NCERT Class VII Science Solutions: Chapter 6-Physical and Chemical Changes Part 3 (For CBSE, ICSE, IAS, NET, NRA 2023)

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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)
Column IColumn II
  1. 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)
Column IColumn II
  1. Large crystals
iv Sugar candy (Mishri)
  1. Depositing a layer of zinc on iron
vi Galvanisation
  1. Souring of milk
v Chemical change
  1. Carbon dioxide
i Turns lime water milky
  1. Iron oxide
iii Rust
  1. 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

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.

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