Post-Laboratory Questions Use the spaces provided for the ansuers and additional
ID: 558953 • Letter: P
Question
Post-Laboratory Questions Use the spaces provided for the ansuers and additional paper if necessary. t performing this experiment misread Step 3 and added 0.40 mL of acetic anhydride, instead this procedural error affect the theoretical yield of her preparation? Briefly explain. of 4.0 ml. Did 2 After completing Step 9 of the Procedure, a student noticed that, although his aspirin crystals appeared to be dry, the filter paper was still damp, He went ahead and performed the weighing directed in Step 10, then went on to finish the experiment. Did the damp filter paper affect any of the following? In each case, briefly explain your answer (a) theoretical yield (b) calculated actual yield (c) calculated percent yield
Explanation / Answer
1) Synthesis of Aspirin:
Salicylic acid+acetic anhydride ---->Aspirin+ acetic acid
Molar mass of Salicylic acid=138g/mol
Molar mass of acetic anhydride=102 g/mol,density=1.08g/ml
As they react in 1:1 molar ratio So, if the student takes 0.4 ml of acetic anhydride ,mol of acetic anhydride added to the reaction=0.4ml*(1.08g/ml)/(102 g/mol)=0.00423 mol
Actual mol of acetic anhydride to be added=4.0ml*(1.08g/ml)/(102 g/mol)=0.0423 mol
generally 2-2.5 g of salicylic acid is added to 5ml of acetic anhydride,so mol of salicylic acid added=2.5g/138g/mol=0.0181 mol (<0.0423 mol) so ,this one is the limiting reactant
Acetic anhydride is take in excess and remaining of it is destroyed after completion of the reaction,as it reacts with water to give acetic acid.Aspirin is separated by recrystallization.
So, the theoretical yield will not be affected as 0.0181 mol of salicylic acid will be assumed to react with 0.0181 mol of acetic anhydride to produce 0.0181 mol of product