Question

Gold numbers of some colloids are :
Gelatin : 0.005-0.01, Gum Arabic : 0.15-0.25; Oleate : 0.04-1.0; Starch : 15-25.
Which among these is a better protective colloid?

Answer 1

Hint: We know that the gold number is the largest number of milligram of protective colloid. It fails to prevent the colour change from red to blue when 10 ml of a special standard hydro gold sol is added on 1 ml of 10% sodium chloride solution.

Complete answer:
Colloids which have lesser gold number have better protective colloids. From the above options we can observe that the gold number of Gelatin is lowest regarding other options.

Hence, among them Gelatin is a better protective colloid.

Additional Information:
On adding lyophilic colloid to a lyophobic colloid, the latter is rendered less sensitive to the precipitating action of an electrolyte. Lyophilic colloids protect a lyophobic colloid from precipitation by the action of electrolytes. The lyophilic particles form a coating around lyophobic particles when applied to the lyophobic sol and thus the latter is protected from electrolytes. The use of Lyophilic colloids to this purpose are known as protective colloids. The protective action of a lyophilic sol depends on various factors like sol dispersity, the molar mass of the lyophilic sol, the pH of the solution in which the experiment is performed.

Note:
A student can confuse between lyophilic colloid and lyophobic colloid. Lyophilic colloids are solvent-loving colloids; they are also called gels. Lyophobic colloids are solvent-fearing; they are also called sols.