Factor (chemistry)

The term factor has several meanings in chemistry. Measured values ​​found in dimensional analysis or gravimetry are multiplied by such a factor in order to calculate the amounts of substance on which they are based. In dimensional analysis, the factor of a titration solution is determined experimentally with the help of a basic titer substance . In gravimetry, the factor results from the stoichiometry .

Factor of bespoke solutions

In the volumetrics ( volumetric analysis ) dimensionless number used (usually with three or four decimal places) with the milliliter consumption are multiplied a titration solution (standard solution) of a nominal concentration must to determine the milliliters consumption of an exactly normal titration. Such - mostly minor - deviations from the nominal concentration (e.g. 0.1 N hydrochloric acid) can result

• Weighing or dimensional errors when preparing the titration solution or
• slight decomposition if the titration solution is stored for a long time
• if the solution is used several times due to evaporation of the solvent

be justified. Therefore the factor determination should be repeated at regular intervals. The frequency depends on several factors, such as the stability of the reagent , accuracy requirements, storage time, etc. In order to determine the exact substance concentration , the present concentration of the solution is determined by means of a titration with a primary titer substance . The quotient of the found ( ) and nominal ( ) concentration is the factor (also titer ) of the standard solution. ${\displaystyle {c_{\text{ist}}}}$ ${\displaystyle {c_{\text{soll}}}}$ ${\displaystyle {t}}$

${\displaystyle t={\frac {c_{\text{ist}}}{c_{\text{soll}}}}}$

example

If a real concentration of 0.510 mol / l is determined for a nominally 0.500 molar hydrochloric acid solution after determining the content, it has a factor of 1.020. This factor must be offset for later titrimetric determinations.

Gravimetric factor

Dimensionless number used in gravimetric methods (usually with three or four decimal places), with which the weight of a precisely defined substance must be multiplied in order to directly determine the amount of a sought

• Elements ,
• Acid residue or one
• connection

to be able to calculate in a weighed analysis sample. These factors are the quotient of the molar mass of the element or compound sought and that of the balanced compound.

example

When determining barium, it is precipitated as sulphate and balanced. Then 1 mg of barium sulfate (molar mass 233.39 g / mol) corresponds to 0.5884 mg barium (molar mass 137.327 g / mol). The factor is then 0.5884.

These factors are listed in tables such as the Küster-Thiel calculation tables for chemical analysis or the CRC Handbook of Chemistry and Physics .

Individual evidence

1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 2: Cm-G. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1981, ISBN 3-440-04512-9 , p. 1234.
2. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 979-980.
3. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 389.