Q: Which of the following is/are the example/examples of chemical change?
a) Crystallization of sodium chloride
b) Melting of ice
c) Souring of milk
The correct answer is 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. Hence, Statement 1 is not correct.
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.
- Melting of Ice is not a chemical change since the composition of water molecules stays the same before and after melting. Hence, Statement 2 is not correct.
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. Therefore, souring of milk is a chemical change. Hence, Statement 3 is correct.
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