9th Grade Science: Acids, Bases and Salts PDF

# Acids, Bases and Salts ## Chapter Outline - Arrhenious theory of acids and bases - Concentration of an acid or a base - pH of a solution - Reactivity of acids and bases - Salts ## Important Points ### 1. Ionic Compounds There are three types of ionic compounds: acids, bases and salts. Ionic compounds have two constituents: a cation (positive ion) and anion (negative ion). The force of attraction between one positive charge on a cation and one negative charge on an anion is called the ionic bond. **Example:** Sodium chloride (NaCl) **Can you recall?** On mixing the substances as shown, what are the resulting mixtures formed by mixing the following substances? 1. Water and salt 2. Water and sugar 3. Water and sand 4. Water and sawdust **Answer:** Substances 1 and 2 are homogeneous mixtures, as sugar and salt both dissolve in water. Substances 3 and 4 are heterogeneous mixtures, as sand and sawdust do not dissolve in water. ### 2. Dissociation of Ionic Compounds When a solid ionic compound begins to dissolve in water, the water molecules push themselves in between the ions of the compound and separate them from each other. It means an ionic compound dissociates during the formation of an aqueous solution. **Example:** **NaCl(s)** **Na(aq) + Cl(aq)** **Water** **(dissociation)** ### 3. Acid A substance which on dissolving in water gives rise to H+ ion as the only cation is called an acid. **Example:** **HCl** **HNO3** **Water** **(dissociation)** **Water** **(dissociation)** **H(aq) + Cl(aq)** **H(aq) + NO3(aq)** ### 4. Base A substance which on dissolving in water gives rise to the OH- ion as the only anion is called a base. **Example:** NaOH, Ca(OH)2 **NaOH(s)** **Water** **(dissociation)** **Na(aq) + OH(aq)** **Ca(OH)2(s)** **Water** **(dissociation)** **Ca2+(aq) + 2OH(aq)** ### 5. Classification of Acids and Bases - **Strong acid:** An acid, on dissolving in water, dissociates completely, and the resulting aqueous solution contains H+ ions and the concerned acidic radicals. This is called a strong acid. **Examples:** HCl, HNO3, H2SO4 - **Weak acid:** An acid, on dissolving in water, does not dissociate completely, and the resulting aqueous solution contains H+ ions and the concerned acidic radicals in small proportion along with a large proportion of the undissociated molecules of the acid. This is called a weak acid. **Examples:** H2CO3 (carbonic acid), CH3COOH (acetic acid). - **Strong Base:** A base, on dissolving in water, dissociates completely, and the resulting aqueous solution contains OH- ions and the concerned basic radicals. This is called a strong base. **Examples:** NaOH, KOH - **Weak base:** A base, on dissolving in water, does not dissociate completely, and the resulting aqueous solution contains OH- ions and the concerned basic radicals in small proportion along with a large proportion of the undissociated molecules of the base. This is called a weak base. **Example:** NH4OH - **Alkali:** The bases which are highly soluble in water are called alkali. **Examples:** NaOH, KOH, while NH3 is a weak alkali. ### 6. Basicity of Acids The number of H+ ions obtainable by the dissociation of one molecule of an acid is called its basicity. ### 7. Acidity of Bases The number of OH- ions obtainable by the dissociation of one molecule of a base is called its acidity. ### 8. Concentration of Acid and Base The proportion of a solute in a solution is called the concentration of the solute in the solution. When the concentration of a solute in its solution is high, it is a concentrated solution. When the concentration of a solute in its solution is low, it is a dilute solution. To express the concentration of a solution, several units are used: - **Grams per litre:** The mass of solute in grams dissolved in one litre of the solution