Chemical Reactions Test

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Chemical Reactions Test - 5

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following statements are true regarding a catalyst?

I. It is a substance which increases the rate of the reaction.
II. It is a substance which reduces the activation energy.
III. It is a substance which increases the activation energy.
IV. It is a substance which is consumed in the reaction.

A
I and II

B
II and III

C
III and IV

D
I and IV

Solution

Catalyst is a substance which increases the rate of a reaction. It reduces the activation energy for the reaction by providing a new pathway for the reaction to proceed. In case of heterogeneous catalysis it provides the surface for the gaseous reactants to interact.
A catalyst is never consumed during the reaction and is always regenerated in the end.
Hence, only statements I and II are correct.
Question 2
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Which of the following options is true for all chemical reactions?

A
Heat is evolved.

B
There is a change in volume.

C
Chemical bonds are broken or formed.

D
There is a change in mass.

Solution

Chemical bonds are broken or formed. From the given options, this is true for all chemical reactions.
Question 3
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In the synthesis of NH₃ from N₂ and H₂, Fe and Mo (Molybdenum) are used to alter the speed of the reaction. In this process, Mo acts as

A
a catalyst

B
a negative catalyst

C
a promoter

D
an auto catalyst

Solution

In the synthesis of NH₃ from N₂ and H₂, Fe and Mo are used to alter the speed of the reaction. In this process, Mo acts as a promoter.
A promoter, is a substance added to a solid catalyst to improve its performance in a chemical reaction.
Question 4
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Which of the following best explains the action of a catalyst in enhancing the rate of a chemical reaction?

A
It decreases the energy of activation of the reaction.

B
It prevents the reverse reaction from occurring.

C
It increases the value of equilibrium constant of the reaction.

D
It increases the kinetic energy of the molecules.

Solution

Catalyst decreases the energy of activation of the reaction, which enhances the rate of a chemical reaction.
Both kinetic energy and equilibrium constant are a function of the temperature and are not affected by the addition of the catalyst.
Question 5
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Oxygen is liberated on heating

A
zinc oxide

B
manganese dioxide

C
mercuric oxide

D
magnesium oxide

Solution

Oxygen is liberated on heating mercuric oxide.
HgO is an unstable oxide and breaks down on heating to liberate free oxygen.
2HgO(s) + heat 2Hg(l) + O₂(g)
Question 6
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When iron nails are placed in the blue coloured solution of copper sulphate, the solution turns green. Which type of chemical reaction does it represent?

A
Decomposition

B
Displacement

C
Combination

D
Isomerisation

Solution

When iron nails are placed in the blue coloured solution of copper sulphate, displacement reaction takes place.
Iron being more reactive displaces copper from its salt.
Question 7
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Which of the following options is incorrect about oxidation?

A
Addition of an electronegative element

B
Increase of positive valence

C
Gain of electrons

D
Removal of hydrogen

Solution

Oxidation is the process of loss of electrons.
Question 8
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Which of the following can be considered as a weak electrolyte?

A
NaCI

B
HCI

C
CH₃COOH

D
K₂SO₄

Solution

Acetic acid (CH₃COOH) is considered as a weak electrolyte because it dissociates partially in its aqueous solution to form ions.
Question 9
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In a redox reaction H₂ + F₂ 2HF, the number of electrons involved in the conversion is

A
0

B
2

C
4

D
5

Solution

In the redox reaction H₂ + F₂ 2HF,

Oxidation half reaction:

Reduction half reaction:

Therefore, the number of electrons transferred in the reaction is 2.
Question 10
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Which of the following are redox reactions?

