Q. Which of the following is/are the example/examples of chemical change?

  1. Crystallization of sodium chloride
  2. Melting of ice
  3. Souring of milk

Select the correct answer using the code given below.

  • 1 and 2 only
  • 3 only
  • 1, 2 and 3
  • None

Answer: (b) 3 only

Chemical Change
  • When one chemical substance is transformed into one or more different substances, it is called a chemical change. The most common example is when iron transforms into rust.
  • Crystallization of sodium chloride
    • When the solubility limit of NaCl exceeds, the crystallization of NaCl takes place.
    • It is a physical change since sodium chloride does not transform into some other chemical element after crystallization.
  • Melting of ice
    • Ice is the solid form that liquid water takes when it is cooled below 0 degrees celsius.
    • When the temperature rises, solid ice changes into liquid water.
    • It is not a chemical change since the composition of water molecules stays the same before and after melting.
  • Souring of milk
    • Lactic acid bacteria ferment lactose at room temperature and turn it into lactic acid.
    • As a re­sult, the acid­i­ty of the milk in­creas­es, which in its turn caus­es the pro­tein to fold and liq­uid to sep­a­rate into whey and a vis­cous mass.
    • The soured milk has new elements and it cannot be reversed. Hence, it is a chemical change.
Chemical Change