Impurity

For a solid, an impurity often makes the melting point lower and broadens the melting range. The safest general conclusion, however, is based on the contrast between a sharp, specific temperature and a temperature range; the precise effect depends on the substances present.

One possible impurity is sulfur.

At GCSE level, the expected pattern is that an impurity usually lowers the melting temperature and widens the melting range. Instead of melting sharply, the sample begins melting at one temperature and does not finish until a higher temperature.

Removal of impurities: contaminated material may require extra cleaning or purification. This increases the use of energy, water or chemicals and may produce additional waste.