Respuesta :
A primary standard solid should be a very pure solid. NaOH does not meets this requirement because it is hygroscopic in nature.
A primary standard solid is a substance of known high purity (99.9% pure) which can be dissolved in a known volume of solvent that results in a primary standard solution. Primary standards solutions are reagents that are involved in chemical reactions. These compounds are often used to determine the unknown concentration of a solution that can undergo a chemical reaction with the primary standard compounds.
These compounds are extremely pure and are highly stable as well. Therefore, we can obtain pure solutions using these primary standard compounds.
Considering the case of NaOH, as it is hygroscopic in nature it attracts moisture from the air and its seen that its concentration keeps changing according to the environment around it and hence it cannot remain pure sample. Therefore we cannot rely on NaOH to the primary standard solid.
To know more about primary standard solid
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