The charges on the colloidal CdS sol and $\mathrm{TiO}_{2}$ sol are, respectively:

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Surface Chemistry

The charges on the colloidal CdS sol and

TiO_{2}

sol are, respectively:

(A)Positive and negative
(B)Positive and positive
(C)Negative and positive✓ Correct
(D)Negative and negative

Answer: (C)

Solution

A colloidal particle takes its charge from the ion it adsorbs preferentially from the dispersion medium. Cadmium sulphide sol is prepared by passing hydrogen sulphide into a cadmium salt solution, so sulphide ions are in excess and are adsorbed on the particle surface, leaving the sol negatively charged. Titanium dioxide is a hydrous metal oxide whose surface takes up hydrogen ions from water, leaving that sol positively charged. The cadmium sulphide sol is negative and the titanium dioxide sol is positive.

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Single correct option

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