Gravimetric Analysis Flashcards
what is gravimetric analysis used for
to determine the mass of an element or compound in a substance
what are the two major types of gravimetric analysis
volatilisation
precipitation
description of volatilisation
the substance is heated and any volatile products are evaporated
the substance is heated to constant mass and the final mass recorded
what is heating to a constant mass
a substance is heated, cooled then weighed
these steps are repeated until no further changes in mass are observed
what does heating to a constant mass ensure
the reaction has gone to completion
why is a crucible originally heated
go drive off any substances adhering to the surfaces of the lid
what is the purpose of the dessicator?
provides a dry atmosphere and allows the cruicible and lid to cool without absorbing moisture
why does the substance need to cool in heating to a constant mass
their measured mass will be less than their true mass
describe precipitation
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 then weighed
in precipitation, what size should the particles be and why
large
they are more easily filtered than small
small could clog the filter or pass through
large have smaller surface area so can be washed free of impurities easier
how to promote the formation of large particles for precipitation
acidification of mixture
slow addition of substance
vigorous stirring
vigorous heating
