Why is sodium tetraborate decahydrate a good primary standard?
Corrie writes Here’s what Jenkin had to say, in an answer to an earlier question on this subject: Jenkin says A primary standard is a substance which can be weighed out and made into a solution of exact, known concentration. So it must be available in a reliably pure state. It will not, ideally, contain water of crystallisation because this invariably throws doubt on its absolute composition; it might absorb or release unknown amounts of this water. It should not be affected by exposure to air, meaning it should not react with oxygen, carbon dioxide or water vapour. In practice, very few substances make ideal primary standards and compromises have to be made. The particular advantages of sodium tetraborate decahydrate are: 1. A relatively large molar mass (190.72), which means a larger mass must be weighed out than, for instance, anhydrous sodium carbonate, providing greater accuracy. 2. It easily commercially available in very pure form. 3. Heating to a constant mass is not required (