is called gram per litre (g/L). - **Molarity (M):** The number of moles of the solute dissolved in one litre of the solution is called the molarity (M) of the solution. ### 9. The pH of Solution pH is a number which indicates the acidic or basic nature of a solution. It helps in measuring hydrogen ion concentration in a solution. ### 10. pH Scale On the pH scale we can measure pH from 0 (very acidic solution) to 14 (very alkaline solution). pH is a number which indicates the strength of the acidic or basic nature of a solution. The scale used for measuring hydrogen ion concentration in a solution is formed as pH scale. The higher the hydronium ion concentration, the lower is the pH value. When pH value is in between 0 to 7, the solution is acidic in nature and when pH value is in between 7 to 14, the solution is alkaline/basic in nature. Neutral solution has a pH equal to 7. Pure water has a pH of 7. It means pure water has (H+) = 1 x 10-7 mol/L. pH 7 indicates a neutral solution. At 25°C, the concentration of H+ ions in 1 M solution of HCl is 1.19 mol/L. While in a 1 M NaOH solution, the concentration of H+ ions is 1 x 10-14 mol/L. ## Questions and Answers **Fill in the blanks:** 1. Ionic compound _______ in aqueous solution. 2. _______ is a weak alkali. 3. The number of H+ ions obtained form one molecule of H3PO4 are _______. 4. The number of OH ions obtained from one molecule of Ca(OH)2 are _______. 5. The proportion of a solute in a solution is called the _______ of the solute. 6. When the concentration of a solute in its solution is low, it is a _______ solution. 7. In the _______ reaction, an acid reacts with a base to form a salt and water. 8. The pH of a basic solution is _______ than 7. 9. The separation of ions form an electrolyte is termed as _______. 10. The positive terminal of an electrolytic cell is called _______. **Answers:** 1. dissociates 2. NH3 3. 3 4. 2 5. concentration 6. dilute 7. neutralization 8. greater 9. dissociation 10. an anode **Fill in the blanks by choosing the correct alternative and rewrite the completed statements:** 1. At what pH value is the solution considered to be acidic? * a) 6 * b) 7 * c) 10 * d) 14 2. What is the colour of a universal indicator in neutral solution? * a) red * b) blue * c) greenish yellow * d) green 3. Which of the following solutions has pH more than 7? * a) Pure water * b) NaOH solution * c) HCl solution * d) Lemon juice 4. Which of the following solutions has pH 7? * a) Pure water * b) HNO3 solution in water * c) Na2CO3 solution in water * d) HCl solution in water 5. Which of the following is a synthetic indicator? * a) Phenolphthalein * b) Beet * c) Litmus * d) Turmeric 6. The mixture of several indicators is known by which of the following indicators? * a) universal indicator * b) olfactory indicator * c) natural indicator * d) synthetic indicator 7. Phenolphthalein is _______. * a) the natural indicator * b) the synthetic indicator * c) an olfactory indicator * d) the universal indicator 8. When phenolphthalein is added to NaOH, the colour of the solution will become _______. * a) colourless * b) red * c) pink * d) yellow 9. When phenolphthalein is added to HCl, the colour of the solution will be _______. * a) red * b) pink * c) green * d) colourless 10. _______ is a natural indicator. * a) Phenolphthalein * b) Methyl orange * c) Litmus * d) Methyl red 11. The litmus paper or the litmus solution is obtained from _______ plants. * a) Moss * b) Rose * c) Hibiscus * d) Lichen 12. Which of the following is not required to find the pH of a given solution? * a) pH paper * b) Litmus paper * c) Standard pH chart * d) Universal indicator 13. _______ colour will be obtained by adding universal indicator in baking soda solution. * a) Blue * b) Greenish blue * c) Dark blue * d) Violet 14. Na2SO4 is ______ salt. * a) a general * b) an acidic * c) a basic * d) a neutral 15. _______. * a) Litmus * b) Lichen * c) Litmus paper **Answers:** 1. At what pH value is the solution considered to be acidic? **a) 6** 2. What is the colour of a universal indicator in neutral solution? **c) greenish yellow** 3. Which of the following solutions has pH more than 7? **b) NaOH solution** 4. Which of the following solutions has pH 7? **a) Pure water** 5. Which of the following is a synthetic indicator? **a) Phenolphthalein** 6. The mixture of several indicators is known by which of the following indicators? **a) universal indicator** 7. Phenolphthalein is **b) the synthetic indicator**. 8. When phenolphthalein is added to NaOH, the colour of the solution will become **c) pink**. 9. When phenolphthalein is added to HCl, the colour of the solution will be **d) colourless**. 10. **c) Litmus** is a natural indicator. 11. The litmus paper or the litmus solution is obtained from **d) Lichen** plants. 12. Which of the following is not required to find the pH of a given solution? **d) Universal indicator** 13. **b) Greenish blue** colour will be obtained by adding universal indicator in baking soda solution. 14. Na2SO4 is **d) a neutral** salt. 15. **c) Litmus paper** **State whether the following statements are True or False. If a statement is false, correct it and rewrite it:** 1. Acids have bitter taste. 2. KCl is a stable ionic compound. 3. pH scale helps in measuring hydrogen ion concentration in a solution. 4. The pH of rain water is 7. 5. Salts of strong acids and strong bases are basic with the pH value greater than 7. 6. Salts of strong acids and weak bases are acidic with the pH value less than 7. 7. KOH is a monobasic acid. 8. The bases which are highly soluble in water are called alkali. 9. Sodium chloride is a crystalline compound. 10. During electrolysis of water, hydrogen gas is formed near the anode. **Answers:** 1. **False**. (Acids have sour taste.) 2. **True**. 3. **True**. 4. **False**. (The pH of rain water is 6.5.) 5. **False**. (Salts of strong acids and strong bases are neutral with the 7 pH value.) 6. **True**. 7. **False**. (KOH is a monoacidic base) 8. **True**. 9. **False**. (Sodium chloride is a ionic compound.) 10. **False**. (During electrolysis of water, hydrogen gas is formed near the cathode.) **Find the odd one out and justify:** 1. Chloride, nitrate, hydride, ammonium. 2. Acetic acid, carbonic acid, hydrochloric acid, nitric acid. 3. Hydrogen chloride, sodium hydroxide, calcium oxide, ammonia. 4. Ammonium chloride, sodium chloride, potassium nitrate, sodium sulphate. 5. Sodium nitrate, sodium carbonate, sodium sulphate, sodium chloride. 6. Calcium oxide, magnesium oxide, zinc oxide, sodium oxide. 7. Crystalline blue vitriol, crystalline common salt, crystalline ferrous sulphate, crystalline sodium carbonate. 8. Sodium chloride, potassium hydroxide, acetic acid, sodium acetate. 9. HCl, CH3COOH, H2SO4, HNO3. 10. NaOH, Ca(OH)2, NH4OH, Ba(OH)2. 11. H2SO4, H2CO3, HCl, HNO3. 12. Citric acid, formic acid, lactic acid, nitric acid. **Answers:** 1. **Ammonium** (Others are anions.) 2. **Acetic acid** (Others are inorganic acids.) 3. **Hydrogen chloride** (Others are bases.) 4. **Ammonium chloride** (Others are neutral salts.) 5. **Sodium carbonate** (Others are neutral salts.) 6. **Zinc oxide** (Others are basic oxides.) 7. **Crystalline common salt** (Others are crystalline substances contain water of crystallization.) 8. **Acetic acid** (Others are electrolytes.) 9. **CH3COOH** (Others are strong acids.) 10. **NaOH** (Others are weak bases.) 11. **H2CO3** (Others are strong acids.) 