Differences Between Primary and Secondary standards
Primary and Secondary standards
Differences Between Primary and Secondary standards.
Primary Standards
The substance of high purity used in the preparation of standard solution is called as a primary standard.Following requirements
- It must be easy to obtain, to purity, to dry, and stable under storage condition.
- It must be readily soluble in water.
- Impurities should not exceed 0.01-0.02 (99.98-99.99%pure).
- It should have high equivalent weight so that weighing error may be negligible.
- It should have a high equivalent weight.
- Titration error should be negligible.
- Uses simple indicators to determine the endpoint.
- They are analytical grade reagents.
1. Acid-base titration
Sodium carbonate (borax: primary standard).2. Oxidation-reduction
Potassium dichromate, Pot. bromate, Pot. iodate.3. Reduction
Oxalic acid, Sodium oxalate.4.Precipitation
Silver nitrate (KCl, NaCl primary standard).5.Complexometric
ZnCl, calcium chloride.Secondary Standards
A substance that is not a primary standard in nature is called a secondary standard.Examples are
1.Alkali solution (NaOH, KOH)
2.Inorganic acid(H2SO4)
3.Deliquescent substance liquid.
Secondary standard reagents require standardization by using primary standards.