Question

Calculate the percent yield of aspirin obtained when138mg of salicylic acid, 0.3 ml of acetic anhydride is used and 0.110 gm of aspirin is obtained, what would be % yield?

Answer 1

salicylic acid + acetic anhydride .................> Asprin + acetic acid

1mole of salicylic acid requires 1 mole acetic anhydride

no. of moles of salicylic acid = (wt/mol.wt) = (138*10^-3/138) = 0.001 moles

no. of moles of acetic anhydride = PV/RT = 1*0.0003/0.0821*273 = 0.99 moles

so salicylic acid is limiting reagent

0.001 moles of aspirin forms

weight of aspirin = no.of moles of aspirin* mol.wt = 0.001*180.1 = 0.180 gm.

% of yield = (practical yield/theoritical yield)*100

                    = ( 0.110/0.180)*100 = 61.1 %