JEE Main 2023 · 24 January · morning · Single correct · +4 / −1
Statement I : For colloidal particles, the values of colligative properties are of small order as compared to values shown by true solutions at same concentration.
Statement II : For colloidal particles, the potential difference between the fixed layer and the diffused layer of same charges is called the electrokinetic potential or zeta potential.
In the light of the above statements, choose the correct answer from the options given below
- (a) Both Statement I and Statement II are false
- (b) Statement I is true and Statement II is false
- (c) Both Statement I and Statement II are true
- (d) Statement I is false but Statement II is true
Answer and solution
Answer (b) Statement I is true and Statement II is false
Solution
Chemistry ma’am · 4 steps
Statement I is right, but Statement II hides one wrong word: the diffused layer carries the opposite charge.
- Statement I. Colligative properties depend on the number of particles, not on their size. A colloidal particle is a huge aggregate of many molecules, so the same mass gives far fewer particles than a true solution. The colligative effect is therefore much smaller, and Statement I is true.
- The double layer. A colloidal particle adsorbs ions of one kind and gets a charge. This is the fixed layer. It attracts ions of the opposite charge from the medium, and these form the diffused layer around it.
- Statement II. The zeta (electrokinetic) potential is the potential difference between the fixed layer and the diffused layer of opposite charges. Statement II says "same charges", so it is false.
- So. Statement I is true and Statement II is false, which is option (b).
The idea to keep. In statement questions, read every word of a definition. The Helmholtz double layer always has opposite charges, which is why there is a potential difference across it at all.
Answer from the NTA final answer key. Solution by PrepWiser.