Mass given % Yield

Question

I am completely lost on this hw so any help would be greatly appreciated. Please and thank you!

What mass of aspirin(C9H8O4) is produced from 86.4g of C7H6O3 assuming 95.0% yield from the reaction below?

C7H6O3(s) + C4H6O3(s) --> C9H8O4(s) + HC2H3O2(aq)

Answer 1

Since you are given the mass of only one reactant (C₇H₆O₃), we can assume the other reactant (C₄H₆O₃) is in excess. As a side note, the reaction as written wouldn't take place because you have shown both reactants to be in the solid (s) phase. They both should be in the aqueous (aq) phase (minor point for this exercise).

molar mass C₇H₆O₃ = 138 g

molar mass C₉H₈O₄ = 180. g

Theoretical yield of C₉H₈O₄ = 86.4 g C₇H₆O₃ x 1 mol / 138 g x 1 mol C₉H₈O₄ / mol C₇H₆O₃ = 0.626 mols

0.626 mols C₉H₈O₄ x 180. g / mol = 113 g C₉H₈O₄ = theoretical yield

With a 95.0% yield, the mass of C9H8O4 will be 0.95 x 113 g = 107 g (3 sig. figs.)

Answer 2

I see that the reaction is balanced as written. The stoichiometry is (86.4g C₇H₆O₃) • (1 mole C₇H₆O₃ / 138.1g C₇H₆O₃) • (1 mole C₉H₈O₄ / 1 mole C₇H₆O₃) • (180.2g C₉H₈O₄ / 1 mole C₉H₈O₄) = 112.₇ g C₉H₈O₄ theoretical yield. Actual 95.0% of this is 107 g.