I was wondering why all of the percentages like mass percent composition, percentage yield and percentage purity are calculated using masses.

Wouldn't it make more sense to use number of moles of the substance since we're counting the number of atoms in the molecules?

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    $\begingroup$ It is for the sake of convenience and practical purposes. Analytical balances or any other instrument cannot count the number of atoms/molecules, neither they are calibrated in terms of moles. All we can do is to measure its mass directly. Secondly, "measuring" moles assume that we know the exact molecular mass of that material. What if you make a new unknown product in a synthetic reaction? All you can do is to measure its mass directly and later characterize it. $\endgroup$ – M. Farooq Apr 15 at 5:36
  • $\begingroup$ Oh I see, thank you for your helpful answer! $\endgroup$ – ianc1339 Apr 15 at 6:16

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