Chemical Reaction
Chapter 1
Chemical Reactions and Equations
Q.1. Why should magnesium ribbon be cleaned before burning in air ?
Ans: Magnesium ribbon is a very reactive metal. When stored it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide being a stable compound prevents further reaction of magnesium with oxygen. The magnesium is cleaned before burning in air to remove this layer so that the metal can be exposed to air properly.
Q.2. Write the balanced equation for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrogen chloride
Ans. H2 (g) + Cl2 (g) → 2HCl (g) (ii) Sodium + Water --> Sodium hydroxide + Hydrogen
Ans: 2Na (s) + 2H2O (liq) → 2NaOH (aq) + H2 (g).
Q.3. Write a balanced chemical equation with state symbols for the following chemical reactions:
(i) Solution of barium chloride and sodium sulphate in water to give insoluble barium sulphate and the solution of sodium chloride.
Ans:- (i) BaCl2 (aq) + Na2SO4 (aq) →BaSO4 (s) + 2NaCl (aq)
(ii) Sodium hydroxide solution (in water) react with hydrochloric acid solution (in water) to produce sodium chloride and water.
Ans. (ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (liq)
Q.4. A reaction of a substance X is used for white washing.
(i) Name the substance X and write its formula. Ans.The substance X is lime which is used for white washing. Its formula is CaO.
(ii) Write the reaction of the substance X named in (i) above with water.
Ans: CaO + H2O → Ca(OH)2 + Heat
Q.5. 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 contains two parts of hydrogen and one part oxygen. Therefore, during
Chemical Reactions and Equations
Q.1. Why should magnesium ribbon be cleaned before burning in air ?
Ans: Magnesium ribbon is a very reactive metal. When stored it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide being a stable compound prevents further reaction of magnesium with oxygen. The magnesium is cleaned before burning in air to remove this layer so that the metal can be exposed to air properly.
Q.2. Write the balanced equation for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrogen chloride
Ans. H2 (g) + Cl2 (g) → 2HCl (g) (ii) Sodium + Water --> Sodium hydroxide + Hydrogen
Ans: 2Na (s) + 2H2O (liq) → 2NaOH (aq) + H2 (g).
Q.3. Write a balanced chemical equation with state symbols for the following chemical reactions:
(i) Solution of barium chloride and sodium sulphate in water to give insoluble barium sulphate and the solution of sodium chloride.
Ans:- (i) BaCl2 (aq) + Na2SO4 (aq) →BaSO4 (s) + 2NaCl (aq)
(ii) Sodium hydroxide solution (in water) react with hydrochloric acid solution (in water) to produce sodium chloride and water.
Ans. (ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (liq)
Q.4. A reaction of a substance X is used for white washing.
(i) Name the substance X and write its formula. Ans.The substance X is lime which is used for white washing. Its formula is CaO.
(ii) Write the reaction of the substance X named in (i) above with water.
Ans: CaO + H2O → Ca(OH)2 + Heat
Q.5. 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 contains two parts of hydrogen and one part oxygen. Therefore, during