12. **Nitric acid** (Others are organic acids.) **Consider the relation between Column I and II match the Column III:** | Column I | Column II | Column III | |---|---|---| | Base | a) blue in acidic and neutral medium | i) calcium hydroxide | | Acetic acid | b) blue litmus red in acidic medium | ii) red in alkaline medium | | Red litmus | c) hydroxide ion | iii) single hydrogen ion | | Black coffee | d) monobasic acid | iv) pH = 5 | **Answers:** 1. Base - hydroxide ion - **calcium hydroxide** **Answer the following questions in one sentence each:** 1. Explain the dissociation of an ionic compound? 2. What is meant by an alkali? 3. What is meant by a concentration of the solute in the solution? 4. What is meant by a concentrated solution? 5. What is meant by a dilute solution? 6. How do you measure pH on a pH scale? 7. What would be the pH of a salt of a weak acid and a strong base? 8. What would be the pH of a salt of a strong acid and a strong base/ 9. What is the pH range of human blood at which it works? 10. Name an electrical instrument which can measure pH accurately. **Answers:** 1. When a solid ionic compound begins to dissolve in water, the water molecules push themselves in between the ions of the compound and separate them from each other. It means, an ionic compound dissociates during the formation of an aqueous solution. 2. The bases which are highly soluble in water are called alkali. 3. The proportion of a solute in a solution is called the concentration of the solute in the solution. 4. When the concentration of a solute in its solution is high, it is called a concentrated solution. 5. When the concentration of a solute in its solution is low, it is called a dilute solution. 6. On pH scale we can measure pH from 0 (very acidic solution) to 14 (very alkaline solution). 7. The pH of a salt of a weak acid and strong base is more than 7. 8. The pH of a salt of a strong acid and strong base is about 7. 9. The human blood works within pH range of 7.35 to 7.45. 10. The most accurate method of measuring the pH of a solution is to use an electrical instrument called pH meter. **Fill in the columns in the part A of the following table:** | Name of the compound | Molecular Formula | Basic radical | Acidic radical | Type of the compound | |---|---|---|---|---| | Hydrochloric acid | HCl | H+ | Cl- | Acid | | Nitric acid | HNO3 | H+ | NO3- | Acid | | Hydrogen bromide | HBr | H+ | Br- | Acid | | Sulphuric acid | H2SO4 | H+ | SO42- | Acid | | Boric acid | H3BO3 | H+ | BO33- | Acid | | Sodium hydroxide | NaOH | Na+ | OH- | Base | | Potassium hydroxide | KOH | K+ | OH- | Base | | Calcium hydroxide | Ca(OH)2 | Ca2+ | OH- | Base | | Ammonium hydroxide | NH4OH | NH4+ | OH- | Base | | Sodium chloride | NaCl | Na+ | Cl- | Neutral | | Calcium nitrate | Ca(NO3)2 | Ca2+ | NO3- | Neutral | | Potassium sulphate | K2SO4 | K+ | SO42- | Neutral | | Calcium chloride | CaCl2 | Ca2+ | Cl- | Neutral | | Ammonium sulphate | (NH4)2SO4 | NH4+ | SO42- | Neutral | **Complete the following table:** | Acid | Number of H+ obtained from one molecule | |---|---| | HCl | H+ | | HNO3 | H+ | | H2SO4 | 2H+ | | H2CO3 | 2H+ | | H3BO3 | 3H+ | | H3PO4 | 3H+ | | CH3COOH | H+ | | Base | Number of OH- obtained from one molecule | |---|---| | NaOH | OH- | | KOH | OH- | | Ca(OH)2 | 2OH- | | Ba(OH)2 | 2OH- | | Al(OH)3 | 3OH- | | Fe(OH)3 | 3OH- | | NH4OH | OH- | **Complete the following table of the concentration of various aqueous solutions:** | Solute | Quantity of solute | Volume of solution | Concentration of solution | |---|---|---|---| | Name | Molecular formula | Molecular mass (u) | Gram (g) | Mole | Litre (L) | Gram/litre (g/L) | Molarity (M) | | Sodium chloride | NaCl | 58.5 u | 117 g | 2 mol | 2 L | 58.5 g/L | 1 M | | Hydrogen chloride | HCl | 36.5 u | 3.65 g | 0.1 mol | 1 L | 3.65 g/L | 0.1 M | | Sodium hydroxide | NaOH | 40 u | 60 g | 1.5 mol | 2 L | 30 g/L | 0.75 M | **Complete the reactions in the following table:** | Carbonate salt of metal | Dilute acid | Another salt of metal | Carbon dioxide | |---|---|---|---| | Na2CO3(s) | 