While studying for my chemistry midterm today, I encountered this question:

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Aspirin is produced by the reaction of salicylic acid (molar mass = 138.1 g/mol) and acetic anhydride (molar mass = 102.1 g/mol).

C7H6O3(s) + C4H6O3(l) → C9H8O4(s) + C2H4O2(l)

If you mix 10.0 grams of each reactant, how many grams of aspirin (M = 180.2 g/mol) can theoretically by
obtained?

a. 7.30 g
b. 7.66 g
c. 9.32 g
d. 12.7 g
e. 13.0 g

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Reading that, I went to myself, Waitaminute, isn’t salicylic acid one of the main active ingredients in acne medication? So, if asprin contains salicylic acid, is there a way to use it for acne treatment?

And apparently there is.

“The active ingredient in aspirin is acetylsalicylic acid. In the presence of water at a neutral pH, this compound will hydrolyze to salicylic acid and acetic acid to a very small extent. It is likely that aspirin masks are only safe because this hydrolysis is very minimal in water of a neutral pH.

It is precisely because salicylic acid is lipid-soluble that it is so effective treating acne at very low concentrations. The acid is able to dissolve in the sebum and penetrate into pores to exert its exfoliating effects. ” – Anon (General consensus found in various places says this)

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So there you go. Asprin can be used to treat acne. I guess I should work out the problem since it’s here:

1) Find grams of asprin with 10.0g C7H6O3 (molar mass = 138.1g/mol)

10.0g C7H6O3 * (1 mol C7H6O3 / 138.1g C7H6O3) * (180.2g asprin / 1 mol C7H6O3)

= 13.05 g asprin = 13.1 g asprin

2) Find grams of asprin with 10.0g C4H6O3 (molar mass = 102.1g/mol)

10.0g C4H6O3 * (1 mol C4H6O3 / 102.1g C4H6O3) * (180.2g asprin / 1 mol C4H6O3)

= 17.65g asprin = 17.7 g asprin

3) Which produces the least amount of asprin?

C7H6O3. So, 10.0g of C7H6O3 and 10g of C4H603 will only give 13.1g of asprin.

Answer E.