Making Standard Solutions (1 Viewer)

Jojofelyx

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Hey, when I make a standard solution, and I leave it stoppered, even if its a secondary standard (like KMnO4 or NaOH). Will this change my results too much (in terms of the determined concentration of the standard solution) because of the hydrophilic nature of NaOH for example (although its stoppered).
 

CM_Tutor

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The problem of NaOH (s) being hygrascopic and absorbing water from the air means that NaOH cannot be used as a primary standard because you can accurately measure out a sample but you can't know how much of it is NaOH and how much is water. This is usually not a problem with the solution. However, a solution of NaOH will absorb CO2 from the air and so its concentration will not remain constant. Whether the amount by which it changes is a significant problem depends on the intended use.

When using a standardised NaOH for titrations, best practice is to standardise it with a known solution of an acid prior to use. However, this is not essential if the time since it was last standardised is short. If it has sat unused for a week, I'd probably re-standardise. Overnight is probably not a problem.
 

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