2HCl(aq) | 2NaCl(aq) | CO2(g) + H2O | | Na2CO3(s) | H2SO4(aq) | Na2SO4(aq) | CO2(g) + H2O | | CaCO3(s) | 2HNO3(aq) | Ca(NO3)2(aq) | CO2(g) + H2O | | K2CO3(s) | H2SO4(aq) | K2SO4(aq) | CO2(g) + H2O | **Complete the reactions in the following table:** | Carbonate salt of metal | Dilute acid | Another salt of metal | Carbon dioxide | |---|---|---|---| | NaHCO3(s) | HCl(aq) | NaCl(aq) | CO2(g) + H2O | | KHCO3(s) | HNO3(aq) | KNO3(aq) | CO2(g) + H2O | | NaHCO3(s) | CH3COOH(aq) | CH3COONa(aq) | CO2(g) + H2O | **Questions based on reactions:** **1. Complete the following table of neutralization reactions and also write down the names of the acids, bases and salts in it.** | Acid + base | Salt | Water | |---|---|---| | HNO3 + | KNO3 | H2O | | + 2NH4OH | (NH4)2SO4 | | | + KOH | KBr | | **Answers:** 1. HNO3 + KOH → KNO3 + H2O * Nitric acid + Potassium hydroxide → Potassium nitrate + Water 2. H2SO4 + 2NH4OH → (NH4)2SO4 + H2O * Sulphuric acid + Ammonium hydroxide → Ammonium sulphate + Water 3. HBr + KOH → KBr + H2O * Hydrogen bromide + Potassium hydroxide → Potassium bromide + Water **2. Complete the following reactions:** | Metal | Dilute acid | Salt | Water | |---|---|---|---| | Mg(s) | 2HCl(aq) | MgCl2(aq) | H2(g) | | Zn(s) | H2SO4(aq) | ZnSO4(aq) | H2(g) | | Cu(s) | 2HNO3(aq) | Cu(NO3)2(aq) | H2(g) | **3. Complete the following reactions:** | Metal oxide | Dilute acid | Salt | Water | |---|---|---|---| | CaO(s) | 2HCl(aq) | CaCl2 | H2O | | MgO(s) | 2HCl(aq) | MgCl2(aq) | H2O | | ZnO(s) | 2HCl(aq) | ZnCl2(aq) | H2O | | Al2O3(s) | 6HF(l) | 2AlF3(aq) | 3H2O(l) | **4. Complete the following reactions:** | Non-metal oxide | Base | Salt | Water | |---|---|---|---| | CO2(g) | 2NaOH(aq) | Na2CO3(aq) | H2O | | H2CO3 | 2KOH(aq) | K2CO3(aq) | 2H2O | | SO3(g) | 2NaOH(aq) | Na2SO4(aq) | H2O | **Write down the concentration of each of the following solutions in g/L and mol/L:** 1. 7.3 g HCl in 100 ml solution 2. 2 g NaOH in 50 ml solution 3. 3 g CH3COOH in 100 ml solution 4. 4.9 H2SO4 in 200 ml solution **Answers:** | Solute | Quantity of solute | Volume of solution | Concentration of solution | |---|---|---|---| | Name | Molecular formula | Molecular mass (u) | Gram (g) | Mole | Litre (L) | Gram/litre (g/L) | Molarity (M) | | Hydrochloric acid | HCl | 36.5 u | 7.3 g | 0.2 mol | 100 ml (0.1 L) | 73 g/L | 2 mol/L | | Sodium hydroxide | NaOH | 40 u | 2 g | 0.05 mol | 50 ml (0.05 L) | 40 g/L | 1 mol/L | | Acetic acid | CH3COOH | 60 u | 3 g | 0.05 mol | 100 ml (0.1 L) | 30 g/L | 0.5 mol/L | | Sulphuric acid | H2SO4 | 98 u | 4.9 g | 0.05 mol | 200 ml (0.2 L) | 24.5 g/L | 0.25 mol/L | **Read the questions based on the acidic or basic nature of a solution** pH is a number which indicates the acidic or basic nature of a solution. It helps in measuring hydrogen ion concentration in a solution. In a sample of rain water a few drops of universal indicator are added and the pH of rain water is measured. Now three samples of pure water are taken separately. The first sample of pure water is treated with a few drops of universal indicator and the pH of pure water is determined. In the second sample of water, lemon juice is mixed and then treated with a few drops of universal indicator, the pH of lemon juice solution is measured. In the third sample of pure water, small quantity of washing soda is mixed and then treated with a few drops of universal indicator, the pH of this washing soda solution is measured. **Questions:** 1. What is meant by a pH of a solution? 2. What is the pH of rain water? 3. What is the pH of pure water? 4. What is the pH of lemon juice solution? 5. What is the pH of washing soda solution? **Answers:** 1. pH is a number which indicates the acidic or basic nature of a solution. It helps in measuring hydrogen ion concentration in a solution. 2. The rain water is slightly acidic and its pH is 6.5. 