Gold number of a protective colloid is the minimum weight of it in  milligrams which must be added to 10 mL of a substance (red gold sol)  so that no coagulation of the gold sol takes place when 1 mL of 10%  sodium chloride solution is rapidly added to it. or Weight of the dried protective agent in milligrams, which, when added  to 10 mL of a standard gold sol (0.0053 to 0.0058%), is just sufficient to  prevent a color change from red to blue on the addition of 1 mL of 10%  sodium chloride solution, is equal to the gold number of protective  colloid.  Protective power ∝ 1/Gold number Note: Gold number is a practical value, it cannot be obtained  theoretically.

Adsorption is a surface phenomenon in which molecules of a substance (called the adsorbate ) accumulate on the surface of another substance (called the adsorbent ). It occurs due to the presence of unbalanced forces at the surface of solids or liquids, which attract the adsorbate particles. Adsorption can be of two types — physical adsorption (physisorption) , involving weak van der Waals forces, and chemical adsorption (chemisorption) , involving strong chemical bonds. It plays an important role in many processes such as catalysis, purification of gases, and water treatment. Quiz Revision Notes Downloads Quiz Revision Notes Downloads ...