Purity of Substance
Purity of Substance
Definition and Importance
- Purity refers to how free a substance is from other substances.
- In chemical terms, a pure substance contains only one type of element or compound.
- The purity of substances is important in a variety of fields such as medicine, manufacturing, and research.
Identifying Pure Substances
- A pure substance will always have definite physical and chemical properties such as boiling point, melting point, density, and solubility.
- Pure substances always melt and boil at specific temperatures because their microscopic structure is uniform.
- A pure substance's boiling point or melting point can be used to identify the substance, as these properties are unique to each substance.
Impure Substances
- Mixtures are considered impure substances as they contain two or more different substances not chemically combined together.
- For instance, air is a mixture of mainly nitrogen and oxygen gases.
- Impure substances have varying boiling points and melting points because their microscopic structure differs.
- As a result, they often melt or boil over a range of temperatures instead of a specific temperature.
Methods of Purity Check
- Melting Point Testing: The melting point of a substance is compared against its known standard value. The closer the test value is to the standard value, the purer the substance is likely to be.
- Boiling Point Testing: Similar to the melting point test, the boiling point of a substance can also be used to check its purity by comparing it against known values.
- Chromatography, in its various forms (paper, thin layer, gas etc.), is used to separate and identify different substances in a mixture. The distances moved by different substances up a chromatography paper or the time taken for substances to appear in a gas chromatograph can help identify and determine the purity of substances.
Purity in Industry
- In pharmaceuticals, it is vital that each drug contains the exact amount of pure substance stated to ensure it's safe and effective.
- In food production, the purity of substances such as additives and preservatives is significant for health and safety.