1. As statement (a) and (b) are incorrect, answer (i) is correct.
2. This is an example of displacement reaction because Fe in FeO3 has been displaced by Al. Hence correct answer is (d).
3. Answer (a) is correct.
4. The reaction in which the number of atoms of each element is equal on the reactant side and product side is called balanced equation.
Chemical reaction should be balanced because only a balanced equation tells us the relative quantities of different reactants and products involved in the reaction.
5. (a) H2 +N2 → NH3
3H2 + N2 → 2NH3
(b) H2S + O2 → H2O + SO2
2H2S + 3O2 → 2H20 + 2SO2
(c) BaCl2 + Al2(SO4)3 → AlCl3 +BaSO4
3BaCl2 + Al2(SO2)3 → 2AlCl3 +3BaSO4
(d) K + H2O → KOH + H2
2K + 2H20 → 2KOH + H2
6. Balanced chemical equation are
(a) 2HNO3 + Ca(OH)2 → Ca(OH)2 Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(C) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
7. Balanced chemical equation for reactions are
a. Ca(OH)2 + CO2 → CaCO3 + H2O
b. Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
c. 2Al + 3Cl2 → 2AlCl3 + 3Cu
d. BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Balanced equations are
a. 2KBr (aq) + BaI2 ( aq) → 2KI (aq) + Br2 (displacement reaction)
b. ZnO3 (s) → ZnO (s) + CO2 (g) (decomposition reaction)
c. H2 (g) + Cl2 (g) → 2HCl (combination reaction)
d. Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) (displacement reaction)
9. A reaction in which energy is released in the form of heat or light is called exothermic reaction. Example of exothermic reaction are :
a. CH4 + 2O2 → CO2 + 2H2O + heat
b. 2Al + FeO3 → Al2O3 + Fe + heat
A reaction in which energy is absorbed from the surrounding and cooling is
produced is called endothermic reaction. Example of exothermic reaction are :
a. CaCO3 → CaO + CO2
b. N2 + O2 → 2NO
10. During respiration, we inhale oxygen from the atmosphere which reacts with
glucose in your body cells to produce carbon dioxide and water.
C6H12O6 (aq) + 6O2 → 6CO2 (g) + 6H2O (1) + heat
Heat is liberated in this process; hence respiration is considered an exothermic reaction.
11. NH4Cl (s) → HCl (g) + NH3 (g)
In a decomposition reaction, a single substance breaks down into two or more substance while in a combination reaction, two or more substances react to produce one substance. Therefore decomposition reactions are called opposite of combination reactions.
Example of decomposition reaction: Example of combination reaction:
CaO (s) + CO2 (g) → CaCO3 (s)
12. Decomposition by heat:
CaCO3(S) + heat → CaO (s) + CO2 (g)
Decomposition by electricity:
2H2O + light → 2H2 (g) + O2 (g)
Decomposition by light:
2AgBr (s) + light → 2Ag (s) + Br2
13. In displacement reaction, more reactive element displaces the less reactive element from its compound. For example
Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
But in double displacement reaction, exchange of ions takes place. For example
HCl (aq) + AgNO3 (aq) → AgCl (s) + HNO3 (aq)
14. The reaction involved is:
AgNO3 (aq) + Cu (s) → AgCl (s) + Cu(NO3)2 (aq) + 2Ag (s)
15. A chemical reaction in which an insoluble substance (precipitate) is formed is called precipitation reaction. For example
AgNO3 + NaCl → AgCl + NaNO3
16. Oxidation- addition of oxygen or removal of hydrogen in a chemical reaction is called oxidation reaction. For example
2Cu + O2 → 2CuO
4Al + 3O2 → 2Al2O3
Reduction- addition of hydrogen or removal of oxygen in a chemical reaction is called oxidation reaction. For example
CuO +H2 → Cu +H2O
H2S + Cl2 → 2HCl +S
17. The brown coloured element ‘X ‘ is copper. On heating in air it forms copper oxide,
which is black in colour.
2CuS + O2 → 2CuO
18. We apply paint on iron articles to prevent rusting. Iron articles do not come in
contact of atmospheric oxygen and moisture and thus the rusting is prevented.
19. Oil and fat containing items get rancid due to oxidation with atmospheric oxygen. To
prevent rancidity food items are flushed with nitrogen. Nitrogen do not reacts with oil and fat containing items.
20. Corrosion– action of air, water, acid or other substance on metal surface to form
oxides and carbonates is called corrosion. Corrosion of iron is called rusting. Green coating on copper and black coating on silver is examples of corrosion. Rancidity-change in smell of food item containing fat and oil when kept open for longer time due to oxidation is called rancidity. To prevent rancidity food items are flushed with nitrogen or kept in airtight containers.
21. Magnesium ribbon is cleaned before burning to remove the protective layer of basic
magnesium carbonate from the surface of magnesium ribbon.
22. The chemical equations are as follows-
i. H2 + Cl2 → 2HC
ii. 3BaCl2 + Al2 (SO4)3 → 3BaSO4 + 2AlCl3
iii. 2Na + 2H2O → 2NaOH + H2
Balance chemical reaction with state symbols are as follows-
i. BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)
ii. NaOH (aq) + HCl (aq) → NaCl (aq) + H2O
23. (i). The substance whose solution is water is used for white washing is calcium Its formula is CaO.
(ii). CaO (s) + H2O → Ca(OH)2 (s)
24. 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 element as compared to only 1 part of oxygen element.
25. When iron nail is dipped in copper sulphate solution, than iron sulphate solution and copper solution and copper metal are formed:
CuSO4 (aq) + Fe (s) → FeSO4 (aq) + Cu (s)
In this reaction, iron displaces copper from copper sulphate solution. The deep blue colour of copper sulphate fades due to the formation of light green solution of iron sulphate.
26. An example of double displacement reaction is
Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)
27. (i) 4Na + O2 → 2Na2O
In this reaction, Na is oxidized because it combines with O2 to form Na2O. O2 is reduced because it is converted into Na2O.
(ii) CuO + H2 → Cu + H2O
In this reaction, CuO is reduced because it loses oxygen. H2 is oxidized because it combines with oxygen of CuO to form water.