I. Cu + 2H₂SO₄ CuSO₄ + 2H₂O + SO₂
II. BaCI₂ + H₂SO₄ BaSO₄ + 2HCI
III. Zn + H₂SO₄ ZnSO₄ + H₂
IV. 2KNO₃ + H₂SO₄ 2HNO₃ + K₂SO₄

A
II and IV only

B
I, II and III only

C
I and III only

D
I and IV only

Solution

Reactions I and III are redox reactions.
In reaction I, Cu is getting oxidised (oxidation state changes from 0 to +2) and S is getting reduced (oxidation state changes from +6 to +4).
In reaction III, Zn is getting oxidised (oxidation state changes from 0 to +2) and H⁺ is getting reduced (oxidation state changes from +1 to 0).
Question 11
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The characteristic feature of an oxidising agent is that it always

A
gains electrons

B
gets oxidised in a redox reaction

C
contains oxygen

D
is a non-metal

Solution

The characteristic feature of an oxidising agent is that it always gains electrons in a redox reaction and gets reduced.
Question 12
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A solution of ammonium chloride in water

A
turns blue litmus red

B
turns red litmus blue

C
does not affect litmus

D
decolourises litmus

Solution

Ammonium chloride is an acidic salt formed by the neutralisation of a weak base by a strong acid. Thus, a solution of ammonium chloride in water turns blue litmus red.
Question 13
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In reaction P₄O₁₀ + 6H₂O 4H₃PO₄, the oxide of phosphorus act as a/an

A
reducing agent

B
catalyst

C
basic anhydride

D
acidic anhydride

Solution

P₄O₁₀, known as phosphorous pentoxide, is formally an anhydride form of phosphoric acid. Anhydrides are known to react with water to form the parent acid compound. Thus, phosphorus pentoxide reacts with water to give phosphorus acid.
Question 14
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Consider the following reaction:

C(s) + O₂(g) CO₂(g) + 94.3 kcal

Which of the given statements is/are true about the reaction?
I. One mole of CO₂ is produced for every two moles of oxygen consumed.
II. The reaction is endothermic.
III. The reaction is exothermic.

A
I and II

B
Only II

C
Only III

D
I and III

Solution

C(s) + O₂(g) CO₂(g) + 94.3 kcal
The above reaction is exothermic because it is accompanied by the evolution of heat.
Question 15
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When chlorine gas is passed through cold and dilute alkali, the following reaction occurs:

CI₂ + 2OH^- OCI^- + CI^- + H₂O

In this reaction, chlorine undergoes

A
only reduction

B
both oxidation and reduction

C
only oxidation

D
No change in oxidation state

Solution

It is a disproportionation reaction as Cl₂ is undergoing both oxidation and reduction.
Cl₂ + 2e^- 2Cl^- (Reduction)
Cl₂+ 4OH^- 2ClO^- + 2H₂O (Oxidation)
Question 16
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In which of the following ions does chlorine have the the oxidation state of +5?

A
CIO₄^–

B
CIO₃^–

C
CI₂O₇

D
CIO^–

Solution

In CIO₃^– ion, the oxidation state of chlorine is +5.

1. CIO₄^–
x – 8 = -1
x = - 1 + 8 = +7

2. CIO₃^–
x - 6 = -1
x = - 1 + 6 = +5

3. CI₂O₇
2x – 14 = 0
x = 14/2 = 7

4. CIO^–
x – 2 = -1
x = - 1 + 2 = +1
Question 17
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In solution, a double salt furnishes

A
two different cations, other than H⁺

B
two different anions other than OH^–

C
either two different cations other than H⁺ or two different anions other than OH^–

D
two cations and two anions

Solution

In solution form, a double salt furnishes either two different cations other than H⁺ or two different anions other than OH^–.
Question 18
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During electrolysis, the reaction at the anode is

A
oxidation

B
reduction

C
hydrolysis

D
hydration

Solution

The apparatus used for electrolysis is an electrolytic cell.
The reaction occuring at the anode (positive electrode) is oxidation and the reaction occuring at the cathode (negative electrode) is reduction.
Question 19
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Which of the following options is incorrect regarding oxidation number?

A
Oxidation number of P in PO₄^–3 is +5.

B
Oxidation number of S in H₂SO₄ is +6.

C
Oxidation number of Mn in KMnO₄ is –7.

D
Oxidation number of C in CH₄ is –4.

Solution

KMnO₄ is a neutral compound.
So, oxidation number of Mn = 1 + Mn + (-2)4 = 0
Mn - 7 = 0
Mn = 7
So, the oxidation number of Mn in KMnO₄ is +7.