Question

Which one of the following is a primary standard?

• A. Oxalic acid
• B. Sodium thiosulphate
• C. Sodium hydroxide
• D. Potassium dichromate

Answer 1

Answer: (D)

Potassium dichromate

The primary standard is a compound of sufficient purity from which standard solutions of known normalities can be prepared by direct weighing of it and diluting to a defined volume of solution.

Potassium Dichromate$\left(K_{2}C{r}_2{O}_7\right)$ is suitable to be used as a primary standard. It cannot be obtained in very pure form. It readily reacts with any traces of organic material or any other reducing substance in water.