Describe the use of “primary standards” in chemical analyses: a) first briefly d

Question

Describe the use of “primary standards” in chemical analyses: a) first briefly define the role of the standard in making the analysis quantitative; and b) list any special characteristics of primary standards or required steps in preparing it for analysis.

In the response, it may be helpful to consider one or more example: for instance, the EDTA titration of Ca2+ and Mg2+, the NaOH titration of KHP, or the S2O32– titration of IO3–. The question is not asking you to list procedures specific to any one of these, but instead general principles common to them.

Explanation / Answer

A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are used to calibrate other standards referred to as working standards

Here, a primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained

Answer a ) Role of standard in making the analysis quantitative

A standard provides a reference that can be used to determine unknown concentrations or to calibrate analytical instruments.

A solution of acid can be standardized by titrating it against a solution of alkali of known concentration. Once this has been calculated, it can in turn be used as a standard solution to find the concentration of a solution of alkali.

Standard solutions are also commonly used to determine the concentration of an analyte species

. By comparing the absorbance of the sample solution at a specific wavelength to a series of standard solutions at differing known concentrations of the analyte species, the concentration of the sample solution can be found via Beer's Law.

Answer b)

Features of a primary standard include:

Some examples of primary standards according to the European Pharmacopoeia 5, ch. 4.2:

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