JEE Main 2022 · 24 June · morning · Single correct · +4 / −1
Given below are two statements :
Statement I : Emulsions of oil in water are unstable and sometimes they separate into two layers on standing.
Statement II : For stabilisation of an emulsion, excess of electrolyte is added.
In the light of the above statements, choose the most appropriate answer from the options given below :
- (a) Both Statement I and Statement II are correct.
- (b) Both Statement I and Statement II are incorrect.
- (c) Statement I is correct but Statement II is incorrect.
- (d) Statement I is incorrect but Statement II is correct.
Answer and solution
Answer (c) Statement I is correct but Statement II is incorrect.
Solution
Chemistry ma’am · 4 steps
An emulsion is held together by an emulsifying agent; excess electrolyte does the opposite and breaks it.
- Statement I. Oil and water do not mix, so the tiny oil droplets keep meeting and merging into bigger drops. On standing, a plain oil-in-water emulsion can separate into two layers. Correct.
- How it is stabilised. A third substance called an emulsifying agent is added, such as soap, a detergent, a protein or a gum. It forms a film between each droplet and the water, so the droplets cannot merge.
- Statement II. The droplets of an emulsion carry a charge, and this charge helps keep them apart. Excess electrolyte neutralises that charge, so the droplets merge and the emulsion breaks. An electrolyte destabilises an emulsion rather than stabilising it. Incorrect.
- So. Statement I is correct and Statement II is incorrect, which is option (c).
The idea to keep. Emulsifying agents such as soaps, detergents, proteins and gums stabilise emulsions. Electrolytes, heating, freezing and centrifuging break them. Do not mix up the two lists.
Answer from the NTA final answer key. Solution by PrepWiser.