Question

preparation of acetylsalicyclic acid post lab question

4.52 grams of salicylic acid and 4.5 mL of acetic anhydride (density: 1.080 g/mL) are mixed together. 3.75 grams of acetylsalicylic acid are obtained in the reaction.

1.) What is the limiting reagent in this reaction? And Why?

2.) What is the theoretical yield of the reaction? Show the calculations.

3.) What is the percent yield of the reaction? Show the calculations

Answer 1

Acetic anhydride+ salicyclic acid ---> Aspirin ( Acetyl salicylic acid) +acetic acid

C4H6O3+C7H7O7---->C9H8O4+CH3COOH

Molecular weights : Acetic anhydride = 102 g/mol, salicyclic acid = 138g/mol, Asprin = 180 g/mol

Acetic acid = 60 g/mol

moles : Salicyclic acid = 4.52/ 138=0.033 , moles of acetic anhydride= volume* density/ molecular weight= 4.5*1.080/102 =0.048

Molar ratio as per the stoichiometry of reaction = 1:1

Moles of reactants as per the given data= 0.048: 0.033 =1.45: 1

So excess is acetic anhydride and limiting is salicyclic acid

Moles of acetyl salicylic acid, theoretical yield = 0.033

Mass of acetyl salicylic acid (Aspirin),theoretical yiled =0.033*180=5.94 gms

percent yiled= 100* actual yiled/ theoretical yield = 100*3.75/5.94=63.13%