1. In one of the industrial process used for manufacture of sodium hydroxide, a gas ‘X’ is formed as by – product. The gas ‘X’ reacts with lime water to give a compound ‘Y’ which is used as a bleaching agent in chemical industry. Identify ‘X’ and ‘Y’ giving the chemical equation of the reaction.
Ans: In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by products. When chlorine gas (X) reacts with lime water, it forms calcium oxy chloride (bleaching powder) Y.
2NaCl (aq) + 2 H2O (L)----> 2NaOH (Aq) + Cl2 (G) + H2 (G)
‘X’ Þ Cl2 gas
Ca(OH)2 + Cl2----> CaOCl2 + H2O
Q. Dry hydrogen chloride gas does not turn blue litmus, whereas hydrochloric acid does. Why?
Ans: In the dry state, hydrogen chloride (HCl) does not release H+ ions. Therefore, it cannot behave as an acid. When dissolved in water, it forms hydrochloric acid. It dissociates to give H+ ions in solution and behaves as an acid.
Acid when react with metals release hydrogen gas but there is one acid which when reacts with metals does not release hydrogen except for two metals. Prove this statement.
Acid + Metal ----> Salt + Hydrogen
e.g. 2HCl + 2Na ---->2NaCl + H2
H2SO4 + 2Na ----> Na2SO4 + H2
HNO3 + Na ---->No hydrogen gas.
Because nitric acid is strong oxidising agent. Nitric acid reacts only with Mg and Mn to give hydrogen gas.
Mg + 2HNO3 ----> Mg(NO3)2 + H2
Mn + 2HNO3---->Mn(NO3)2 + H2
Q. 4 Name the properties responsible for the following uses of baling powder. (i) Baking industry (ii) As an antacid (ii) As soda-acid fire extinguisher.
Q. 5 What is meant by water of crystallisation of a substance? What is its importance?
Q. 6 What effect does an increase in concentration of ‘H’ ions in a solution have on the pH of a solution
Q. 7 Fresh milk has a pH Of 6. When it changes to curd, will its pH value increase or decrease? Why?
Q. 8 How does the flow of acid rain water into a river make the survival of aquatic life in a river difficult?
Q. 9 Arrange in the increasing order of their pH values: NaOH solution, Blood, Lemon juice,
Q. 10 Two solutions A and B have pH values of 5 and 8 respectively. Which solution will be basic in nature?
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