Salicylic Acid and Acetic Anhydride Reaction Calculation

Calculating the Limiting Reactant

Salicylic acid (C7H6O3) reacts with acetic anhydride (C4H6O3) to form acetylsalicylic acid (C9H8O4).

In order to understand what the limiting reactant is, we need to convert the masses of reactants into moles. The molecular masses are:

C7H6O3 = 138 g/mol

C4H6O3 = 100 g/mol


Converting masses into moles:

70 g C7H6O3 x (1 mol / 138 g) = 0.5 mol C7H6O3

80 g C4H6O3 x (1 mol / 100 g) = 0.8 mol C4H6O3


In the reaction, 2 moles of C7H6O3 are necessary to react with 1 mol of C4H6O3. Following this ratio:

0.8 mol C4H6O3 x (2 mol C7H6O3 / 1 mol C4H6O3) = 1.6 mol C7H6O3


We have only 0.5 mol of C7H6O3, meaning we don't have enough salicylic acid. Therefore, salicylic acid (C7H6O3) is the limiting reactant.

What is the limiting reactant if 70.0 g of C7H6O3 and 80.0 g of C4H6O3 react? Answer: B) Salicylic acid Explanation: The limiting reactant is salicylic acid according to the calculations performed.
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