Qualitative techniques for inorganic analysis

Qualitative techniques are used to identify cations and anions in aqueous solution by simple reactions, mostly involving the production of a precipitate, evolution of gas or a visual colour change. It is important to make observations accurately and to interpret them in a step-wise manner.

The following basic equipment is required to carry out qualitative analysis:

• Test tubes - in which the reactions are performed.
• Cork or rubber stoppers - for the protection of the contents of test tubes from contamination and for safe storage.
• Test tube rack - this allows test tubes to be stored upright when not in use.
• Test tube holder - this allows individual test tubes to be heated safely.
• A glass rod - this has several functions including the stirring, transfer of solutions, and the break-up of precipitates.
• Watch-glasses these have several functions including the covering of beakers to prevent contamination and as a receptacle for solutions.
• A wash bottle containing distilled water.
• Spatula - for transferring small quantities of solids.
• Pasteur pipettes - for transferring liquids.
• Micro-Bunsen burner - for heating solutions to boiling and for evaporating solutions.
• Evaporation crucible - this is used as a container for solutions when complete evaporation of liquid is required, leaving a solid product.
• Crucible tongs - for removing the crucible from the heat source.
• Centrifuge - for separating precipitates from solution.
• Heated water bath.