[User1234]

In a experiment to determine the solubility product of sodium hydroxide, one of the first few procedure is to prepare Calcium Hydroxide early.
The prepared solution is then transferred to mix with hydrocloric acid with burette.
I'm wondering why the solution must be prepared early.

Thanks for any reply.

[Johnny010]

Most likely to ensure the Calcium hydroxide has been properly formed?
How was it prepared?

[renge ishyo]

If he means why must calcium hydroxide be prepared "fresh" on the day you perform your experiment as opposed to letting it sit around in a bottle for awhile like HCl then the reason for that is that it will react with carbon dioxide in the atmosphere if it is exposed to it for a short period of time (it can form calcium carbonate, bicarbonate ion, etc.). If you leave a bottle of a "hydroxide base" open overnight you have to toss it the next day and make a new batch. I don't know what he means by preparing it "early" though, so I may be misunderstanding the question.