Answer to Question #325334 in General Chemistry for Rose

Question

Why can NaOH not be used as a primary standard during titration?

Answer 1

Now sodium hydroxide cannot be used as a primary standard because of the following reasons:

1) It cannot be obtained in a state of high purity required of a primary standard.

2) NaOH is highly hygroscopic, meaning that it rapidly absorbs moisture from the atmosphere and dissolves in it.

3) NaOH is highly alkaline. Carbon dioxide in the atmosphere is an acidic gas. Therefore NaOH reacts with carbon dioxide in the atmosphere and changes to sodium carbonate. 

4) Even the prepared solution is unstable because it is continuously absorbing carbon dioxide from the atmosphere while it is being used in titrations.

5) NaOH reacts with glass, so that if it is kept in a glass bottle with a glass stopper for a long time, the stopper may become fused to the bottle and the bottle cannot be opened without breaking. Dissolved glass will also contaminate the solution.