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chemistry - synthesis of aspirin

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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  1. Yes, what you've written is right. Why are you worrying about acetic acid? That's a product but you want theoretical yield of aspirin so how much acetic acid is produced is of no interest. If you wanted theoretical yield of acetic acid we would be interested in that but otherwise it's superfluous information. In fact, you don't need it in the equation except it's nice to have the equation balanced. The only part you care about is 1 mol salicylic acid = 1 mol acetic anhydride = 1 mol aspirin. Now find the limiting reagent and go from there.

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  2. Okay i understand from what you said. But in my lab report, they stated the mass of acetic acid and from that I would have to calculate the number of moles of acetic acid. But since you state acetic acid is just a product should i leave these two questions blank then

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  3. Now you're confusing me. I have made some assumptions in answering your questions. Some of those assumptions may not be right if the questions change; please type everything in and I can have ALL of the information at one time instead of getting it in bits and pieces. From what you say in the last post it may very well make a difference how much CH3COOH is formed.

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