NCERT Solution : chemical reactions and equations
NCERT Book page – 6
Q1. Why should a magnesium ribbon be cleaned before burning in air?
Ans :- A magnesium ribbon is cleaned to remove the protective layer of basic magnesium carbonate from its surface so that it may readily combine with the oxygen of air(on heating)
Q2. Write the balanced equations for the following chemical reactions :-
(i). Hydrogen + chlorine \longrightarrow hydrogen chloride
(ii) Barium chloride + Aluminium sulphate \longrightarrow Barium sulphate + aluminium chloride
(iii) Sodium + water \longrightarrow sodium hydroxide + hydrogen
Ans :- (i) H_2 + Cl_2 \longrightarrow 2HCl
(ii) 3BaCl_2 + Al_2(SO_4)_3 \longrightarrow 3BaSO_4 + 2AlCl_3
(iii) 2Na + 2H_2 O \longrightarrow 2NaOH + H_2
Q3:- write balanced chemical equations with state symbols for the following reactions :-
(i) solution of barium chloride and sodium sulphate in water react to give insoluble barium chloride and the solution of sodium chloride .
(ii) sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution in water.
Ans :-
(i) BaCl_2 (aq.) + Na_2 SO_4 (aq) \longrightarrow BaSO_4 (s) + 2NaCl (aq)
(ii) NaOH (aq.) + HCl (aq) \longrightarrow NaCl (aq) + H_2 O (l)
NCERT Book page – 10
Q1 :- A solution of 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.
Ans :- (i) The substance whose solution in water we use for white washing is calcium oxide(lime , choona) . so , the substance X is calcium oxide . its formula is CaO.
(ii) CaO (s) + H_2 O (l) \longrightarrow Ca(OH)_2 (s)
Q2 :- why is double the amount of a gas collected in one of the test tubes in the electrolysis of water activity ? Name this gas.
Ans :- The gas which is collected in double the amount in the electrolysis of water experiment is hydrogen . This is because water contains 2 parts of hydrogen elements and 1 part of oxygen elements.
NCERT Book page – 13
Q1 :- 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 copper sulphate solution , then the blue color of copper sulphate solution changes because iron displaces copper from copper sulphate solution to form a light green solution of iron sulphate.
Q2:- Give an example of a double displacement reaction?
Ans :- when silver nitrate solution is added to sodium chloride solution , then a double displacement reaction takes place in which a white precipitate of silver chloride is formed along with sodium nitrate solution.
Q3:- identify the substances that are oxidized and the substances that are reduced in the following reactions :-
(i) 4Na(s) + O_2 (g) \longrightarrow 2Na_2 O(s)</span> <span style="color: #ff0000;">
(ii) CuO(s) + H_2 (g) \longrightarrow</span> <span style="color: #ff0000;">Cu(s) + H_2 O(l)
Ans :-
- (i) substance oxidized :- Na ; substance reduced :- O_2
- (ii)substance oxidized :- H_2 ; substance reduced :- CuO
NCERT Book page – 14 , 15 and 16
Q1 :- which of the statements about the reaction below are incorrect ?
2PbO (s) + C(s) \longrightarrow 2Pb(s) + CO_2 (g)
- (a) lead is getting reduced
- (b) carbon dioxide is getting oxidized
- (c) carbon is getting oxidized
- (d) lead oxide is getting reduced
- (a) and (b)
- (a) and (c)
- (a) , (b) , and (c)
- all
Ans :- 1 (a) and (b)
Q2:- Fe_2 O_3 + 2 Al \longrightarrow Al_2 O_3 + 2Fe
- (a) combination reaction
- (b) double displacement reaction
- (c) decomposition reaction
- (d) displacement reaction
Ans :- (d) displacement reaction.
Q3:- what happen when dilute hydrochloric acid is added to iron filling ? 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.
Ans :- (a) hydrogen gas and iron chloride are produced.