Give an example of a chemical reaction for each of the following situations: A change in colour is observed. A gas is evolved. Sound is produced. Formation of precipitate. Change of state from liquid to gas. Change of state from gas to liquid

cbse
cbse-class-7-science
chemical-changes
physcial-and

#1

Give an example of a chemical reaction for each of the following situations:

  1. A change in colour is observed.
  2. A gas is evolved.
  3. Sound is produced.
  4. Formation of precipitate.
  5. Change of state from liquid to gas.
  6. Change of state from gas to liquid.

Answer:

  1. Reaction between copper sulphate soludon and zinc metal. The blue colour of the copper sulphate solution fades away and a red brown metallic copper is formed,
  2. Reaction between baking soda and vinegar. Baking soda on reaction with vinegar produces carbon dioxide.
  3. Burning of crackers.
  4. Reaction of silver nitrate and potassium chloride. A precipitate of silver chloride is formed.
  5. When water is heated above boiling point, it converts into vapours.
  6. Water droplets appear on the outside of a bottle containing cold water.