A couple questions about the production of aspirin

[Unknown_one]

Questions
-Sulfuric acid is a catalyst in the reaction of salicylic acid with acetic anhydride. How might a chemist prove that sulfuric
acid acts as a catalyst, rather than as a reactant, in this reaction?

-Draw the structural formula of aspirin. Indicate and name two functional groups present in the molecule.

-A commercial ‘Aspro’ tablet contains 300 mg of aspirin. Calculate the number of these tablets that you could make
from the aspirin produced in this experiment.

- Assuming the salicylic acid is the limiting reactant in your synthesis of aspirin, calculate the maximum mass of aspirin
that could be theoretically obtained using the original 3 g of salicylic acid.

- Use your answer to Question 4 to calculate the percentage yield of aspirin for this experiment  (the mass actually
obtained, expressed as a percentage of the maximum possible mass).

Umm. Can anyone help me with these questions. Specifically the second one?
Im doing a practical on aspirin, but its not this one, so I was looking to have a head start on the others.
That way I can fully understand how to make it properly. =)

The things that are used are
3 g salicylic acid
• 10 mL acetic anhydride
• 1 mL concentrated sulfuric acid

Could a very intelligent past Chemistry student, help me?

[Cappuccinos]

I'm not very intelligent, but I'll give it a go

1) Hmm I'm not quite sure if you have to prove this with calculations, but sulfuric acid only increases the the rate of reaction,  not the yield. So therefore, its a catalyst.

2) The two functional groups in aspirin (Acetylsalicylic acid) are the carboxy group (COOH) and an ester group (O - C = O)
Ceebs drawing, but so here it is.     http://www.medicalook.com/molecular/aspirin.gif Can you see the two functional groups?

3) I think you need results to do this question. So say your obtained mass of 3.7g for aspirin. One 'Aspro' tablet contains 0.3 g. So you divide 3.7 g by 0.3 which gives you 12.3. So you could make 12 tablets.

4)



Its a 1:1 ratio so therefore






(I got the molar masses of google, not the data book)

5) Again you need results.  To calculate percentage yield


Hope that helped 

[BlueSky_3]

I told you how to do the first one mate 

[Unknown_one]

Hey I was wondering?
Would it affect the yield through the fact that as it lowers the activation energy, the fact that if it is not present then the activation energy is much higher and therefore as a result be unable to react therefore producing a lower/ no product yield?
Is that possible? Its just a logical thought that I was ponddering about whilst reading about activation energy.
In addition, how do I prove this
How might a chemist prove that sulfuric
acid acts as a catalyst, rather than as a reactant, in this reaction?

In the solution, there is ethanoic acid, so titration it seems is out of the question..
Im not really sure...

[BlueSky_3]

Nah....the ethanoic acid is used up (i.e was the limiting reagent remember) and we only titrate the filtrate containing the H2SO4. And for the former, no Steph243 was right in that the yield is not affected. Yeah if catalyst wasn't present then activation energy would be higher but the reaction would take place anyway though it might take ages.

[thushan]

hmm, perhaps throw a known amount of H2SO4 into the reaction mixture, let the reaction occur, add some OH- to increase pH to about say 4-5, then add Ba2+ ions to precipitate SO4 2- ions. if n(SO4 2-) = n(H2SO4 added), then H2SO4 is acting as a catalyst.

[BlueSky_3]

What's the advantage of increasing the pH?

[thushan]

so that you're sure you're precipitating out BaSO4 and not Ba(HSO4)2

[Unknown_one]

So to confirm, it doesn't affect the yield.
So basically the catalyst here simply speed up the reaction, rather than providing a lowering of energy to complete the reaction?
I assumed that if it didnt reach the critical activation level energy, the reaction wouldn't occur, hence it would only partially occur?
Or in this case as the experiment was done over one period, the fact that if we didnt have sulfuric acid would lead to a lower yield as the crystalisation wouldn't have fully completed for the fact that the activation energy was lower and therefore not enough to produce a faster reaction rate, which would hence lead to a lower amount of crystalisation, which = a lower percentage yield?
Can anyone correct me on this?

[BlueSky_3]

so that you're sure you're precipitating out BaSO4 and not Ba(HSO4)2

Hmm...that's out of the scope of the course, so I doubt they would be looking for that as an answer.

[thushan]

out of the unit 3 course anyway...would be valid if they integrated unit 3 and 4 into one exam though
oh wait, that's next year

[mharris13]

Did this exact SAC last week and got 25/25 for it.
For the catalyst question:
I simply said perform experiment without sulfuric acid and record time taken to complete reaction, then perform the same experiment in the presence of the sulfuric acid and observe the time taken has lowered.   
I have also made a PDF of the reaction pathway for it with all functional groups marked and if you PM me I will be happy to send you a copy.