3. The pure water is neutral in nature and its pH is 7. 4. The lemon juice solution is acidic in nature and its pH is less than 7. 5. The washing soda solution is alkaline in nature and its pH is greater than 7. **Activity Based Questions:** 1. **Take some water in a test tube and add a little red oxide (the primer used before painting iron articles) to it. Now add a small quantity of dilute HCl to it, shake the test tube and observe.** * Does the red oxide dissolve in water? * What change takes place in the particles of red oxide on adding dilute HCl? **Answers:** * The red oxide does not dissolve in water. * The water insoluble red oxide reacts with HCl to produce a water soluble salt FeCl3. This gives yellowish colour to water. Fe2O3(s) + 6HCl(aq) → 2FeCl3(aq) + 3H2O **2. Prepare 10 ml aqueous solutions from 1 gm each of sodium chloride, ammonium chloride and sodium bicarbonate. Measure pH of each solution by means of pH paper. Are the values the same for all three? Classify the salts based on the pH values.** **Answers:** The pH values are not the same for three salt solutions. * pH of sodium chloride solution = 7 - Neutral * pH of ammonium chloride solution is less than 7 - Acidic * pH of sodium bicarbonate solution is greater than 7 - Basic **3. Ionic compounds and electrical conductivity:** **Activity:** Prepare a solution of 1 g sodium chloride in 50 ml water. Take two electrical wires. Connect one wire to the positive terminal of a battery. While connecting the other wire to the negative terminal of the battery, include one switch and one holder with an electric bulb. Remove the insulating cladding from 3 cm portion of the other free ends of the two wires. Take the salt solution in a 100 ml capacity beaker and immerse the uncovered ends of the two wires in it keeping the wire erect with the help of a support. Switch on the current. Note whether the bulb glows. Repeat the same procedure using solutions of 1 g copper sulphate, 1g glucose, 1 g urea, 5 ml dilute H2SO4 and 5 ml dilute NaOH each in 50 ml water. Record your observations in a table. **(Do not forget to clean the beaker and uncovered part of the wires with water, every time you change the solution.)** **Observations:** **Salts, Acid and Base** | | Electric circuit | Electric current through a bulb | Bulb | |---|---|---|---| | In aqueous solution the compounds NaCl, CuSO4, H2SO4 and NaOH dissociate completely. Cations and anions are formed on a large scale. Anions move in the direction of the anode and cations move in the direction of the cathode. The movement of ions in the solution towards the respective electrodes amounts to the conduction of electricity through the solution. Electrons conduct electricity through electrical wires and ions conduct electricity through a liquid or solution. | Electric circuit is completed | Electric current flows through the bulb | Bulb glows | | In aqueous solution of glucose and urea, ions are not formed. | Electric circuit is not completed | Electric current does not flow through the bub | Bulb does not glow | **4. Electrolysis of water:** **Study the procedure given below and answer the following questions:** **Dissolve 2 g salt in 500 ml pure water. Take 250 ml of this solution in a 500 ml capacity beaker. Connect two electrical wires to the positive and negative terminals of a power supply. Remove the insulating cladding from about 2 cm portions at the other ends of the wires. These are the two electrodes. Fill two test tubes up to the brim with the prepared dilute salt solution. Invert them on the electrodes without allowing any air to enter. Start the electric current under 6 V potential difference form the power supply. Observe what happens in the test tubes after some time.