Which of the following is/are the example/examples of chemical change?
- Crystallization of sodium chloride
- Melting of ice
- Souring of milk
Select the correct answer using the code given below.
[UPSC Civil Services Exam – 2014 Prelims]
(a) 1 and 2 only
(b) 3 only
(c) 1, 2 and 3
- Crystallization of sodium chloride – It is a physical change since sodium chloride does not transform into some other chemical element after crystallization.
- Melting of ice – 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.