April 26, 2015

Homework Help: chemistry - synthesis of aspirin

Posted by Priscilla on Saturday, April 7, 2012 at 1:31pm.

wanted to calculate the theoretical and actual yield of aspirin.

mass of salicylic acid = 2.005 g

But isn't salicylic acid differ. from acetic acid? If so, how do we find the mass of acetic acid in this experiment

volume of acetic anhydride = 4 ml

mass of acetic anhydride (use 1.08 g/ml for the liquid density) = (1.08 g/ml)(4 ml)= 4.32 g

moles of acetic anhydride ((CH3CO)2O; molar mass = 86 g) = 4.32 g / 86 g = .0502 mol

mass of filter paper = .196 g

mass of weighing tray = 1.900 g

mass of aspirin, filter paper, and weighing tray = 4.286 g

mass of aspirin = 2.19 g

moles of aspirin (C9H8O4; molar mass = 180 g) = 2.19 g / 180 g = .0121 mol

I know the percent yield is equal to the mass of actual yield divided by the theoretical yield and is multiplied by 100%. Also, there has to be a balanced equation in order to calculate the theoretical yield. But I'm a little confused on how to set up the balanced equation.
chemistry - synthesis of aspirin - DrBob222, Friday, April 6, 2012 at 4:55pm
1 mol acetic anhydride + 1 mol salicylic acid = 1 mol aspirin
I don't know the formulas (I could look them up but you probably have them) but the above tells you what you want to know. It's a 1:1 ratio throughout.
You will need to calculate the mols salicylic acid and mols acetic anhydride and determine the limiting reagent. Then you can calculate the theoretical yield.

chemistry - synthesis of aspirin - Priscilla, Friday, April 6, 2012 at 5:16pm
ok thank you

chemistry - synthesis of aspirin - Priscilla, Saturday, April 7, 2012 at 12:51pm
wait, I just have one quick question. I realized the equation for this experiment would be

C7H6O3 + C4H6O3 ----> C9H8O4 + C2H4O2

BUT... acetic acid's formula is C2H402 in molecular formula. Is the above equation right? Also, I realized after mixing salicylic acid and acetic anhydride this yields aspirin and acetic acid. But how do I obtain the mass of acetic acid?

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