Question

Choose the incorrect option among the following:

• A. Lyophilic sols are reversible sols
• B. Lyophobic sols are irreversible sols
• C. Lyophobic sols need stabilising agents for their preservation
• D. Lyophobic colloids are directly formed by mixing substances like gum, gelatine, starch, rubber, etc., with a suitable liquid (the dispersion medium)

Answer 1

The correct option is D Lyophobic colloids are directly formed by mixing substances like gum, gelatine, starch, rubber, etc., with a suitable liquid (the dispersion medium)

(a)
An important characteristic of lyophilic sols is that if the dispersion medium is separated from the dispersed phase (say by evaporation), the sol can be reconstituted by simply remixing with the dispersion medium. That is why these sols are also called reversible sols.
(b) These sols are readily precipitated (or coagulated) on the addition of small amounts of electrolytes, by heating or by shaking and hence, are not stable. Further, once precipitated, they do not give back the colloidal sol by simple addition of the dispersion medium. Hence, these sols are also called irreversible sols.
(c) Lyophobic sols need stabilising agents for their preservation, since they are not stable.
(d) Lyophobic colloids are not prepared when simply mixed with the dispersion medium, they do not form the colloidal sol. Their colloidal sols can be prepared only by special methods.