Physical and Chemical Changes Test

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Physical and Chemical Changes Test - 1

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Question 1
1 / -0

Mg + O₂ 'X'
'X' + H₂O 'Y'
What are 'X' and 'Y' in the above two reactions?

A
Magnesium oxide and water

B
Magnesium oxide and magnesium hydroxide

C
Magnesium and oxygen

D
Water and magnesium hydroxide

Solution

Magnesium, when burnt in air, reacts with oxygen resulting in formation of magnesium oxide which when dissolved in water forms magnesium hydroxide as per the following reactions:

MgO +
So, the substance 'X' is magnesium oxide and 'Y' is magnesium hydroxide.
Question 2
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While working in a lab, Mary dropped a blade in a solution of copper sulphate. She observed a change in the colour of the solution from

A
blue to colourless

B
red to blue

C
blue to green

D
green to blue

Solution

Copper sulphate solution is blue in colour. A blade is made up of iron. When iron is dropped in this solution, it reacts with copper sulphate resulting in the formation of iron sulphate and copper as per the reaction:

So, the colour change is from blue to green.
Question 3
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Complete the following reaction:

Copper sulphate solution + Iron ? + Copper

A
Sulphuric acid

B
Iron oxide

C
Iron sulphate

D
Hydrochloric acid

Solution

Copper sulphate solution is blue in colour. When an iron object is dropped into this solution, it reacts with copper sulphate as per the following reaction:

The blue colour of the solution changes to green due to the formation of ferrous sulphate (FeSO₄^₎.
Question 4
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Which gas appears as bubbles on addition of vinegar in baking soda?

A
Oxygen

B
Nitrogen

C
Carbon dioxide

D
Argon

Solution

Chemical name of vinegar is acetic acid and that of baking soda is sodium hydrogen carbonate. The reaction between acetic acid and sodium hydrogen carbonate results in the formation of carbon dioxide gas and other products.
Question 5
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Iron is coated with a layer of ________ to protect it from rusting.

A
carbon

B
chromium

C
bromine

D
fluorine

Solution

Iron is reactive towards atmospheric air and water vapour. So, to prevent iron objects from rusting, they are coated with a layer of zinc or chromium, which prevents the iron from getting rusted out.
Question 6
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Ships suffer a lot of damage because of rusting. Which of the following helps in slowing down the rusting of ships?

A
Ships being made of iron.

B
Ships being painted from outside.

C
A part of the ship remaining underwater.

D
Presence of salt in sea water.

Solution

Ships are made of iron. Iron being a reactive element reacts with atmospheric oxygen in the presence of moisture to form a layer of rust. Presence of salt in the sea water increases the rate of rusting.
A part of the ship remaining underwater the sea water does not prevent it from rusting.
Rusting can be prevented by covering the ship with a coat of paint which prevents the contact between iron and the air and moisture.
Question 7
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Which of the following features is not related to a physical change?

A
Temporary nature of the change

B
Reversible nature of the change

C
Change in chemical properties

D
Change in shape, state or other physical properties

Solution

A physical change is generally temporary and reversible and involves a change in the shape, state or other physical properties of a substance.
It does not bring about any change in the chemical composition of the substance.
Question 8
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Which of the following processes is not a chemical change?

A
Photosynthesis

B
Digestion

C
Respiration

D
Evaporation

Solution

Photosynthesis, digestion and respiration are the processes which result in the formation of a new substance, different from the reacting species. Hence, each of this process is categorised as a chemical change.

Evaporation is a process which changes the state of a substance without bringing about any change in the chemical composition of the substance. Therefore, evaporation is a physical change.
Question 9
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The presence of ______ prevents the rusting of iron.

A
aluminium

B
oxygen

C
water

D
zinc

Solution

Rusting of iron can be prevented by coating iron with a layer of zinc.
Question 10
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Which of the following is the standard test for carbon dioxide?

A
Burning of fuel

B
Bubbling on addition of vinegar to baking soda

C
Turning of limewater milky

D
Baking of cake

Solution

The best test to check the evolution of carbon dioxide is to pass it through limewater, which turns it milky due to the formation of insoluble calcium carbonate.
Question 11
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When carbon dioxide is passed through limewater, it turns milky due to the formation of

A
lithium carbonate

B
potassium carbonate

C
sodium carbonate

D
calcium carbonate

Solution

When carbon dioxide is passed through limewater, it turns milky due to the formation of calcium carbonate.
Question 12
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Which of the following is not a chemical change?

A
Magnetisation of a bar of steel

B
Burning of petrol

C
Fermentation of cane juice

D
Butter turning rancid

Solution

Magnetisation of a bar of steel is not a chemical change.
Question 13
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Which of the following statements is/are false?

a. Charring of sugar into charcoal by strong heating is a physical change.
b. New medicines are produced by a chain of chemical reactions.
c. Formation of curd is an example of a chemical change.

A
Only a

B
Only b

C
Only c

D
Both b and c

Solution

Charring of sugar into charcoal by strong heating is a chemical change.
On heating, water evaporates and caron is left behind as a black mass.
Hence, statement (a) is false.
Question 14
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Consider the following reaction:
2KClO₃ 2KCl + O₂
In this reaction, potassium chlorate gives potassium chloride and oxygen. How many atoms of oxygen are present in the reactant of the given reaction?

A
6

B
5

C
4

D
3

Solution

In this equation, there are 6 atoms of oxygen present in the reactants and 2 atoms in the products.
Question 15
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Soft drinks contain carbon dioxide and hydrogen. Why are they sour in taste when neither hydrogen nor carbon dioxide is sour?

A
Because they contain hydrochloric acid

B
Because they contain carbonic acid

C
Because they contain carboxylic acid

D
Because they contain sulphuric acid

Solution

Soft drinks are sour because hydrogen and carbon dioxide react to form carbonic acid, which is sour in taste.