Question

Milk turns sour. is this a chemical or physical change

Answer 1

Physical change:

• In a physical change, the molecules of a substance are rearranged but the composition of the substance remains constant.
• Physical change is reversible which means that the original can be recovered.

Chemical change:

• In a chemical change, the molecular composition of a substance is completely changed and it gives rise to a new substance.
• Chemical changes are irreversible which means that the original cannot be recovered.

Milk turns sour:

• When milk turns sour, the bacteria are converting the lactose sugars in milk into energy, with lactic acid as a byproduct.
• The souring of milk results in the production of sour-tasting lactic acid.
• In this chemical process, new substances that are lactic acid have been formed.

Therefore, Milk turns sour is a chemical change.