The gold number range of some of the lyophilic colloids is given below :
A : 0.005 - 0.01, B : 0.15 - 0.25, C : 0.04 - 1.0 and D : 15 - 25.
Which among these can be used as a better protective colloid ?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A
A lyophilic colloid added to a lyophobic sol forms a layer around the sol particles and protects them from coagulation by electrolytes; it is then called a protective colloid. Its protecting power is measured by the gold number: the number of milligrams of the protective colloid that just prevents the coagulation of 10 mL of a red gold sol when 1 mL of 10% sodium chloride solution is added to it.
The smaller the gold number, the less of the colloid is needed, so the greater is its protective power. Colloid A has the smallest gold number (0.005–0.01), so A is the best protective colloid.
Shortcut: Protective power is inversely related to gold number; pick the smallest range.
Note: The question is from beyond the NCERT textbook.