SO4 + 2CO2 + 2H2O Sodium bicarbonate is also known as sodium hydrogen carbonate, baking soda, baking powder, bread soda and bicarbonate of soda. The gas evolved because of reaction of acid with metal carbonate or metal hydrogen carbonate turns lime water milky. This shows that the gas is carbon dioxide gas. This happens because of formation of white precipitate of calcium carbonate. Ca(OH)2 + CO2 → CaCO3 + H2O CaCO3 + CO2 + H2O → Ca(HCO3 )2 But when excess of carbon dioxide is passed through lime water, it makes milky colour of lime water disappear. This happens because of formation of calcium hydrogen carbonate. As calcium hydrogen carbonate is soluble in water, thus the milky colour of solution mixture disappears. REACTION OF ACID WITH MARBLE AND EGG SHELL: Since, marble and egg shell are made of calcium carbonate, hence when acid is poured over marble or egg shell, bubbles of carbon dioxide are formed. USES OF ACIDS Sulphuric acid (King of chemicals) is used in car battery and in the preparation of many other compounds. Nitric acid is used in the production of ammonium nitrate which is used as fertilizer in agriculture. Hydrochloric acid is used as cleansing agent in toilet. Tartaric acid is a constituent of baking powder. Salt of benzoic acid (sodium benzoate) is used in food preservation. Carbonic acid is used in aerated drinks. BASES Base is a substance which releases hydroxide ions when dissolved in water. It is a substance which is bitter in taste and soapy to touch (e.g. Washing soda, caustic soda and caustic potash). They change red litmus to blue. They are pink with phenolphthalein and yellow with methyl orange. CLASSIFICATION OF BASES 1. Based on ionisation Strong bases:- These are bases which ionise completely in aqueous solution eg.NaOH, KOH. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 32 -  Weak bases:- These are bases which ionise partially in aqueous solution eg. NH4OH, Ca(OH)2. 2. Based on their acidity Monoacidic base:- It is a base which ionises in water to give one hydroxide ion per molecule eg.NaOH, KOH. Diacidic base:- It is a base which ionises in water to give two hydroxide ions per molecule eg. Ca(OH)2, Mg(OH)2. Triacidic base:- It is a base which ionises in water to give three hydroxide ions per molecule eg. Al(OH)3, Fe(OH)3. 3. Based on the concentration: Depending on the percentage or amount of base dissolved in water, bases are classified as concentrated alkali and dilute alkali. Concentrated alkali:- It is an alkali having a relatively high percentage of alkali in its aqueous solution. Dilute alkali:- It is an alkali having a relatively low percentage of alkali in its aqueous solution. REACTION OF BASE WITH METALS: When alkali (base) reacts with metal, it produces salt and hydrogen gas. Alkali + Metal → Salt + Hydrogen Example: Sodium aluminate and hydrogen gas are formed when sodium hydroxide reacts with aluminium metal. 2NaOH + 2Al + 2H2O → 2NaAlO2 + 2H2 Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal. 2NaOH + Zn → Na2ZnO2 + H2 REACTION OF BASE WITH OXIDES OF NON-METALS: Non-metal oxides are acidic in nature. For example; carbon dioxide is a non-metal oxide. When carbon dioxide is dissolved in water it produces carbonic acid. Therefore, when a base reacts with non-metal oxide both neutralize each other resulting respective salt and water are produced. Base + Non-metal oxide → Salt + Water Example: Calcium hydroxide gives calcium carbonate and water when it reacts with carbon dioxide. Ca(OH)2 + CO2 → CaCO3 + H2O Sodium hydroxide gives sodium carbonate and water when it reacts with carbon dioxide. 2NaOH + CO2 → Na2CO3 + H2O USES OF BASES Sodium hydroxide is used in the manufacture of soap. Calcium hydroxide is used in white washing the buildings. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 33 - Magnesium hydroxide is used as a medicine for stomach troubles. Ammonium hydroxide is used to remove grease stains from clothes. NEUTRALISATION REACTION: An acid neutralizes a base when they react with each other and respective salt and water are formed. Acid + Base → Salt + Water Since in the reaction between acid and base both neutralize each other, hence it is also known as neutralization reaction. Example: Sodium sulphate and water are formed when sulphuric acid reacts with sodium hydroxide (a base). H2SO4 + 2NaOH → Na2SO4 + 2H2O In similar way, when nitric acid reacts with sodium hydroxide, sodium nitrate and water are formed. HNO3 + NaOH → NaNO3 + H2O Sodium chloride and water are formed when hydrochloric acid reacts with sodium hydroxide (a strong base). HCl + NaOH → NaCl + H2O In similar way, calcium chloride is formed along with water when hydrochloric acid reacts with calcium hydroxide (a base). 