OT - chemistry question

mmuk

help wanted - please!

''how much salicylic acid is needed to make one 300mg aspirin tablet''

molar mass salicylic = 138 1 mole = 2.174
mm aspirin = 180 1 mole = 1.667

any chemists/chemistry students out there?

cheers

Mike

Mike67

If you're making it this way:

C7H6O3 (Salicylic acid) + C4H6O3 (Ethanoic anhydride) => C9H8O4 (Aspirin) + C2H4O2 (Acetic acid)

Then it's a 1 to 1 stoichiometry so you would need (2.174/1.667)x0.3g which in my book equates to 0.391g, assuming a perfect reaction.

Now I've got a headache

pbt150

Not sure that's right Mike.

.3 g /180.1 g/mol = 1.667 milli moles of aspirin in the tablet.

Assume 1:1 reaction that goes to completion.

1.667 mmoles x 138.1 g/mole = .230 g salicylic acid required.

mmuk

thanks gents - I have been struggling with that all night!

Mike

mmuk

a third source has come up with:

Salicylic acid + Ethanoic anhydride = aspirin + acetic acid
1 mol + 1 mol = 1 mol + 1 mol
138g + 102g = 180g + 60g

Therefore, if 138g of salicylic acid are needed to make 180g of aspirin, multiply by 1.6 and divide by 1000 to give you 300mg.

=230mg


for anyone who's interested!

MM

beverick

ZZZZZZZzzzzzzzzzzzzzzzzzzzz

Mike67

pbt150 wrote:

Not sure that's right Mike.

.3 g /180.1 g/mol = 1.667 milli moles of aspirin in the tablet.

Assume 1:1 reaction that goes to completion.

1.667 mmoles x 138.1 g/mole = .230 g salicylic acid required.

You are correct...read it far too quickly as usual and took the second numbers as the molar masses :oops: Sorry OP.

It then becomes (138/180)x300mg which does indeed = 0.23g (230mg).

Back to cycling I think

MattC59

After thinking back to my A-Level chemistry, I remembered it's Friday and gave up

Homer J

it would be easier to buy them.