JEE Main 2021 · 16 March · evening · Single correct · +4 / −1
The INCORRECT statements below regarding colloidal solutions is :
- (a) The flocculating power of Al³⁺ is more than that of Na⁺.
- (b) A colloidal solutions shows Brownian motion of colloidal particles.
- (c) An ordinary filter paper can stop the flow of colloidal particles.
- (d) A colloidal solutions shows colligative properties.
Answer and solution
Answer (c) An ordinary filter paper can stop the flow of colloidal particles.
Solution
Chemistry ma’am · 2 steps
Colloidal particles are small enough to pass through filter paper; only an ultrafilter holds them back.
- Size decides it. Colloidal particles are about 1 to 1000 nm across. The pores of ordinary filter paper are larger than this, so the particles pass straight through.
Statement True or false Reason (a) Al³⁺ flocculates better than Na⁺ True Hardy–Schulze rule: higher charge on the coagulating ion gives greater flocculating power, so Al³⁺ > Na⁺ for a negative sol (b) Brownian motion True Solvent molecules strike the particles unequally from all sides, so the particles move in a zig-zag path (c) Filter paper stops colloidal particles False The particles are smaller than the pores. Only ultrafilter paper (filter paper soaked in collodion) can stop them (d) Colligative properties True They are shown, but the values are very small because colloidal particles are large and few in number - So. The only incorrect statement is (c). That is why ultrafiltration, not ordinary filtration, is used to separate colloidal particles.
The idea to keep. Ordinary filter paper stops suspensions but not colloids; ultrafilters stop colloids but not true solutions. Colloids still show colligative properties, only in very small values.
Answer from the NTA final answer key. Solution by PrepWiser.