Washing, Drying, and Ignition of Precipitates

Following filtration, the precipitate is washed to remove coprecipitated impurities and any remaining mother liquor.

Colloidal precipitates, such as silver chloride, are washed with an electrolyte to prevent peptization.

In the case of slightly soluble precipitates, such as lead sulfate, the wash solution contains a common ion to reduce solubility.

Similarly, wash solutions may be basic or acidic to prevent the hydrolysis of salts of weak acids and weak bases, respectively.

Following washing, the precipitate is dried to remove adsorbed water and volatile organic solvents.

In some cases, ignition is required to convert the precipitate to a suitable weighing form.

Finally, the precipitate is cooled in a desiccator and weighed.