Qualitative Analysis of Salt

Qualitative analysis of an unknown salt consists of the detection and identification of the constituent ions. The inorganic salts on dissolving in water dissociate completely into positively and negatively charged ions.

An positively charged ion is called cation or a basic radical and the negatively charged ion is called an anion or an acid radical. A number of tests are carried out to identify the ions.

Qualitative analysis is done by carrying out two kinds of tests:

• Dry tests
• Wet tests

The dry tests are performed on solid inorganic substances. These tests should be performed before proceeding with wet tests.

Dry Tests

During a dry test, you should note

• (i) physical examination of salt such as colour, smell and density of the salt gives valuable clues regarding the nature of some of the basic and acid radicals
• (ii) action of heat on dry salt

Wet Tests

The wet tests are carried out in solution. In a wet test, you should note

• (i) the colour and smell of the gas evolved
• (ii) formation or disappearance of a colour of solution
• (iii) formation or disappearance of a precipitate

To detect the anion and cation in a salt, certain chemicals are used. These chemicals are called Reagents. When reagents react with salts, new compounds are formed with some observable properties such as colour, smell and characteristic appearance of precipitate.

Before carrying out systematic analysis, it is necessary to know few important laboratory techniques.