Question

Gold number is the measure of protective power of a lyophobic colloid.
(A) True
(B) False

Answer 1

The Lyophobic colloids have the power to prevent the precipitation of lyophilic colloids by the addition of an electrolyte to the lyophobic colloids and this protective character can be measured quantitatively.

Complete step by step answer:
-First of all we will see what lyophobic and lyophilic colloids are.
Colloids are basically phase separated mixtures where one substance of dispersed insoluble or soluble is suspended throughout another substance which acts as dispersion medium. So, colloids consist of a dispersion medium and a dispersed phase.
On the basis of nature of interaction between dispersed phase and dispersion medium colloids are classified into:
(1)Hydrophilic colloids: They are also known as water loving colloids because colloidal particles are attracted to water and are reversible sols. For example: pectin, agar, gelatine, etc.
(2)Hydrophobic colloids: They are also known as water hating colloids because the colloidal particles are repelled by water and are irreversible sols. For example: Gold sols and clay particles.
-We will now talk about what a gold number is.
The power of hydrophilic colloids to prevent the hydrophobic colloids from precipitating by the addition of an electrolyte will depend on the nature of the substance. This protective character of hydrophilic colloids is expressed quantitatively as gold number.
Hence gold number is basically defined as: the amount of protective colloid (hydrophilic colloid) in milligrams (mg) which should be added to 10 ml (cc) of some given sol (hydrophobic colloid) so as to just prevent its precipitation by addition of 1 ml (cc) of 10 % NaCl solution.
-Gold number is inversely proportional to the protective power of the colloid. This means that more is the gold number, lesser is the protective power of the lyophilic colloid and hence more amount of lyophilic colloid will be required to prevent precipitation of the lyophobic colloids.
Gold number α $\frac{1}{{P.P.}}$
Where, P.P. is the protecting power of the lyophilic colloids.
Hence the statement given in the question is false because gold number is the measure of protective power of lyophilic colloids, not the lyophobic colloids.

So, the correct option is (B) False.

Note: When the colour of the gold sol changes from red to blue/purple with increasing particle size, it is an indication of coagulation. Also the weight or amount of the lyophilic colloid we take to prevent coagulation is always taken in milligrams (mg).