Gravimetric factor

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The gravimetric factor is the number by which the weight of a gravimetric determination has to be multiplied in order to obtain the mass of the analyte it contains .

definition

The gravimetric factor is calculated as the quotient of the molar mass of the analyte and the weighing form . So it says how high the mass fraction of the substance you are looking for is in the weighing form.

Empirical factor

Despite the exact definition on the basis of precisely known data, namely the molar masses of the ions involved , incorrect results are obtained with some gravimetric methods if one multiplies with the calculated factor. Thus, in the determination of lead as lead (II) chromate always a reproducible small amount of chromate ions coprecipitated. This is balanced out by using the "empirical factor" 0.6401, while the "arithmetical factor" 0.6411 results in a lead content that is incorrectly too high.

Practical consideration

The gravimetric factor always has a value between zero and one. In practice, a small value is advantageous, since the same absolute error in weighing then leads to a smaller relative error in the entire analysis than with a value close to one (see " Measurement error "). Since the mass of the analyte cannot be influenced, a small gravimetric factor is achieved by choosing a counterion or complexing agent with a high molar mass. The precipitation of nickel with diacetyldioxime can serve as an example , for which the gravimetric factor is 0.203 (two molecules of diacetyldioxime per molecule of nickel).

literature

  1. F. Bracher, F. Dombeck, C. Ettmayr, H.-J. Krauss: workbook quantitative inorganic analysis. Govi-Verlag, Eschborn 2003