Gravimetry

Gravimetric analysis is the process of converting an element into a definitive compound, isolating this compound from other constituents in a sample and then weighing the compound (Box 20.1). The weight of the element can then be calculated from the formula of the compound and the relative atomic masses of the elements involved. You need to be able to weigh accurately, by difference, a substance to four decimal places.

*Note: The essential component of gravimetric analysis is the transformation of the element of interest into a pure stable solid compound, suitable for weighing.

The most common approach for isolating the element is by precipitation from a solution where it is present in ionic form. Ideally, the constituent under investigation is precipitated out of solution as a waterinsoluble compound, so that no losses occur when the precipitate is separated by filtration, washed free of soluble impurities and then weighed.