Chemical Reactions And Equations Test

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Chemical Reactions And Equations Test - 3

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Weekly Quiz Competition

Question 1
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A chemical change involves the formation of a new substance, with properties different from those of the reactants. Which among the following is not a chemical change?

A
Souring of milk to form curd

B
Burning of a magnesium ribbon in air

C
Emitting of light by a red hot platinum wire

D
Rusting of iron in the atmosphere

Solution

Platinum is a relatively inert metal and does not get oxidised in the air, even when heated to very high temperatures. Therefore, the emission of light by heating the platinum wire is a physical change.
Question 2
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Magnesium burns in air with a dazzling white flame and the reaction may be represented as:

The reaction may be classified as a/an

A
combination reaction

B
oxidation reaction

C
exothermic reaction

D
All of the above

Solution

The given reaction is a combination reaction involving the combination of magnesium and oxygen to form magnesium oxide.
Since the combination of a substance with oxygen is oxidation of the substance, it is also an oxidation reaction.
All combination reactions are exothermic.
Hence, option 4 is the correct answer.
Question 3
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Which is the reducing agent in the thermite reaction carried out for repairing of the railway tracks?

A
Iron oxide

B
Aluminium metal

C
Aluminium oxide

D
Iron metal

Solution

Thermite reaction is the reduction of iron oxide by aluminium to form iron.

The reaction is highly exothermic and the iron formed is in the molten state, which fills the cracks in the railway track.

Aluminium metal gets oxidised and is the reducing agent.
Question 4
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Neutralisation reaction is an example of

A
displacement reaction

B
double displacement reaction

C
decomposition reaction

D
combination reaction

Solution

In neutralisation reaction, a base reacts with an acid to form salt and water.
For example,
NaOH + HCl NaCl + H₂O
It agrees with the format of double displacement reaction which is AB + CD AC + BD.
Question 5
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Directions: Analyse the given chemical change and select the correct option in relation to this reaction.

A
The reaction is endothermic.

B
A precipitate is formed.

C
The reaction is exothermic.

D
There is a change in colour.

Solution

The given reaction is endothermic and the test tube gets cold because of the heat absorbed.
Question 6
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What happens when the potassium iodide solution is added to a solution of lead nitrate?

A
White precipitate of lead iodide is formed.

B
Yellow precipitate of lead iodide is formed.

C
Red precipitate of lead iodide is formed.

D
Black precipitate of lead iodide is formed.

Solution

When a solution of potassium iodide is added to lead nitrate solution, then a precipitate is formed. This precipitate is of lead iodide which is yellow in colour.
Pb(NO₃)₂ + 2KI 2KNO₃ +
Question 7
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Analyse the chemical reagents and the suggested containers for storing them.

Which of the following combinations are not recommended?

A. AgNO₃ in copper vessel
B. CuSO₄ in silver vessel
C. Cu(NO₃)₂ in an iron container
D. H₂SO₄ in Al vessel

A
A, C and D

B
B, C and D

C
A and C

D
A, B and C

Solution

Only 'B' is a valid suggestion as CuSO₄ can be safely stored in a silver vessel as no chemical reaction will occur in this case.
Silver being less reactive than copper cannot displace Cu from its solution.
Salt solutions of less reactive metals cannot be stored in containers made of more reactive metals as displacement reactions will take place.
Question 8
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Analyse the two statements given below and select the correct option.

Statement I: Melting of ice is an endothermic process.
Statement II: Freezing of water is exothermic.

A
Both statements I and II are correct and statement II is the correct reason for I.

B
Both statements I and II are correct, but statement II is not the correct reason for I.

C
Statement I is correct, but statement II is incorrect.

D
Both statements I and II are incorrect.

Solution

Melting of ice is endothermic as energy is required to overcome the intermolecular attractions that hold the molecules together in ice.
Freezing of water is exothermic as on cooling, the molecules of water release energy to the surroundings and the intermolecular forces become more significant so that it now exists in the solid state.
Hence, both statements I and II are correct, but statement II is not the correct reason for I.
Question 9
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Sulphur burns in air to form its oxide and the reaction can be represented by the following equation:

Which of the following statements in relation to this reaction is incorrect?

A
It is a synthesis reaction.

B
The process is exothermic.

C
It is a redox reaction.

D
The oxide formed is acidic and dissolves in water to form sulphuric acid.

Solution

Statement (4) is only partially true. Sulphur dioxide is an acidic oxide which dissolves in water to form sulphurous acid, not sulphuric acid.

All the other statements are correct.
Question 10
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Which of the following processes results in a chemical change?

A
Distillation

B
Filtration

C
Oxidation

D
Evaporation

Solution

Oxidation is a chemical process and results in the formation of a new substance having properties different from those of the reactants.