2HCl + Ca(OH)2 → CaCl2 + 2H2O REACTION OF ACID WITH METAL OXIDES: Metal oxides are basic in nature. Thus, when an acid reacts with a metal oxide both neutralize each other. In this reaction, respective salt and water are formed. Acid + Metal Oxide Salt + Water Example: Calcium is a metal, thus calcium oxide is a metallic oxide which is basic in nature. When an acid; such as hydrochloric acid; reacts with calcium oxide, neutralization reaction takes place and calcium chloride; along with water; is formed. 2HCl + CaO → CaCl2 + H2O Similarly, when sulphuric acid reacts with zinc oxide, zinc sulphate and water are formed. H2SO4 + ZnO → ZnCl2 + H2O When hydrochloric acid reacts with aluminium oxide, aluminium chloride and water are formed. Al2O3 + 6HCl → 2AlCl3 + 3H2O INTEXT QUESTIONS PAGE NO. 22 Question 1: Why should curd and sour substances not be kept in brass and copper vessels? Answer : Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food. Question 2: Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas? Answer : Hydrogen gas is usually liberated when an acid reacts with a metal. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 34 - Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas. We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles. Question 3: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. Answer : COMMON IN ACID AND BASE Acids give hydrogen gas when they react with metal. This shows that all acids contain hydrogen. For example: Hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), etc. When an acid is dissolved in water, it dissociates hydrogen. The dissociation of hydrogen ion in aqueous solution is the common property in all acids. Because of dissociation of hydrogen ion in aqueous solution, an acid shows acidic behavior. Example: Hydrochloric acid (HCl) gives hydrogen ion (H+) and chloride ion (Cl−) when it is dissolved in water. HCl (aq) → H+ + Cl− Sulphuric acid (H2SO4) gives hydrogen ion (H+) and sulphate ion (SO4− −) in water. H2SO4 (aq) → H+ + SO4− − Nitric acid (HNO3) gives hydrogen ion (H+) and nitrate ion (NO3−) in water. HNO3 (aq) → H+ + NO3− Acetic acid (CH3COOH) gives acetate ion (CH3COO−) and hydrogen ion (H+). Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 35 -  CH3COOH (aq) → CH3COO− H+ Hydrogen ion which is produced by acid (when acid is combined with water molecule), exists in the form of hydronium ion (H3O−) in aqueous solution. That’s why hydrogen ion is always written with suffix (aq), such as H+ (aq). HCl + H2O → H3O− + Cl− H2SO4 + H2O → H3O− + SO4− − Thus, because of dissociation of hydrogen ions; acid shows its acidic behavior. Acids conduct electricity in their aqueous solution because of dissociation of hydrogen ion. Hydrogen ion in aqueous solution conducts electricity. A dry acid, such as dry hydrochloric acid does not change the colour of blue litmus paper to red because a dry acid does not dissociate hydrogen ion. This is the cause that a moist litmus paper is used to check the acidic or basic character of a gas. Acidic behavior of carbon dioxide gas: Carbon dioxide gas produces carbonic acid when dissolved in water. This carbonic acid dissociates hydrogen ion and carbonate ion in the aqueous solution. CO2 + H2O → H2CO3 → H+ + CO3− − Are all compounds which contain hydrogen, necessarily acids? No, all compounds which contain hydrogen are not acid. For example; glucose (C6H12O6), methyl alcohol (CH3OH), etc. are not acid in spite of the fact that they contain hydrogen. This is because these compounds do not dissociate hydrogen ion in their aqueous solution. Common in all Base: A base dissociates hydroxide ion in water, which is responsible for the basic behavior of a compound. Example: When sodium hydroxide is dissolved in water, it dissociates hydroxide ion and sodium ion. NaOH (aq) → Na+ + OH− Similarly, when potassium hydroxide is dissolved in water, it dissociates hydroxide ion and potassium ion. KOH (aq) → K+ + OH− Thus, base shows its basic character because of dissociation of hydroxide ion. NEUTRALISATION REACTION: When an acid reacts with a base, the hydrogen ion of acid combines with the hydroxide ion of base and forms water. As these ions combine together and form water; instead of remaining free, thus both neutralize each other. OH− + H+ → H2O Example: When sodium hydroxide (a base) reacts with hydrochloric acid, sodium hydroxide breaks into sodium ion and hydroxide ion and hydrochloric acid breaks into hydrogen ion and chloride ion. Hydrogen ion and hydroxide ion combine together and form water, while sodium ion and chloride ion combine together and form sodium chloride. NaOH + HCl → OH− + Na+ + H+ + Cl− → NaCl + H2O DILUTION OF ACID AND BASE: The concentration of hydrogen ion in an acid and hydroxide ion in a base; per unit volume; shows the concentration of acid or base. