Physical And Chemical Changes Test

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Physical And Chemical Changes Test - 5

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Weekly Quiz Competition

Question 1
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If we keep moistened iron nails for a few days, the iron nails get covered with a reddish-brown substance, which is different from iron. Which of the following is/are not the change(s) that take(s) place?

a. The state as well as the composition of iron changed.
b. The changes that took place were reversible.
c. A new substance was formed.

A
Only a

B
Only a and b

C
Only b

D
Only b and c

E
Only c

Solution

This is the correct option as the change that took place was not reversible. It was irreversible.
Question 2
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Iron objects, such as the wheels of a bicycle, are coated with which of the following metals to give them a shining appearance?

A
Aluminium

B
Lead

C
Nickel

D
Copper

E
Magnesium

Solution

This is the correct option. Iron objects are coated with nickel to give them a shining appearance. Shine of Nickel is more durable whereas many other metals eventually corrode and become dull.
Question 3
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Identify the incorrect statement(s).

Statement I: All physical changes are spontaneous, but chemical changes have to be induced.
Statement II: All changes, physical as well as chemical, involve energy exchanges.

A
Only I

B
Only II

C
Both I and II

D
None

Solution

Statement I is incorrect as spontaneity of a process depends on the conditions available. Many physical as well as chemical processes are spontaneous under standard conditions. For example, evaporation of water is spontaneous and so is the reaction of Na metal with the water vapour in the air. Statement II is correct as both physical and chemical processes involve energy changes.
Question 4
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Pick the odd one out with respect to the type of reaction that would take place between the following substances:

A
Al, FeSO₄

B
BaCl₂, Na₂SO₄

C
Pb(NO₃)₂, KI

D
AgNO₃, NaCl

Solution

The reaction between Al and FeSO₄ is an example of single displacement reaction, where Al displaces Fe from its salt solution.

All the other reactions are examples of double displacement reactions, where an exchange of ions takes place between the reactant species.

Question 5

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Match the following:

A. BaCl₂ + Na₂SO₄ BaSO₄ + 2NaCl	(i) Combination reaction
B. Mg + H₂O MgO + H₂	(ii) Double displacement reaction
C. 2KClO₃ 2KCl + 3O₂	(iii) Decomposition reaction
D. C + O₂ CO₂	(iv) Displacement reaction

A - (ii), B - (i), C - (iv), D - (ii)

A - (iv), B - (i), C - (ii), D - (i)

A - (ii), B - (iv), C - (iii), D - (i)

A - (iii), B - (iv), C - (ii), D - (i)

Solution

(A) BaCl₂ + Na₂SO₄ BaSO₄ + 2NaCl	(ii) Double displacement reaction
(B) Mg + H₂O MgO + H₂	(iv) Displacement reaction
(C) 2KClO₃ 2KCl + 3O₂	(iii) Decomposition reaction
(D) C + O₂ CO₂	(i) Combination reaction

Question 6
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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 7
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Which of the following is not a chemical change?

A
Blackening of silver ornaments

B
Burning of a candle

C
Formation of water vapour

D
Browning of an apple

Solution

The conversion of water into vapour is a physical change, as no new substance with different chemical properties is formed.
Question 8
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When copper turnings are added to a clear solution of silver nitrate, a greyish deposit of silver is observed after some time. Silver gets precipitated and copper (II) nitrate is also formed. The reaction is an example of __________ reaction and ________ is more reactive than ________.

A
displacement, copper, silver

B
decomposition, copper, silver

C
decomposition, silver, copper

D
displacement, silver, copper

Solution

The chemical equation for the reaction is Cu (s) + 2AgNO₃(aq) 2Ag (s) + Cu(NO₃)₂(aq).
In the given reaction, a metal (copper) is replacing another metal (silver) from the solution of its compound. Hence, the given reaction is an example of a displacement reaction. Copper replaces silver from the solution of its compound. Hence, copper is more reactive than silver.
Question 9
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Zinc oxide (ZnO) reacts with carbon (C) to produce zinc (Zn) and carbon monoxide (CO). The balanced chemical equation for the given reaction is ZnO (s) + C (s) Zn (s) + CO (g). Which of the following substances is reduced in the given reaction?

A
ZnO

B
C

C
CO

D
Zn

Solution

The given reaction is an example of a redox reaction. In a redox reaction, the substance that either gains oxygen or loses hydrogen is oxidised and the substance that loses oxygen or gains hydrogen is reduced. In the given reaction, zinc oxide (ZnO) loses oxygen to form zinc (Zn). Hence, ZnO is reduced in the given reaction.
Question 10
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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 11
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Consider the following reaction:

MnO₂ + 4HCl MnCl₂ + Cl₂ + 2H₂O

Which of the following is getting oxidised in this reaction?

A
MnO₂

B
Cl₂

C
HCl

D
H₂O

Solution

In this reaction, hydrogen chloride is getting oxidised to form chlorine gas.
Question 12
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Which of the following statements is true about the reaction of copper turnings with the silver nitrate solution?

A
The colour of the copper turnings kept in the silver nitrate solution is same as the colour of those kept aside.

B
An effervescence is observed.

C
The colour of the solution changes to blue.

D
There is no change in the colour of the solution.

Solution

The colour of the solution changes to blue as copper displaces silver from the solution to form copper nitrate.
Question 13
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Which of the following statements is not true about a substance that goes rancid?

A
Its smell changes.

B
Its taste changes.

C
Its colour changes.

D
It reduces in mass.

Solution

Rancidity is a term generally used to denote unpleasant odours, colour change and flavours in foods resulting from deterioration in the fat or oil portion of a food. There is no change in the mass observed, which is in agreement with the law of conservation of mass.
Question 14
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Suppose, a reaction takes place between magnesium and oxygen to form magnesium oxide. Where will magnesium oxide be represented in the chemical equation?

A
L.H.S. of the arrow

B
R.H.S. of the arrow

C
Top of the arrow

D
Down the arrow

Solution

The reaction between Mg and oxygen is represented as:
2Mg + O₂ 2MgO
Thus, MgO is the product and it is present on R.H.S of the arrow.
Question 15
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Which of the following phenomena is not an indication of a chemical change?

A
Evolution of a gas

B
Change in shape

C
Change in temperature

D
Change in colour

Solution

Change in the shape of a substance does not indicate that a chemical change has taken place.