** * Did you see the gas bubbles forming near the electrodes in the test tubes? * Are these gases heavier or lighter than water? * Are the volumes of the gases collected over the solution in the two test tubes the same or different? * Test the solutions in the two test tubes with litmus paper, what do you see? **Answers:** * The gas bubbles formed near the electrodes in the test tubes are seen. * These gases are lighter than water. * The volumes of the gases collected over the solution in the two test tubes are different. * The volume of the H2 gas formed near the cathode is double that of the O2 gas formed near the anode. * **Cathode reaction:** 2H2O(l) + 2e- → H2(g) + 2OH-(aq) * **Anode reaction:** 2H2O(l) → O2(g) + 4H+(aq) + 4e- * When you test the solutions in the two test tubes with litmus paper you will see that the litmus paper turns blue in the tube containing the hydrogen gas and turns red in the tube containing the oxygen gas. **Repeat the activity by using dilute H2SO4 as well as dilute NaOH as the electrolyte. (Students should perform this experiment in the laboratory with the help of teachers.)** **Draw the diagram to represent the above procedure. (Board's specimen activity sheet)** **Name the gases released at the cathode and anode. (Board's specimen activity sheet)** **Write down the changes that will be seen in each instance and explain the reason behind it.** * 50 ml water is added to 50 ml solution of copper sulphate. * Two drops of the indicator phenolphthalein were added to 10 ml solution of sodium hydroxide. * Two or three filings of copper were added to 10 ml dilute nitric acid and stirred. * A litmus paper was dropped into 2 ml dilute HCl. Then 2 ml concentrated NaOH was added to it and stirred. * Magnesium oxide was added to dilute HCl and magnesium oxide was added to dilute NaOH. * Dilute HCl was added to lime stone. * Zinc oxide was added to dilute HCl and zinc oxide was added to dilute NaOH. * Pieces of blue vitriol were heated in a test tube. On cooling water was added to it. * Dilute H2SO4 was taken in an electrolytic cell and electric current was passed through it. * Would water be a good conductor of electricity? **Answers:** 1. When 50 ml water is added to 50 ml solution of copper sulphate, the blue colour of aqueous solution of copper sulphate fades and also the concentration of copper sulphate solution decreases. 2. When two drops of the indicator phenolphthalein were added to 10 ml of NaOH, it develops light pink colour. 3. When two or three filings of copepr were added to 10 ml dilute nitric acid, it forms copper nitrate and hydrogen gas. 4. A piece of litmus paper was added into 2 ml dilute HCl, blue litmus turns red. When in the same solution 2 ml concentrate NaOH was added and stirred, then the red litmus turned blue. 5. When magnesium oxide was added to dil. HCl, it forms magnesium chloride and water. Magnesium oxide being basic in nature it neutralizes acid. There is no reaction between magnesium oxide and dil. NaOH, as both are basic in nature. 6. When dilute HCl was added to lime stone, it forms calcium chloride, water and carbon dioxide gas. 7. When zinc oxide was added to dilute HCl, it forms zinc chloride and water. In this reaction, zinc oxide is a basic oxide. When zinc oxide was added to dilute NaOH, it forms sodium zincate and water. In this reaction, zinc oxide is an acidic oxide. Therefore, zinc oxide is an amphoteric oxide because it shows both acidic and basic properties 8. When pieces of blue vitriol were heated in a test tube, the crystalline structure of blue vitriol broke down to form colurless powder and water evaporates. On cooling when water was added to colourless powder, blue vitriol regains its blue colour. All the above changes are physical changes. 9. When electric current was passed through dilute H2SO4

9th Grade Science: Acids, Bases and Salts PDF

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