• Physical and Chemical Changes (Class VII)
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Physical and Chemical Changes (Class VII)

Description: Physical and Chemical Changes
Number of Questions: 15
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Tags: Physical and Chemical Changes Rusting of Iron Crystallisation Differentiating Materials on the Basis of Floatation Physical Changes and Its Characteristics Identifying Chemical Changes Common Types of Chemical Changes Rusting and Its Prevention
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Which of the following statements is/are false?

a. Some chemical substances can be obtained in pure state by the process of crystallisation. b. The product formed when a substance dissolves in a liquid is known as a solution. c. In a chemical reaction, the substances responsible for bringing about a chemical change are called products.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: E
Explanation:

This is the correct option as this statement is false. In a chemical reaction, the substances responsible for bringing about a chemical change are called reactants.

Magnesium, when burnt in the presence of oxygen, forms a new product. Which of the following statements is/are false regarding the chemical reaction that took place?

a. On burning in air, magnesium formed magnesium oxide. b. The change that took place was permanent and irreversible. c. No heat or light was evolved.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: E
Explanation:

This is the correct option. Heat and light were evolved when magnesium burnt in air to form magnesium oxide.

Which of the following is not a property of a physical change?

  1. No new substances are formed.

  2. The change is temporary in nature.

  3. The change can be easily reversed by removing the cause of the change.

  4. There cannot be any change in a substance's physical properties.

  5. The composition of substances remains unchanged.

Show answer
Correct Option: D
Explanation:

This is the correct option as this is not a property of a physical change. There may be some change in substance's physical properties like colour, smell, taste, etc.

When carbon dioxide is bubbled through limewater, a new substance is formed. Which of the following is the new substance?

  1. Calcium bicarbonate

  2. Calcium acetate

  3. Calcium gluconate

  4. Calcium hydroxide

  5. Calcium carbonate

Show answer
Correct Option: E
Explanation:

This is the correct option. When carbon dioxide is bubbled through limewater, calcium carbonate is formed.

Ca(OH)2 + CO2 --> CaCO3 + H2O

Chemical reactions are very important. Which of the following is not done with the help of a chemical reaction?

  1. Extraction of metals from their ores

  2. Magnetisation of an iron bar

  3. Production of new medicines

  4. Preparation of plastics

  5. Preparation of building materials

Show answer
Correct Option: B
Explanation:

This is the correct option as magnetisation of an iron bar is not done with the help of a chemical reaction.

Which of the following is not a property of a chemical change?

  1. Changes are temporary and reversible.

  2. Changes are followed by the formation of a new product.

  3. Changes may give out or absorb heat, light or sound.

  4. Changes are followed by the change in state and composition.

  5. Changes may be followed by the change in colour.

Show answer
Correct Option: A
Explanation:

This is the correct option as this is not a property of a chemical change. Changes are permanent and irreversible.

Which of the following is not an example of a chemical change?

  1. Rusting of iron

  2. Charring of sugar into charcoal

  3. Burning of fuels

  4. Cooking of food

  5. Dissolution of rubber in alcohol

Show answer
Correct Option: E
Explanation:

This is the correct option as dissolution of rubber in alcohol is not an example of a chemical change. It is an example of a physical change.

If sodium carbonate is added to dil. sulphuric acid, sodium sulphate and water are formed, along with the release of a gas. Which of the following gases is released?

  1. Oxygen

  2. Helium

  3. Carbon dioxide

  4. Hydrogen

  5. Nitrogen

Show answer
Correct Option: C
Explanation:

This is the correct option. If sodium carbonate is added to dil. sulphuric acid, sodium sulphate and water are formed, along with the release of carbon dioxide.

Na2CO3 + H2SO4 --> Na2SO4 + H2O + CO2  

Iron objects, such as the wheels of a bicycle, are coated with which of the following metals to give them a shining appearance?

  1. Aluminium

  2. Lead

  3. Nickel

  4. Copper

  5. Magnesium

Show answer
Correct Option: C
Explanation:

This is the correct option. Iron objects are coated with nickel to give them a shining appearance.

Which of the following statements is/are false?

a. Rusting takes place only if the water and the oxygen come in contact with iron at the same time. b. The process by which plants prepare their food is an example of a physical change. c. The state of ice changes from solid to liquid on heating.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: C
Explanation:

This is the correct option as this statement is false. The process by which plants prepare their food is an example of a chemical change.

Which of the following are added into molten iron in fixed amounts to make an alloy called stainless steel?

a. Copper b. Carbon c. Chromium d. Aluminium

  1. Only a and b

  2. Only a and c

  3. Only a and d

  4. Only b and c

  5. Only b and d

Show answer
Correct Option: D
Explanation:

This is the correct option. Carbon and chromium are added into molten iron in fixed amounts to make an alloy called stainless steel.

Which of the following is not an example of a physical change?

  1. Glowing of an electric bulb

  2. Fermentation of cane juice, fruit juice, etc.

  3. Dissolution of sulphur in carbon disulphide

  4. Freezing of water in a fridge

  5. Dissolution of resin in alcohol

Show answer
Correct Option: B
Explanation:

This is the correct option. Fermentation of cane juice, fruit juice, etc. is irreversible and thus, is not an example of a physical change.

Magnesium oxide, when dissolved in water, forms a new product. Which of the following is the new product thus formed?

  1. Magnesium hydroxide

  2. Magnesium chloride

  3. Magnesium sulphate

  4. Magnesium acetate

  5. Magnesium bromide

Show answer
Correct Option: A
Explanation:

This is the correct option. When magnesium oxide is dissolved in water, magnesium hydroxide is formed.

MgO  +  H2O --> Mg(OH)2  

Match the following ||| |---|---| |a. Crystallisation|1. It is the process of coating thin layer of zinc on iron sheets.| |b. Galvanisation|2. It is the process due to which iron rusts in the moist air. | |c. Rusting|3. It is the process of obtaining crystals from a hot saturated solution. |

  1. a-3, b-1, c-2

  2. a-3, b-2, c-1

  3. a-1, b-3, c-2

  4. a-1, b-2, c-3

  5. a-2, b-1, c-3

Show answer
Correct Option: A
Explanation:

This is the correct option. Crystallisation is the process of obtaining crystals from a hot saturated solution. Galvanisation is the process of coating thin layer of zinc on iron sheets. Rusting is the process due to which iron rusts in the moist air.

If we keep moistened iron nails for a few days, the iron nails get covered with a reddish-brown substance, that is different from iron. Which of the following is/are not the changes 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.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: C
Explanation:

This is the correct option as the change that took place was not reversible. It is irreversible.

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