Chemical Reactions Test

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Chemical Reactions Test - 6

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following is a chemical change?

A
Melting of ice

B
Burning of sulphur

C
Melting of wax

D
Magnetisation of iron

Solution

Chemical change is any change that results in the formation of a new chemical substance. Burning of sulphur is a chemical change as it reacts with oxygen to form sulphur dioxide gas.
S(s) + O₂(g) –--> SO₂(g)
Question 2
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What will happen if temperature of 1 kg of water is raised from 30^o to 140^oC?

I. There will be a change in the physical state of the substance.
II. It goes through a chemical change.
III. All the heat supplied does not contribute to the temperature rise.
IV. The boiling point of water will depend on the atmospheric pressure.

A
I and II

B
I, III and IV

C
II, III and IV

D
II and III

Solution

When the temperature of 1 kg of water is raised from 30^oC to 140^oC, a physical change of state occurs and water vapourizes to steam.
The change of state requires latent heat of vapourization.
Also, the boiling point of water is directly proportional the atmospheric pressure.
Question 3
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Chemical change does not take place in case of

A
souring of milk into curd

B
burning of magnesium ribbon in air

C
emitting of light by a red hot platinum wire

D
rusting of iron in atmosphere

Solution

Chemical change does not take place in case of emission of light by a red hot platinum wire.Platinum is a noble metal and does not get oxidised on burning in the air.
On heating, it becomes red hot, but does not get oxidised.
Question 4
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Which of the following represents a chemical change?

A
Evaporation of water

B
Sublimation of iodine

C
Heating a platinum wire in Bunsen flame

D
Heating of FeS powder

Solution

Heating of iron sulphide powder represents a chemical change.
Chemical change is any change that results in the formation of new chemical substances.
Heating of iron sulphide in air is a chemical change.
FeS(s) + O₂(g) → Fe(s) + SO₂(g)
Question 5
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Which of the following processes causes a chemical change?

A
Distillation

B
Filtration

C
Oxidation

D
Evaporation

Solution

A chemical change involves the creation of a new substance from two or more reactants. After a chemical change occurs, the new substance, called a product, has a different chemical composition than the original materials.
Oxidation is one example of a chemical change. The substance is oxidised by a loss of electrons and forms a new substance.
Question 6
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What is generally affected in a chemical change?

A
Nucleus

B
Electron

C
Neutron

D
Proton

Solution

Chemical changes are generally brought about by the transfer or sharing of the electrons. The electrons of the valence shell participate in the chemical reactions.
Question 7
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Which of the following is a reduction reaction?

A
Fe²⁺ Fe³⁺ + e^–

B
2I^-– 2e^– I₂

C
Sn²⁺ Sn⁴⁺ + 2e^–

D
Cu²⁺ Cu^o – 2e^–

Solution

Cu²⁺ Cu^o – 2e^– is a reduction reaction because oxidation state changes from + 2 to 0.
Question 8
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In the ordinary fire extinguisher, carbon dioxide is generated by the reaction of

A
marble powder and dilute HCI

B
limestone and dilute H₂SO₄

C
sodium bicarbonate and dilute H₂SO₄

D
magnetite and dilute HCI

Solution

In an ordinary fire extinguisher, carbon dioxide is generated by the reaction of sodium bicarbonate and dilute H₂SO₄.
The reaction occuring is a neutralization reaction and the large volumes of CO₂ evolved envelop the burning substance and cut off the supply of oxygen. The water produced helps to bring down the temperature of the burning substance below the ignition temperature and therefore puts out the fire.
Question 9
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When a small amount of manganese dioxide is added to hydrogen peroxide, oxygen is evolved. This is an example of

A
reduction

B
oxidation

C
double decomposition

D
decomposition

Solution

When a small amount of manganese dioxide is added to hydrogen peroxide, oxygen is evolved. This is an example of a decomposition reaction.
H₂O₂ decomposes to H₂O and O₂; MnO₂ acts a catalyst in the reaction.
Question 10
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Which of the following is an example of photolysis reaction?

