Gravimetric Analysis

When adding to the weigh boat remove it from the balance. This prevents spillage onto the balance which will affect your weighing accuracy

• Mass of empty weigh boat - now add approximate mass of substance you need • Mass of weighing boat and substance (A) - tip substance into where you want it • Reweighing empty boat plus residue (B) • Mass of substance used A-B

• Put a weigh boat on balance and zero - now add a,out of substance required • Mass of weigh boat and substance X -tip substance into where you want it • Reweigh empty boat and residue Y • Mass of substance used X-Y

Get an accurate value close to the required amount but ensure you record the the actual mass given on the balance

Heating to constant mass ensures that all the water has been removed

The sample must be cooled in a desiccator so no moisture can be reabsorbed as the silica (chemical in the base) in the desiccator keeps the atmosphere dry

repeating the steps of heating, cooling and weighing until no further changes in mass are observed

Gravimetric analysis is used to determine the mass of an element or compound in a substance

The substance is converted into another substance of known chemical composition, which can readily be isolated or purified, this conversion can occur either through precipitation or volatilisation

In precipitation conversion the substance undergoes a precipitation reaction. The precipitate is separated from the filtrate and the filtrate tested to ensure the reaction has gone to completion. The precipitate is washed, dried to constant mass and then weighed.

In volatilisation conversion the substance is heated and any volatile products (often water) are evaporated. The substance is heated to constant mass and the final mass recorded.