Gravimetric factor

The weight of the precipitate after filtering and drying can then be measured free of any influence from the NaCl and converted back to the weight of the analyte with the use of a gravimetric factor (see the next section) and its percent in the sample calculated. Examples are given in Section 3.6.4. 

A gravimetric factor is a number used to convert, by multiplication, the weight of one chemical to the weight of another. Such a conversion can be very useful in an analytical laboratory. For example, if a recipe for a solution of iron calls for 55 g of FeCl3 but a technician finds only iron wire on the chemical shelf, he or she would want to know how much iron metal is equivalent to 55 g of FeCl3 so that he or she could prepare the solution with the iron wire instead and have the same weight of iron in either case. In one formula unit of FeCl3, there is one atom of Fe, so the fraction of iron(III) chloride that is iron metal is calculated as follows  

The weight of iron metal that is equivalent to 55 g of iron(III) chloride can be calculated by multiplying the weight of iron(III) chloride by this fraction  

This fraction is therefore a gravimetric factor because it is used to convert the weight of FeCl3 to the weight of Fe, as shown. 

The general formula for a gravimetric factor is then as follows  

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Table 11.26 Heating Temperatures, Composition of Weighing Forms, and Gravimetric Factors...

Gravimetric factors are based on the 1993 International Atomic Weights. The factor Ag 0.7526 given in the first line of the table indicates that the weight of precipitate obtained (AgCl) is to be multiplied by 0.7526 to calculate the corresponding weight of silver. 

Element Thermal stability range, °C Final heating temperature, °C Composition of weighing form Gravimetric factors... 

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