Question

Explain the following terms:
Hardy-Schulze’s rule

Answer 1

Hint: Hardy-schulze rule gives us an idea of the amount of electrolyte required to coagulate a colloidal solution. This rule was an observation of Hardy and Schulze.

Complete step by step answer:
> Hardy Schulze rule states that the amount of electrolyte required for the coagulation of a definite amount of a colloidal solution is dependent on the valency of the coagulating ion. Coagulating ion is the ion which has the charge opposite to the charge of the colloidal particles). Coagulation is the process of coming together of colloidal particles which results into the formation of larger particles which eventually settle down as a precipitate or float on the surface. Coagulation is generally brought about by the addition of electrolytes. When an electrolyte is added to a colloid, the particles of the colloid attract the ions which are oppositely charged to them and thus get neutralized. The neutralized particles accumulate to form larger particles which eventually settle down. The ions of the electrolyte which cause the colloid to coagulate are called flocculating or coagulating ions. Hardy and Schulze observed that greater the valency of the flocculating ion or coagulating ion, the greater is its power to coagulate.
> Also, the minimum amount of an electrolyte that must be added to one litre of a colloidal solution so as to bring about complete coagulation or flocculation is called the coagulation or flocculation value of the electrolyte. Thus, smaller is the flocculation value of an electrolyte; greater is its coagulating or precipitating power.
Example: \[P{O_4}^{ - 3}\] coagulates a positive sol more effectively than \[C{l^ - }\] as the valency of (-3) is numerically greater than that of (-1).
Similarly, \[A{l^{ + 3}}\] ions coagulate a negatively charged sol more effectively than \[N{a^ + }\] ions.

Note:
Make sure to remember that the coagulating value of a negative sol is determined by the valency of the positive ion of the electrolyte added, and vice versa.