Why can standard NaOH solutions not be stored for extended periods?

Answer 1

Both the above answers are correct. The strength of the sodium hydroxide will be reduced by its reaction with carbon dioxide in the air and if stored in a glass bottle it will attack the glass (by a neutralisation reaction with the silicon dioxide in the glass). If the solution is stored in a polythene bottle with negligible air space and used up once it is opened there is no problem with storage time. It is supplied like this by laboratory suppliers like Merk and doesn't come with a 'use by date'.

Answer 2

The answer is: I don't know.
If you keep the air out, then you don't have the problem of it reacting with the gases in the air.
If you keep it in the dark, you don't have the problem of any photoreactions taking place.
NaOH would react with glass, so you'll need to keep it in some container that it won't react with.

So, if you're keeping it in the dark, sealed, and in a non-reactive container, I don't know what the problem is.

Answer 3

Because NaOH reacts with the CO2 of the atmosphere

2NaOH + CO2 --> Na2CO3 + H2O