Question

How much acetic anhydride is needed to produce 4.27g of acetylsalicylic acid, assuming that you have unlimted salicylic acid? Will you still be able to produce this amount of acetylsalicylic acid if you use your calculated amount of acetic anhydride, but only have 3.71g of salicylic acid?

Answer 1

Sol.

acetic anhydride + salicylic acid ----->

acetylsalicylic acid + acetic acid

As mass of acetylsalicylic acid   = 4.27 g

molar mass of acetylsalicylic acid   = 180.158 g / mol

So , moles of acetylsalicylic acid = 4.27 / 180.158

= 0.0237 mol

From reaction ,

moles of acetylsalicylic acid

= moles of acetic anhydride = 0.0237 mol  

As molar mass of acetic anhydride = 102.09 g / mol

So, mass of acetic anhydride needed to produce 4.27 g of acetylsalicylic acid  

= 0.0237 × 102.09

=   2.42 g   

Now , only 3.71 g of salicylic acid is used , so ,

mass of salicylic acid = 3.71 g

molar mass of salicylic acid = 138.121 g / mol

moles of salicylic acid = 3.71 / 138.121 = 0.0269 mol

From reaction , moles of acetylsalicylic acid  

= moles of salicylic acid = 0.0269 mol

As salicylic acid reactant produces more moles of acetylsalicylic acid than acetic anhydride  reactant ,so , limiting reactant is acetic anhydride and again , same amount of acetylsalicylic acid is produced , that is , 4.27 g