Chemical Analysis: Purity

Purity in Chemical Substances

A pure substance is composed of only one kind of particle. It could be a single element or a compound.
Substances can be considered pure if they’re chemically unaltered and are not mixed with other substances.
Changing a pure substance results in a chemical change, and the production of new substances.

The purity of a substance can be assessed by measuring its physical properties such as boiling point and melting point.
For liquids, the boiling point of a pure substance will always be sharp and precise.
The melting point of a substance is a key determinant of its purity. A pure substance will have a distinct and precise melting point.
Impure substances exhibit a melting point depression. This means that their melting points are lower than what is expected for pure substances.
Similar to the melting points, impure substances also present boiling point elevation.

The process of purification often includes techniques like filtration, crystallisation, distillation and chromatography.
Filtration is commonly used to separate mixtures of solids and liquids, while distillation separates liquids with different boiling points.
Chromatography is used to separate components of a dissolved substance.
Crystallisation is used to obtain a pure solid substances from a solution.

Purity is essential in certain industries such as the pharmaceutical industry, where the effectiveness of a drug can hinge on its purity level.
Impurities can greatly affect the properties of materials, including reactivity, hardness and colour.
Food and water purity is critical for health reasons, since impurities can lead to adverse effects.

Knowing about purity and its analysis is a crucial element in the understanding of chemical substances, their properties, and their uses.