Question 11

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The chemical reactions and its corresponding observable features are listed below.

a. Change in temperature	(i) Magnesium reacting with dilute sulphuric acid
b. Evolution of a gas	(ii) Potassium iodide reacting with lead nitrate
c. Formation of a precipitate	(iii) Sulphur dioxide gas reacting with acidified potassium dichromate solution
d. Change in colour	(iv) Zinc granules reacting with dilute sulphuric acid

Choose the most appropriate code from among the options given below:

a - (iii), b - (iv), c - (i), d - (ii)

a - (iv), b - (i), c - (ii), d - (iii)

a - (i), b - (iv), c - (iii), d - (ii)

a - (iv), b - (ii), c - (iii), d - (i)

Solution

a. Every reaction involves energy changes and subsequent change in temperature.
b. Magnesium reacting with dilute sulphuric acid will release hydrogen gas.
c. Potassium iodide reacting with lead nitrate will form a yellow precipitate of PbI₂.
d. Sulphur dioxide gas reacting with acidified potassium dichromate solution will change the orange colour of K₂Cr₂O₇ to green.

Question 12
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Consider the following hypothetical reaction and fill in the blanks by choosing the correct option.

x + y - z x - z + y

In the given chemical reaction, old bonds between _________ are broken and new bonds between _________ are formed.

A
x and y; x and z

B
x and z; y and z

C
y and z; x and y

D
y and z; x and z

Solution

During a chemical change, the atoms are never created or destroyed, they are only rearranged.
In the given reaction, the bonds between y and z break and a new compound is formed by the association of x and z.
Question 13
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What is the visual indication that a chemical change has occurred when an aqueous solution of sodium sulphate is mixed with that of barium chloride?

A
Evolution of gas

B
Change in colour of the solution

C
Absorption of heat

D
Formation of a precipitate

Solution

The following reaction takes place:
Na₂SO₄(aq) + BaCl₂(aq) NaCl(aq) + BaSO₄(aq)
Barium sulphate formed is insoluble and settles down as a white precipitate.
Question 14
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Quicklime combines with water to form 'X'. Identify 'X' and indicate the energy change involved.

A
Limewater; the reaction is exothermic.

B
Slaked lime; the reaction is endothermic.

C
Lime; the reaction is exothermic.

D
Lime; the reaction is endothermic.

Solution

The balanced chemical equation is as follows::
CaO(s) + H₂O(l) Ca(OH)₂(aq)
The reaction is exothermic and the vessel gets heated.
Question 15
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A solution of calcium hydroxide is used for whitewashing the walls. After two to three days of whitewashing, the walls start shining due to the formation of the compound:

A
CaO

B
CaCO₃

C
CaSO₄

D
Ca(HCO₃)₂

Solution

Ca(OH)₂(aq) + CO₂(g) CaCO₃(s) + H₂O(l)

The white shine on the walls is due to the formation of calcium carbonate formed by the reaction of slaked lime with atmospheric carbon dioxide.
Question 16
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Which of the following reactions requires the highest temperature to occur?

A
N₂+ O₂2NO

B
2NO + O₂2NO₂

C
NH₄NO₂ N₂+ 2H₂O

D
4NO₂ + 2H₂O + O₂4HNO₃

Solution

N₂ gas is inert and does not react under ordinary conditions as the NN bond is very strong and has a very high bond enthalpy.
Hence, the 1^st reaction will require the highest temperature to occur.
Question 17
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Consider the following reaction:

Al(s) + Fe₂O₃(s) Al₂O₃(s) + Fe(s)

Which of the following statements is not correct about the given reaction?

A
It is a redox reaction.

B
It is the thermite reaction.

C
It is a decomposition reaction.

D
It is a displacement reaction.

Solution

This reaction is not a decomposition reaction. It involves the reduction of iron oxide to iron by using aluminium as the reducing agent. It is called the thermite reaction and is highly exothermic. It is used to repair the cracks in the railway tracks. It involves the displacement of iron from its oxide by aluminium.
Question 18
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When the reaction Pb(NO₃)₂ PbO + NO₂+ O₂ is balanced, the coefficients of the reactants and products in the balanced reaction will respectively be:

A
4, 2, 1, 2

B
2, 2, 4, 1

C
2, 4, 1, 2

D
4, 2, 2, 2,

Solution

2Pb(NO₃)₂2PbO + 4NO₂ + O₂
No. of Pb on both sides = 2
No. of N on both sides = 4
No. of O on both sides = 12
Question 19
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Consider the following chemical reaction:

HNO₃(aq) + KOH(aq) KNO₃(aq) + H₂O(l)

The given reaction is an example of

A
neutralisation

B
double displacement

C
neutralisation and double displacement

D
combination

Solution

This is a reaction of neutralisation of KOH by nitric acid and also involves the exchange of ions between the acid and the base.
Question 20
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Consider the following statements about redox reactions:

(i) A substance is said to be reduced if it gains electrons during a reaction.
(ii) A substance is said to be oxidised if it gains hydrogen during a reaction
(iii) A substance is said to be reduced if it loses oxygen during a reaction.
(iv) A substance is said to be reduced if it gains hydrogen during a reaction.

Which of the given statements is/are correct?

A
(i) and (ii)

B
(ii) and (iii)

C
(iii) only

D
(i), (iii) and (iv)

Solution

Only statement (ii) is incorrect because gain of hydrogen is reduction, and not oxidation.