Drying to Constant Mass

When a solid is obtained, it may contain trace amounts of water or volatile impurites. To ensure that the substance does not contain any water or other volatile impurities, the substance is dried to constant mass. 

1. Isolate the solid from all other substances. Filtration is the most common technique to isolate the solid.

2. Determine the mass of the sample.

3. Allow the sample to dry at room temperature over night or place the sample into a drying oven for a set period of time. This allows the water and other volatile impurities to evaporate.

4. Determine the mass of the sample again If the mass does not change, the sample has been dried completely and the sample does not contain any water or other volatile impurities. If the mass changes, continue drying.

5. Continue drying and massing the sample until two consective masses are obtained.

Drying ovens subject the solid to low temperatures. If higher temperatures are required or does not cause the sample to decompose, the sample can be heated in a crucible using a Bunsen burner.