NCERT Solutions for Class 10 Science Chapter 1 Question Answers.pdf

NCERT Solutions for Class 10 Science Chapter 1 – Chemical Reactions And Equations Intext Exercise 1 1. Why should a magnesium ribbon be cleaned before burning in air? Ans: Magnesium is a reactive metal. It will react with oxygen and for...

NCERT Solutions for Class 10 Science Chapter 1 – Chemical Reactions And Equations Intext Exercise 1 1. Why should a magnesium ribbon be cleaned before burning in air? Ans: Magnesium is a reactive metal. It will react with oxygen and form a white layer of magnesium oxide (MgO) on its surface. Magnesium oxide is a stable compound and will prevent the further reaction of the metal. So, a magnesium ribbon is cleaned before burning in air to remove the layer of magnesium oxide from its surface. 2. Write the balanced equation for the following chemical reactions. i) Hydrogen + Chlorine → Hydrogen chloride Ans: A balanced equation consists of the same number of moles on the reactants and the products side. The balanced equation for the given reaction is: H 2( g ) + Cl2( g ) → 2HCl( g ) ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride Ans: A balanced equation consists of the same number of moles on the reactants and the products side. The balanced equation for the given reaction is: 3BaCl2( s ) + Al2 ( SO4 )3( s ) → 3BaSO4( s ) + 2 AlCl3( s ) iii) Sodium + Water → Sodium hydroxide + Hydrogen Ans: A balanced equation consists of the same number of moles on the reactants and the products side. The balanced equations for the given reaction is 2 Na( s ) + 2 H 2O(l ) → 2 NaOH ( aq ) + H 2( g ). 3. Write a balanced chemical equation with state symbols for the following reactions. Class X Science www.vedantu.com 1 i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. Ans: A balanced chemical equation has the same number of moles of reactants and products.The balanced chemical equation is: BaCl2( aq ) + Na2 SO4( aq ) → BaSO4( s ) + 2 NaCl( aq ) ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water. Ans: A balanced chemical equation has the same number of moles of reactants and products. The balanced chemical equation is: NaOH ( aq ) + HCl( aq ) → NaCl( aq ) + H 2O(l ). Intext Exercise 2 1. A solution of a substance 'X ' is used for white washing. i) Name the substance 'X' and write its formula. Ans: Substance ‘X’ is calcium oxide also known as quicklime that is used in white washing. Its chemical formula is CaO. ii) Write the reaction of the substance 'X' named in (i) above with water. Ans: Calcium oxide reacts with water in a combination reaction to from calcium hydroxide also called slaked lime, the reaction is: CaO( s ) + H 2O(l ) → Ca(OH )2( aq ). 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. Ans: Water consists of hydrogen and oxygen atoms. It is a combination of two hydrogen and one oxygen atom. In electrolysis, hydrogen moves towards the cathode and oxygen towards the anode. So, the ratio of hydrogen and oxygen is 2:1. And hydrogen is double the amount of oxygen. 2H 2O → 2H 2 + O2 Class X Science www.vedantu.com 2 Intext Exercise 3 1. Why does the color of copper sulphate solution change when an iron nail is dipped in it? Ans: When an iron nail is dipped in a solution of copper sulphate, then the more reactive metal displaces the less reactive metal. As a result the blue solution of copper sulphate gets faded and forms a green compound known as ferrous sulphate. Fe( s ) + CuSO4( aq ) → FeSO4( aq ) + Cu( s ) Iron Copper sulphate Ferrous sulphate Copper (Blue) (Green ) 2. Give an example of a double displacement reaction other than the one given in Activity 1.10. Ans: A double displacement reaction consists of two ions replacing each other’s position from the reactants to form new compounds in the products. A double displacement reaction occurs when Potassium iodide reacts with lead nitrate to form lead iodide (yellow precipitate) and potassium nitrate. 2KI + Pb( NO3 )2 → PbI 2  +2 KNO3 Class X Science www.vedantu.com 3 3. Identify the substances that are oxidised and the substances that are reduced in the following reactions i) 4Na (s) +O2(g) → 2Na 2O(s) Ans: Any species is said to be oxidised when it loses electrons and increases the oxidation state, while any species is said to be reduced when it gains electrons and decreases the oxidation state. Sodium (Na) is oxidised and oxygen gets reduced. 4Na + O2 → 2Na 2O ii) CuO(s) +H2(g) → Cu(s)+H2O(l) Ans: Any species is said to be oxidised when it loses electrons and increases the oxidation state, while any species is said to be reduced when it gains electrons and decreases the oxidation state. Copper oxide (CuO) is reduced to copper (Cu) as it loses oxygen and hydrogen ( H 2 ) is oxidized to water ( H 2O)  CuO + H 2 ⎯⎯ → Cu + H 2O NCERT exercises 1. Which of the statements about the reaction below are incorrect? 