How can the percentage purity of the aspirin I synthesised be more than 100%?

Question

During a lab session, I synthesised some aspirin. I worked out the theoretical moles of aspirin to be 5.551x10^-4 (0.100g/180.16) and my actual moles to be 5.1954x10^-4 (0.0936g/180.16).

So when I workout the percentage purity of my aspirin, it works out to be 106.8%. I use the formula: (actual moles/theoretical moles) X 100.

Am I doing something wrong? I not, how can it possibly be more than 100% pure? Would greatly appreciate explanations

Answer 1

This is not "purity"--this is % yield--insofar as I can make out.

My first response (edited here) was the following:

Answer is easy--first place to look, error in weighing--either reactant under-weighted, or product over-weighted.

Much more likely however is that your "Crude Product" is a mixture, perhaps solvent-reacted with reactant,

... and finally you have the question of whether you weighted on the same scale---especially in University Labs they tend not to need to keep precision very high for undergraduate lab....

So: (1) human error, (2) unaccounted for products

THEN I REALIZED YOU PLACED THE THEORETICAL YIELD IN THE NUMERATOR, NOT THE DENOMINATOR.

Looks like 100mg was theoretical yield--and actual yield was 90+ mg... this is not >100% yield.

So your yield would actually be 1.00/1.06 . . . which should exactly coincide, albeit different or of magnitidue, with your gross gramage-yield.... check it out again by taking reciprocal of your calculation.