Question

You start with 1.956 g of salicylic acid and 5.00 mL of acetic anhydride. Find the limiting reagent and calculate the theoretical yield of Aspirin in grams.

C₄H₆O₃ + C₇H₆O₃ --> C₉H₈O₄

The MM for aspirin = 180.16 g/mol
MM for Salicylic acid = 138.12 g/mol
MM for acetic anhydride = 102.09 g/mol

Answer 1

moles of Salicylic acid = mass/ Molecular weight= 1.956/138.12=0.014162

Mass of acetic anhydride in 5ml = Volume* density= 5*1.082 g/cc =5.41 gm

Moles of acetic anhydride= 5.41/102.09=0.053

From the stoichiometry 1 mole of salicylic acid reacts with 1 mole of acetic anhydride to give 1 mole of asporin

So molar ratio of Salicyclic acid : acetic anhydrdie :1:1

Actual molar ratio : 0.014162 : 0.053 =1: 3.74

Hence excess is acetic anhydride and salicyclic acid is limitinng reactant and it decides the extent of Aspirin formed.

Moles of asprin formed= 0.014162., mass of asprin= 0.014162*180.16=2.549 gm