Compare and evaluate primary and secondary standards
Why are they used in analysis?
A primary standard is a highly purified compound which acts as a reference in all titrimetric volumetric analysis. A secondary standard is titrants that is standardized against a primary standard or another standard solution and are used for certain types of analysis. A primary standard is a reagent that is extremely pure, stable, it’s not a hydrate/has no water of hydration and has high molecular weight. A primary standard is used to calibrate other standards referred to as working standards. Examples of primary standards for titration of acids are:
Sodium carbonate, tris-hydroxylmethyl amino methane.
Examples of primary standards for titration of bases are:
Potassium hydrogen phthalate and potassium hydrogen iodate
Examples of primary standards for redox titrations are:
Potassium dichromate (K2Cr2O7 )and sodium oxalate (Na2C2O4)
A secondary standard is a standard that is prepared in the laboratory for specific analysis. It is usually standardized against a primary standard. Standard has the following uses in a chemical analysis;
1. It provides a reference which we can use to determine unknown concentration 2. To standardize volumetric solutions
3. Preparation of secondary standard
4. To calibrate an instrument.
A secondary standard is a solution that is not stable in its own form and must first be standardized before being used, a good example is NaOH. Some materials are difficult to measure directly, for example, NaOH a very common base is an example , it is very hygroscopic i.e. it absorbs water from the atmosphere, also means that its mass basically changes while you are measuring it (actually it is deliquescent; it absorbs enough water to dissolve itself). Since it can’t be measured reliably, it can’t really be used as a primary standard but it can be titrated against a primary standard.. Differences between primary and secondary standards
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