Answer: - ‘Al’ is reducing agent.
4. Why should a magnesium ribbon be cleaned before burning in air ? Answer: To remove the layer of MgO.
5. What does one mean by exothermic and endothermic reactions ? Give examples. Answer: Exothermic reactions : heat is evolved
Example : (i) C (s) + O2 (g) → CO2 (g) + Heat
(ii) N2 (g) + 3H2 (g) → 2NH3 (g) + Heat Endothermic reactions : heat is absorbed
Examples :(i) C (s) + 2S (s) → CS2 (l) – Heat
(ii) N2 (g) + O2 (g) → 2NO(g) – Heat
6. Name the type of chemical reaction represented by the following equation:
i) CaO + H2O → Ca(OH )2
ii).3BaCl2 +Al2 (SO4 )3 → 3BaSO4 2AlCl3
iii) 2FeSO4 + heat → Fe2O3 + SO2 + SO3
Answer:- (i) Combination reaction
(ii) Double displacement reaction (Precipitation reaction)
(iii) Thermal Decomposition reaction.
7. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer:- It is because water contains hydrogen and oxygen in the ratio of 2 : 1.
8. Ferrous sulphate crystals are heated in a dry boiling tube.
(i) List any two observations.
(ii) Name the type of chemical reaction taking place.
(iii) ‘Write the chemical equation for the reaction. Answer:-
(i) Two observations are
(a) change in colour
(b) Smell of burning sulphur
(ii) Decomposition reaction
2FeSO4 + heat Fe2O3 + SO2 + SO3
9. What is observed when a solution of
potassium iodide solution is added to a solution of lead nitrate? Name the type
of reaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer:- Yellow
precipitate is formed. It is precipitation reaction.
Pb (NO3)2 (aq) + 2KI ® Pbl2 + 2KNO3
10. Which products will be obtained when lead nitrate
is heated simply?
Write balanced chemical equation for the reaction.
Answer: -
2Pb( NO3)2(s) ® 2PbO(s) + 4NO2(g) + O2(g)
11.
when an iron nail is dipped
in copper sulphate solution?
Answer.
It is because displacement reaction takes place.
12. Why are decomposition reactions
called the opposite of combination reactions? Write equations for these reactions.
Answer. In decomposition reaction, a compound is broken down into simpler
compounds or elements, e.g.
CuCO3(s) ® CuO(s) + CO2 (g)
Combination reaction is a reaction in which two or more elements or compounds combine to form a new compound, e.g.
N2 (g) + 3H2 ® 2NH3 (g)
Thus, decomposition and combination reactions are opposite to each other.
13. The following diagram displays a
chemical reaction. Observe carefully and answer the following questions
(a)
Identify the type
of chemical reaction that will take place and define it.
(b)
How
will the color of the salt change? Write the chemical equation of the reaction
that takes place.
(c)
Mention
one commercial use of this salt.
Answer. (a)
Photochemical decomposition reaction.
(b)
The colour of salt will change from white to grey.
(c) in photography
14.
What
is rancidity? Mention any two ways by which rancidity can be prevented. Answer.
Spoilage of food containing
oil.
Prevention
from rancidity:-
(i) Antioxidants
(ii) airtight
container in refrigerator.
15.
A solution of substance ‘X’ is used
for white washing. What is the substance ‘X’? State the chemical reaction of
‘X’ with water.
Answer. ‘X’ is calcium
oxide (CaO).
CaO(s) + H2O(l ) ® Ca (OH )aq) + heat
16. Define combination reaction. Give one example
of a combination reaction which is also exothermic.
Answer. A reaction in which two elements or compounds combine to form a
single compound is called combination reaction.
CaO(s) +
H2O(l ) ® Ca (OH )aq) + heat
17.
(a) Why is
respiration considered as an exothermic reaction?
(b) Identify the
substance that is oxidized and reduced in the following reaction.
CaO(s) + Zn(s) ® Cu(s) + ZnO(s)
Answer. (a) It is because
heat is evolved during respiration.
(b) Zn is
getting oxidised, CuO is getting reduced.
18.
Translate the
following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and
Sulphur dioxide.
(c)
Barium chloride
reacts with aluminum
sulphate to give aluminum chloride
and a precipitate of barium sulphate.
(d)
Potassium
metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer: (a) 3H2 (g) + N2
(g) → 2NH3 (g)
(b) H2S (g) + 3O2 (g) → SO2 (g) + 2H2O(l)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) →
2AlCl3
(aq) + 3BaSO4 ↓(s)
(d) 2K (s) + 2H2O (l) →
2KOH (aq) + H2 (g)
19. Write the balanced chemical
equation for the following and identify the type of reaction in each case :
(a) Potassium bromide (aq) + Barium iodide (aq) →
Potassium iodide (aq) + Barium
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide
(g) bromide(s)
(c) Hydrogen (g) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride
(aq) + Hydrogen (g)
Answer:(a) 2KBr(aq) +
Bal2 (aq) ® 2Kl (aq) +
BaBr2 (s)
Type : Double
displacement reaction
(b) ZnCO3 (s) ® ZnO (s) + CO2
(g
)
Type :
Decomposition reaction
(c) H2 (g ) +
Cl2 (g ) ® 2HCl (g )
Type :
Combination reaction
(d) Mg(s) +
2HCl(aq) ® MgCl2 (aq) + H2
(g
)
Type :
Displacement reaction
20. Complete the
missing components/variables given as x and y in the following reactions :
Answer:
