Practical investigations
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In the analysis of vinegars special study tutorial bit, it speaks of standardising strong alkalis as their concentrations can change in air. obviously this is bad when using them for titrations. I'm just confused by what you mean by standardising the alkali with a reliable acid?
Corrie writes ....
Standardising the alkali means titrating it with an acid of accurately known concentration, in order to find the exact concentration of the alkali being used in the vinegar titration. Strongly alkalis, like sodium hydroxide, cannot be obtained and weighed as very pure solids as they absorb and react with carbon dioxide in the air - even as they being weighed. Similarly, strongly alkaline solutions react with carbon dixoxide in air and their concentration slowly changes with time. They thus need to be 'standardised' just before use.
Acids used to make up such standard solutions have to be stable, available in very pure form and, preferably, be solids - so they can be weighed out easily. One such acid commonly used for this purpose is potassium hydrogenphthalate, KH(C8H4O4).
It reacts 1:1 with NaOH.
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updated: 21 January 2008