2PbO(s) +C(s) → 2Pb(s) +CO2(g) a. Lead is getting reduced. b. Carbon dioxide is getting oxidised. c. Carbon is getting oxidised. d. Lead oxide is getting reduced. Options i) (a) and (b) Class X Science www.vedantu.com 4 ii) (a) and (c) iii) (a),(b) and (c) iv) all Ans: Incorrect option is (i) (a) and (b) Explanation:(a) Oxygen is being removed (b) The Oxygen removed from lead is transferred to the elemental Carbon. 2. Fe2O3 +2Al → Al2O3 +2Fe The above reaction is an example of a _______________ Options: a) Combination reaction. b) Double displacement reaction. c) Decomposition reaction. d) Displacement reaction. Ans: (d) The given reaction is an example of a single displacement reaction. Explanation: The oxygen from ferrous oxide is transferred to aluminum metal, forming aluminum oxide. In this reaction, aluminum, being more reactive than iron, displaces iron from its oxide. This process is known as a displacement reaction, where a more reactive element replaces a less reactive one. 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, Class X Science www.vedantu.com 5 d. Iron salt and water are produced. Ans: (a) Hydrogen gas and iron chloride are produced. The reaction is as follows: Fe( s ) + 2 HCl( aq ) → FeCl2( aq ) + H 2  4. What is a balanced chemical equation? Why should chemical equations be balanced? Ans: A balanced chemical equation consists of the equal number of moles of the elements in the reactants and that in the products. Chemical equations should be balanced, as according to the law of conservation of mass, mass can neither be created nor can be destroyed. Therefore, in a chemical reaction, the total mass of reactant should be equal to the total mass of products. Hence, a balanced chemical equation has total mass of reactants equal to total mass of products. 5. Translate the following statements into chemical equations and then balance them. a) Hydrogen gas combines with nitrogen to form ammonia. Ans: 3H 2( g ) + N2( g ) → 2 NH 3( g ) b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide. Ans: 2H 2 S( g ) + 3O2( g ) → 2H 2O(l ) + 2SO2( g ) c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. Ans: 3BaCl2( aq ) + Al2 (SO4 )3( aq ) → 2 AlCl3( aq ) + 3BaSO4( s ) d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas Ans: 2K( s ) + 2H 2O(l ) → 2KOH ( aq ) + H 2( g ) 6. Balance the following chemical equations a) HNO3 + Ca(OH)2 → Ca ( NO3 )2 + H 2O Ans: 2 HNO3 + Ca(OH )2 → Ca ( NO3 )2 + 2H 2O Class X Science www.vedantu.com 6 b) NaOH + H2SO4 → Na 2SO4 + H2O Ans: 2 NaOH + H 2 SO4 → Na2 SO4 + 2H 2O c) NaCl + AgNO3 → AgCl + NaNO3 Ans: NaCl + AgNO3 → AgCl + NaNO3 d) BaCl2 +H2SO4 → BaSO4 +HCl Ans: BaCl2 + H 2 SO4 → BaSO4 + 2HCl. 7. Write the balanced chemical equations for the following reactions. a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water Ans: Ca(OH )2 + CO2 → CaCO3 + H 2O b) Zinc + Silver nitrate → Zinc nitrate +Silver Ans: Zn + 2 AgNO3 → Zn ( NO3 )2 + 2 Ag c) Aluminium + Copper chloride → Aluminium chloride + Copper Ans: 2 Al + 3CuCl2 → 2 AlCl3 + 3Cu d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride Ans: BaCl2 + K2 SO4 → BaSO4 + 2KCl 8. Write the balanced chemical equation for the following and identify the type of reaction in each case. Class X Science www.vedantu.com 7 a) Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s) Ans: 2KBr( aq ) + BaI 2( aq ) → 2KI ( aq ) + BaBr2( aq ) ; Double displacement reaction b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g) Ans: ZnCO3( s ) → ZnO( s ) + CO2( g ) ; Decomposition reaction c) Hydrogen (g)+ Chlorine (g) → Hydrogen chloride (g) Ans: H 2( g ) + Cl2( g ) → 2HCl( g ) ; Combination reaction d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g) Ans: Mg( s ) + 2HCl( aq ) → MgCl2( aq ) + H 2( g ) ; Single displacement reaction 9. What does one mean by exothermic and endothermic reactions? Give examples. Ans: Exothermic Reaction: The reactions in which heat is evolved along with the formation of new products are called exothermic reactions. In these reactions the energy of the reactants is more than that of the products, so energy is released to complete the reaction. Energy of reactants > Energy of products Example: Complete combustion of methane gas produces carbon dioxide and water along with heat and light. CH 4 ( g ) + 2O2 ( g ) → CO2 + 2H 2O + heat + light Another example of exothermic reactions is respiration and decomposition of vegetable matter. Class X Science www.vedantu.com 8 Endothermic Reaction: The reactions in which energy is absorbed by the reactants to carry on the reaction are called endothermic reactions. In this type of reaction, the energy of the reactants is less than that of the products, so energy is needed and absorbed. Energy of reactants