NCERT Class VII Science Solutions: Chapter 6-Physical and Chemical Changes Part 3

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SHORT ANSWER QUESTIONS

Question 14:

Match the items of Column I with the items of Column II.

Match the Items of Column I with the Items of Column II. (Q)
Match the items of Column I with the items of Column II. (Q)

Column I

Column II

Large crystals

Turns lime water milky

Depositing a layer of zinc on iron

Physical change

Souring of milk

Rust

Carbon dioxide

Sugar candy (Mishri)

Iron oxide

Chemical change

Dissolving common salt in water

Galvanisation

Answer:

Match the Items of Column I with the Items of Column II. (A)
Match the items of Column I with the items of Column II. (A)

Column I

Column II

Large crystals

iv Sugar candy (Mishri)

Depositing a layer of zinc on iron

vi Galvanisation

Souring of milk

v Chemical change

Carbon dioxide

i Turns lime water milky

Iron oxide

iii Rust

Dissolving common salt in water

ii Physical change

Question 15:

Fill in the blanks in the following statements using the words given in the box.

Rusted, colorful, substance, chemical, physical, reversible, iron oxide, object

  1. Making sugar solution is a __________ change.

  2. A physical change is generally___________.

  3. Grinding of wheat grain changes its size. It is a___________ change.

  4. Iron benches kept in lawns and gardens get___________. It is a__________ change because a new ________ is formed.

Answer:

  1. Making sugar solution is a physical change.

  2. A physical change is generally reversible.

  3. Grinding of wheat grain changes its size. It is a physical change.

  4. Iron benches kept in lawns and gardens get rusted. It is a chemical change because a new substance is formed.

Question 16:

Classify the following processes into physical or chemical changes:

  1. Beating of aluminium metal to make aluminium foil.

  2. Digestion of food.

  3. Cutting of a log of wood into pieces.

  4. Burning of crackers.

Answer:

(i) and (iii) are physical changes

(ii) and (iv) are chemical changes

Image of physical change vs chemical change

Image of Physical Change vs Chemical Change

Image of physical change vs chemical change

Question 17:

Write word equations for two chemical reactions with the help of materials given in the box.

Air, copper sulphate, iron, vinegar, iron oxide, carbon dioxide, iron sulphate, copper, lime water, water

Answer:

Question 18:

Explain the following:

  1. Lime water turns milky on passing carbon dioxide gas into it.

  2. Bubbles are produced when acetic acid is added to a solution of sodium hydrogencarbonate.

Answer:

  1. When carbon dioxide reacts with lime water , then calcium carbonate and water is formed.

    Calcium carbonate being insoluble white powder gives milky appearance to water.

  2. When baking soda is added to acetic acid then carbon dioxide gas is formed which causes appearance of bubbles.