# Question #b2485

Sep 29, 2014

There are three steps to answering this question correctly:

1. Write a balanced reaction for the chemical process
2. Calculate the number of moles of each reactant in order to identify which is the limiting reactant (smallest number of required moles)
3. Calculate the theoretical yield (assuming perfect 100% reaction) of the product based on the moles of limiting reactant.

The balanced reaction in this case is
${C}_{4} {H}_{6} {O}_{3} + {C}_{7} {H}_{6} {O}_{3} \leftrightarrow {C}_{9} {H}_{8} {O}_{4} + {C}_{2} {H}_{4} {O}_{2}$
so we require equal numbers of moles of acetic anhydride and salicylic acid. The products are acetylsalicylic acid (aspirin) and acetic acid.

The molar mass of salicylic acid is 138.121 g/mol, so 0.9457 g corresponds to 0.006847 mol. For acetic anhydride, we need to look up both the density (1.082 g/mL) and the molar mass (102.09 g/mol) to calculate the number of moles in 3.52 mL:
$\frac{3.53 m L \times 1.082 \frac{g}{m L}}{102.09 \frac{g}{m o l}} = 0.0374 m o l$

Therefore, the limiting reagent is salicylic acid.

The theoretical yield of acetylsalicylic acid (180.157 g/mol) is
$0.006847 m o l \times 180.157 \frac{g}{m o l} = 1.234 g$