Q.Explain the cleansing action of soap.

Colloids have important medicinal uses; colloidal antimony specifically is used against Kala-azar.

Many metals and metal compounds are used therapeutically in the colloidal state because the very small particle size gives them better absorption and biological activity. Colloidal antimony (and antimonial compounds) has historically been used in the treatment of Kala-azar (visceral leishmaniasis), a parasitic dis …

Gelatine is used as a protective colloid: it forms a protective envelope around lyophobic sol particles so electrolytes can no longer coagulate them.

Lyophobic sols (like As2S3, Au sol, or Fe(OH)3 sol) are unstable — they are easily coagulated (precipitated) by adding even small amounts of electrolyte. Lyophilic colloids (which have a strong affinity for the dispersion medium, usually water) can be added to a lyophobic sol to coat each particle with a protective layer; the electrolyte can then no longer approach and destabilise the sol particle directly. This protective ability is measured by the 'gold number' — the minimum mass (in mg) of a protective colloid needed to prevent the coagulation of 10 mL of a standard gold sol on adding 1 mL of 10% NaCl solution. A smaller gold number means a better protective colloid; gelatine has one of the smallest gold …

Gold number is defined as the minimum weight (in mg) of a protective (lyophilic) colloid that must be added to 10 mL of a standard gold sol just to prevent its coagulation when 1 mL of 10% NaCl solution is added; smaller gold number = greater protective power.

Lyophilic colloids (e.g. gelatin, starch, gum) can be added in small amounts to a lyophobic sol (like gold sol) to form a protective layer around the sol particles, preventing them from coagulating when an electrolyte is added. The gold number quantifies exactly this protective ability of a given lyophilic …