JEE Main 2021 · 25 February · evening · Single correct · +4 / −1
Which one of the following statements is FALSE for hydrophilic sols?
- (a) They do not require electrolytes for stability.
- (b) The sols cannot be easily coagulated.
- (c) These sols are reversible in nature.
- (d) Their viscosity is of the order of that of H₂O.
Answer and solution
Answer (d) Their viscosity is of the order of that of H₂O.
Solution
Chemistry ma’am · 3 steps
Lyophilic particles hold on to a thick layer of water, so think gum or starch solution, not plain water.
- What hydrophilic means. In a hydrophilic (lyophilic) sol, the dispersed particles attract water strongly. Each particle carries a thick layer of water molecules bound around it.
- Check each statement. That water layer explains every property in the options. Test each one against it.
Statement True or false Reason (a) No electrolyte needed for stability True The water layer keeps particles apart, so they do not depend on ions for stability. (b) Not easily coagulated True The water layer must be removed first. Only a large amount of electrolyte, or a liquid like alcohol, can do that. (c) Reversible True Dry out a gum or starch sol and add water again: the sol forms back on its own. (d) Viscosity close to that of H₂O False Large hydrated particles drag on the medium, so viscosity is much higher than that of water. - So. The false statement is (d). A hydrophilic sol is far more viscous than water. Viscosity close to that of water is a property of hydrophobic sols.
The idea to keep. Remember the contrast: lyophilic sols are stable, reversible and viscous. Lyophobic sols are unstable, irreversible, coagulate easily and flow like water.
Answer from the NTA final answer key. Solution by PrepWiser.