The solution with known concentration is called standard solution. It is of two types.
- Primary standard solution: The standard solution which is prepared by direct weightage of solute in the calculated amount of solvent is called primary standard solution.
Criteria for a solution to be primary standard solution:
- It should be available in pure and dry state.
- Its composition should not be changed on storage. i.e., It should not be toxic, volatile, hygroscopic and deliquescent.
- It should be highly soluble in water without any change in its composition.
- It should have higher molecular and equivalent weight. S
Some of the examples of primary standard solution are: Sodium carbonate (Na2CO3), Potassium dichromate (K2Cr2O7), oxalic acid (COOH)2.2H2O, Mohr’s salt etc.
- Secondary standard solution: The standard solution whose concentration is measured with the help of primary standard solution is called secondary standard solution. Example: NaOH, HCL, H2SO4 etc.