Secondary Standard Substance : The substance which can not kept on open place and they easily react with the components of air (O2, CO2 etc.), react with balance when they are weighting are called Secondary Standard Substance. e.g. HCL, H2SO4, NaOH, KOH, KMnO4, etc. are the Secondary Standard Substance.
A secondary standard is a standard that is arranged in the laboratory for a definite analysis. It generally does not stay constant and its concentration will usually reduce over time so high accuracy measurements made during preparation will not hold up. It is generally standardized against a primary standard.
Example: The foundation Sodium hydroxide (NaOH) is an example of a secondary standard.
Commercially available NaOH contains impurities of Sodium chloride (NaCl), Sodium carbonate (Na2CO3), and Sodium sulfate (Na2SO4), and eagerly absorbs water (H2O) from the atmosphere. To determine the concentration of NaOH in a solution, it is titrated against a primary standard weak acid, such as potassium hydrogen phthalate.
Secondary Standard Solutions
Generally, substances like hydrochloric acid and sulfuric acid are not appropriate for use as primary standards because the concentration of the commercially accessible concentrated acids is not known exactly.
However, you can arrange a weaken solution of these acids with an estimated concentration, and then resolve the concentration correctly by titration with a primary standard solution of a base such as sodium carbonate (Na2CO3). Because the correct absorption of acid has been consequent by means of a primary standard, the acid is referred to as a secondary standard.
However, you can arrange a sodium hydroxide (NaOH) solution with an estimated concentration by weighing out some NaOH pellets and dissolving them in distilled water in a volumetric flask. This solution can then be titrated with an acidic primary standard solution, such as potassium hydrogen phthalate, KH(C8H4O4), in order to determine the concentration of the basic solution further correctly.
Because the accurate concentration of the foundation has been derived using a primary standard, the base is referred to as a secondary standard.
Secondary standard solutions are solutions made specifically for certain analysis.
- Purity: Secondary standard solutions are not very pure.
- Reactivity: Secondary standards are reactive than primary standards.
- Water Absorption: Secondary standards are somewhat hygroscopic.
- Application: Secondary standard solutions are used for specific analytical experiments.
For chemical composition –
- elements in iron, steels, and other metal alloys,
- sulfur in fossil fuels,
- polychlorinated biphenyls (PCBs) in oils,
- elements in foods and beverages (e.g. milk powder, wheat flour).
For physical properties –
- strength and melt flow of polyethylene pipe,
- the electrical resistivity of silicon.