A
Fe + S FeS

B
PCl₃ + Cl₂ PCl₅

C
CaO + CO₂ CaCO₃

D
2AgCl 2Ag + Cl₂

Solution

Photolysis is a decomposition chemical reaction brought about by utilising light energy.
For example, 2AgCl Ag + Cl₂
Question 11
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Which of the following reactions involves neutralization as well as precipitation?

A
Reaction between baking powder and H₂SO_4.

B
Reaction between barium chloride and Na₂SO_4.

C
Reaction between silver nitrate and HCl.

D
Reaction between slaked lime and H₂SO_4.

Solution

The reaction between slaked lime and H₂SO₄ involves neutralisation as well as precipitation.
Question 12
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Balancing of chemical equation is done for compliance with

A
law of conservation of mass

B
law of constant proportion

C
law of reciprocal proportion

D
All of the above

Solution

Chemical equations are balanced in order to comply with the law of conservation of mass.
Law of conservation of mass states that atoms (matter) are not destroyed in any physical or chemical process.
Therefore the number of atoms of each element on both the sides of the equation is always equal.
Question 13
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Consider the following partial ionic reaction:
S₂ + 32H₂O 8SO₄^-+ 64H⁺ + 48e^-
The equivalent weight of sulphur is

A
32/6

B
32/48

C
32/8

D
32

Solution
Question 14
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In the given ionic reactions, which one of the ions is getting oxidized?

Cu²⁺(aq) + 2e^- Cu(s)
2Cl^-(aq) Cl₂(g)+ 2e^-

A
Cu²⁺ ion

B
Cl^- ion

C
Both Cu²⁺ and Cl^- ions

D
Neither of the two

Solution

Cu⁺² is getting reduced by gaining electrons and the oxidation number decreases from + 2 to 0.
Cl^-¹ is getting oxidised by losing electrons and the oxidation number increases from - 1 to 0.
Question 15
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Which one of the following electrolytes contains the largest number of ions?

A
50g K₂SO₄(molecular mass 174)

B
50g NaCI (molecular mass 58.5)

C
50g NH₄CI (molecular mass 53.5)

D
50g CaCI₂ (molecular mass 111)

Solution
Question 16
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Which of the following is the best reducing agent?

A
F^-

B
CI^-

C
Br^-

D
I^-

Solution

I^- is the best reducing agent because of its larger size; it loses its electron and gets oxidised to I₂and acts as a reducing agent.
Question 17
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Which of the following is not a redox reaction?

A
Br₂ + 2KI 2KBr + I₂

B
3Cu + 8HNO₃ 3Cu(NO₃)₂ + 2NO + 4H₂O

C
CaO + 2HCl CaCl₂ + H₂O

D
MnO₂ + 4HCl MnCl₂ + Cl₂ + 2H₂O

Solution

CaO + 2HCl CaCl₂ + H₂O is a not a redox reaction because none of the elements is undergoing a change in its oxidation state.
Question 18
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In the reaction: Zn + H₂SO₄ ZnSO₄ + H₂, zinc undergoes

A
oxidation

B
reduction

C
hydrogenation

D
dehydrogenation

Solution

In the reaction: Zn + H₂SO₄ ZnSO₄ + H₂,zinc undergoes oxidation because its oxidation state increases from 0 to +2.
Question 19
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The oxidation number of sulphur in SO₄^2– is

A
two

B
one

C
six

D
four

Solution

The oxidation number of sulphur in SO₄^2-= x + (- 8) = - 2
x = - 2 + 8
x = 6
Question 20
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In the formula of aluminium sulphate, what does the subscript '3' indicate?

A
Number of aluminium ions

B
Number of aluminium atoms

C
Number of sulphate ions

D
Number of oxygen atoms

Solution

In the formula of aluminium sulphate, i.e. Al₂(SO₄)₃, subscript '3' indicates the number of sulphate ions present in one formula unit of the compound.