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 36 - By mixing of acid to water, the concentration of hydrogen ion per unit volume decreases. Similarly, by addition of base to water the concentration of hydroxide ion per unit volume decreases. This process of addition of acid or base to water is called dilution and the acid or base is called diluted. The dilution of acid or base is exothermic. Thus, acid or base is always added to water and water is never added to acid or base. If water is added to a concentrated acid or base a lot of heat is generated, which may cause splashing out of acid or base and may cause severe damage as concentrated acid and base are highly corrosive. INTEXT QUESTIONS PAGE NO. 25 Question 1: Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? Answer : The dissociation of HCl or HNO3 to form hydrogen ions always occurs in the presence of water. Hydrogen ions (H+) combine with H2O to form hydronium ions (H3O+). The reaction is as follows: Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character. Question 2: Why does an aqueous solution of an acid conduct electricity? Answer : Acids dissociate in aqueous solutions to form ions. These ions are responsible for conduction of electricity. Question 3: Why does dry HCl gas not change the colour of the dry litmus paper? Answer : Colour of the litmus paper is changed by the hydrogen ions. Dry HCl gas does not contain H+ ions. It is only in the aqueous solution that an acid dissociates to give ions. Since in this case, neither HCl is in the aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change. Question 4: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? Answer : Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns. Question 5: How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted? Answer : When an acid is diluted, the concentration of hydronium ions (H3O+) per unit volume decreases. This means that the strength of the acid decreases. Question 6: How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide? Answer : The concentration of hydroxide ions (OH−) would increase when excess base is dissolved in a solution of sodium hydroxide. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 37 - STRENGTH OF ACID AND BASE Acids in which complete dissociation of hydrogen ion takes place are called strong acid. Similarly, bases in which complete dissociation of hydroxide ion takes place are called strong base. In mineral acids, such as hydrochloric acid, sulphuric acid, nitric acid, etc. hydrogen ion dissociates completely and hence they are considered as strong acid. Since, in organic acids hydrogen ions do not dissociate completely, so they are weak acid. Alkalis are water soluble base, thus in alkali; complete dissociation of hydroxide ions takes place and they are considered as strong base. The complete dissociation of hydrogen ions or hydroxide ions is shown by a single arrow. The incomplete dissociation of hydrogen ions or hydroxide ions is denoted by double arrow. Example of complete dissociation: NaOH (aq) → Na+ + OH− HCl → H+ + Cl− Example of incomplete dissociation: Mg(OH)2 → Mg+ + + OH− − CH3COOH → CH3COO− + H+ Although acetic acid being an organic acid is a weak acid, but concentrated acetic acid is corrosive and can damage the skin if poured over it. pH – MEASUREMENT OF STRENGTH OF ACID AND BASE pH stands for the power of hydrogen ion concentration in a solution. pH values decide whether a solution is acidic or basic or neutral. pH scale was introduced by S.P.L. Sorenson. It is mathematically expressed as pH = -log10[H+] For neutral solution [H+] = 10–7M; pH = 7 For acidic solution [H+] > 10–7M; pH < 7 For basic solution [H+] < 10–7M; pH > 7 When OH– ions are taken into account the pH expression is replaced by pOH pOH = -log10[OH–] The strength of acid or base depends upon the hydrogen ion concentration. If the concentration of hydrogen ion is greater than hydroxide ion, the solution is called acidic. If the concentration of hydrogen ion is smaller than the hydroxide ion, the solution is called basic. If the concentration of hydrogen ion is equal to the concentration of hydroxide ion, the solution is called neutral solution. pH is a scale which quantifies the concentration of hydrogen ion in a solution. The range of pH scale is between 0 to 14. The pH value decreases with increase in hydrogen ion concentration. If the value of pH is 0, this shows maximum hydrogen ion concentration. pH value equal to 14 shows lowest hydrogen ion concentration. pH value equal to 7 shows the hydrogen ion concentration is equal to hydroxide ion concentration. Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 38 - A neutral solution, such as distilled water has value of hydrogen ion concentration equal to 7 on pH scale. The acidic solution has value of hydrogen ion concentration less than 7 on pH scale. The basic solution has value of hydrogen ion concentration greater than 7 on pH scale. In pH scale ‘p’ stands for ‘potenz’. Potenz is a German word which means ‘power’ or ‘potential’. Here; ‘H’ stands for hydrogen ion. Thus, pH means the potential of hydrogen or power of hydrogen. IMPORTANCE OF pH IN EVERYDAY LIFE 1. pH in human body Using pH factor the healthiness of our body is predicted. At pH level 6.9, the body becomes prone to viral infections like colds, cough and flu. Cancer cells thrive inside the body at a pH of 5.5. The pH of a normal, healthy human skin is 4.5 to 6. Proper skin pH is essential for a healthy complexion. pH of stomach fluid is approximately 2.0. This fluid is essential for the digestion of food. Human blood pH range is 7.35 to 7.45. Any increase or decrease in this value, leads to diseases. The ideal pH for blood is 7.4. pH of normal saliva ranges between 6.5 to 7.5. White enamel coating in our teeth is calcium phosphate, hardest substance in our body. It does not dissolve in water. If pH of mouth falls below 5.5, the enamel gets corroded. Toothpastes are generally basic, and is used for cleaning the teeth, can neutralize the excess acid and prevent tooth decay. 2. pH in soil In agriculture, the pH of soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugar cane requires neutral soil. 3. pH in rain water pH of rain water is approximately 7 showing high level of its purity and neutrality. If rain water is polluted by SO2 and NO2, acid rain occurs, bringing the pH value less than 7. INDICATOR: Substances which show the acidic or basic behavior of other substance by change in colour are known as indicator. Type of Indicator: There are many types of indicators. Some common types of indicators are  Natural  Olfactory Indicator  Synthetic Indicator  Universal Indicator Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 39 - NATURAL INDICATOR Indicators obtained from natural sources are called natural indicators. Litmus, turmeric, red cabbage, China rose, etc. are some common natural indicators used widely to show the acidic or basic character of substances. LITMUS Litmus is obtained from lichens. The solution of litmus is purple in colour. Litmus paper comes in two colour – blue and red.  An acid turns blue litmus paper red.  A base turns red litmus paper blue. TURMERIC Turmeric is another natural indicator. Turmeric is yellow in colour. Turmeric solution or paper turns reddish brown with base. Turmeric does not change colour with acid. RED CABBAGE The juice of red cabbage is originally purple in colour. Juice of red cabbage turns reddish with acid and turns greenish with base. OLFACTORY INDICATORS Substances which change their smell when mixed with acid or base are known as olfactory indicators. For example onion, vanilla, clove, etc. ONION Paste or juice of onion loses its smell when added with base. It does not change its smell with acid. VANILLA The smell of vanilla vanishes with base, but it’s smell does not vanishes with an acid. Olfactory indicators are used to ensure the participation of visually impaired students in laboratory. SYNTHETIC INDICATOR Indicators that are synthesized in laboratory are known as synthetic indicators. For example; phenolphthalein, methyl orange, etc. Phenolphthalein is a colourless liquid. It remains colourless with acid but turns into pink with a base. Methyl orange is originally orange in colour. It turns into red with acid and turns into yellow with base. Indicator Original colour Acid Base Red litmus Red No change Blue Blue litmus Blue Red No change Turmeric Yellow No change Reddish brown Red cabbage juice Purple Reddish Greenish yellow Phenolphthalein Colourless Colourless Pink Methyl orange Orange Red Yellow Onion n/a No change Smell vanishes Vanilla n/a No change Smell vanishes Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 40 - UNIVERSAL INDICATOR: Using a litmus paper, phelophthalein, methyl orange, etc. only the acidic or basic character of a solution can be determined, but use of these indicators does not give the idea about the strength of acid or base. So, to get the strength as well as acidic and basic nature of a given solution universal indicator is used. Universal indicator shows different colour over the range of pH value from 1 to 14 for a given solution. Universal indicator is available both in the form of strips and solution. Universal indicator is the combination of many indicators, such as water, propanol, phelophthalein, sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt. The colour matching chart is supplied with universal indicator which shows the different colours for different values of pH. INTEXT QUESTIONS PAGE NO. 28 Question 1: You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic? Answer : A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic. Question 2: What effect does the concentration of H+(aq) ions have on the nature of the solution? Answer : Concentration of H+(aq) can have a varied effect on the nature of the solution. With an increase in H+ ion concentration, the solution becomes more acidic, while a decrease of H+ ion causes an increase in the basicity of the solution. Question 3: Do basic solutions also have H+(aq) ions? If yes, then why are these basic? Answer :Yes, basic solution also has H+(aq) ions. However, their concentration is less as compared to the concentration of OH− ions that makes the solution basic. Question 4: Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)? Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 41 - Answer : If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk. SALT Salts are the ionic compounds which are produced after the neutralization reaction between acid and base. Salts are electrically neutral. There are number of salts but sodium chloride is the most common among them. Sodium chloride is also known as table salt or common salt. Sodium chloride is used to enhance the taste of food. CHARACTERISTICS OF SALT:  Most of the salts are crystalline solid  Salts may be transparent or opaque  Most of the salts are soluble in water  Solution of salts conducts electricity. Salts conduct electricity in their molten state also  The salt may be salty, sour, sweet, bitter and umami (savoury)  Neutral salts are odourless  Salts can be colourless or coloured Classification of salts 1. Normal salts A normal salt is obtained by complete neutralization of an acid by a base NaOH + HCl → NaCl + H2O 2. Acid salts Acid salts are derived by the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained, as follows. NaOH + H2SO4 → NaHSO4 + H2O 3. Basic salts Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base by an acid radical. A basic salt may further reacts with an acid to give a normal salt. Pb(OH)2 + HCl → Pb(OH)Cl + H2O Diacidic base Basic salt 4. Double salts Double salts are formed by the combination of saturated solution of two simple salts in equimolar ratio followed by crystallization. e.g. potash alum FAMILY OF SALT: Salts having common acidic or basic radicals are said to belong to same family. Example Sodium chloride (NaCl) and Calcium chloride (CaCl2) belong to chloride family. Calcium chloride (CaCl2) and calcium sulphate (CaSO4) belong to calcium family. Zinc chloride (ZnCl2) and Zinc sulphate (ZnSO4) belong to zinc family. ACIDIC, BASIC AND NEUTRAL SALTS NEUTRAL SALT Salts produced because of reaction between strong acid and strong base are neutral in nature. The pH of value of such salts is equal to 7, i.e. neutral. Example; Sodium chloride, sodium sulphate, potassium chloride, etc. Sodium chloride (NaCl) is formed after the reaction between hydrochloric acid (a strong acid) and sodium hydroxide (a strong base). Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 42 - NaOH + HCl → NaCl + H2O SODIUM SULPHATE (Na2SO4) It is formed after the reaction between sodium hydroxide (a strong base) and sulphuric acid (a strong acid). 2NaOH + H2SO4 → Na2SO4 + 2H2O Potassium chloride (KCl): It is formed after the reaction between potassium hydroxide (a strong base) and hydrochloric acid (a strong acid). KOH + HCl → KCl + H2O ACIDIC SALT Salts which are formed after the reaction between a strong acid and weak base are called acidic salt. The pH value of acidic salt is lower than 7. Example: ammonium sulphate, ammonium chloride, etc. Ammonium chloride is formed after reaction between hydrochloric acid (a strong acid) and ammonium hydroxide (a weak base). NH4OH + HCl → NH4Cl + H2O Ammonium sulphate is formed after reaction between ammonium hydroxide (weak base) and sulphuric acid (a strong acid). 2NH4OH + H2SO4 → (NH4 )2SO4 + 2H2O BASIC SALT Salts which are formed after the reaction between weak acid and strong base are called basic salt. For example; sodium carbonate, sodium acetate, etc. Sodium carbonate is formed after the reaction between sodium hydroxide (a strong base) and carbonic acid (a weak base). H2CO3 + 2NaOH → Na2CO3 + 2H2O Sodium acetate is formed after the reaction between a strong base, sodium hydroxide and a weak acid, acetic acid. CH3COOH + NaOH → CH3COONa + H2O CAUSE OF FORMATION OF ACIDIC, BASIC AND NEUTRAL SALT: When a strong acid reacts with a weak base, the base is unable to fully neutralize the acid. Due to this an acidic salt is formed in this case. When a strong base reacts with a weak acid, the acid is unable to fully neutralize the base. Due to this a basic salt is formed in this case. When equally strong acid and base react they fully neutralize each other. Due to this a neutral salt is formed in this case. pH Value Of Salt:  Neutral salt: The pH value of a neutral salt is almost equal to 7.  Acidic salt: The pH value of an acidic salt is less than 7.  Basic salt: The pH value of a basic salt is more than 7. COMMON SALT (SODIUM CHLORIDE) Sodium chloride (NaCl) is also known as common or table salt. It is formed after the reaction between sodium hydroxide and hydrochloric acid. It is a neutral salt. The pH value of sodium Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 43 - chloride is about 7. Sodium chloride is used to enhance the taste of food. Sodium chloride is used in manufacturing of many chemicals. IMPORTANT CHEMICALS FROM SODIUM CHLORIDE: SODIUM HYDROXIDE (NaOH) Sodium hydroxide is a strong base. It is also known as caustic