Here’s a explanation of the role of drying and ignition in gravimetric analysis:
1. Drying
- After filtration, the precipitate still contains water and impurities.
- Drying removes this moisture by heating it at a moderate temperature (usually in an oven).
- The goal is to make the precipitate completely dry so that its weight is accurate and constant.
Why it’s important:
- Water left in the solid would make it heavier and give false results.
- Drying ensures that the mass measured is only of the compound, not of water.
2. Ignition
- Sometimes drying is not enough. The precipitate is then heated strongly (ignited) in a furnace.
- Ignition helps to:
- Remove all moisture and volatile materials.
- Convert the precipitate into a stable, known compound that won’t change on standing (for example, hydroxides to oxides).
Example:
- Calcium oxalate (CaC₂O₄) is ignited to form calcium oxide (CaO) before weighing.
In short:
- Drying removes water.
- Ignition removes all volatile substances and forms a stable compound for accurate weighing.
Purpose: To make sure the final solid is pure, stable, and has a constant weight for precise results.