[cœur_vaillant]

I've tried this question but just don't get it, can somebody help please !! 

Aspirin (C₉H₈O₄) is produced from salicylic acid (C₇H₆O₃) and acetic anhydride (C₄H₆O₃):

C₇H₆O₃ + C₄H₆O₃ --> C₉H₈O₄ + HC₂H₃O₂

(a) How much salicylic acid is required to produce 150 kg of  aspirin, assuming that all of acid is converted to aspirin?
(b) How much salicylic acid would be required if only 80% of the salicylic acid is converted into aspirin?

[macman104]

(a) How much salicylic acid is required to produce 150 kg of  aspirin, assuming that all of acid is converted to aspirin?

How many moles is 150kg of aspirin?  How many moles of salicylic acid does it take to make 1 mole of aspirin (hint, your reaction equation has the answer)?

(b) How much salicylic acid would be required if only 80% of the salicylic acid is converted into aspirin?

You need the answer to the first part of your question before you can tackle this.

[cœur_vaillant]

well, 150kg of aspirin would be ~ 832.48 mol (150kg/0.018017kg).

but then i dont know how you would find how many moles of salicylic acid it would take to make 1 mole of aspirin?

unless perhaps it would be the same since the molar ratio is 1:1 ?

[macman104]

well, 150kg of aspirin would be ~ 832.48 mol (150kg/0.018017kg).

but then i dont know how you would find how many moles of salicylic acid it would take to make 1 mole of aspirin?

unless perhaps it would be the same since the molar ratio is 1:1 ?

Indeed, in your reaction equation (which is balanaced), the molar ratio is 1:1.  This means that 1 mole of salicylic acid will create 1 mole of aspirin (as long as the other reactants are present in enough quantity).  With that information, can you calculate how many moles you will need now to make up for the 80% of salicylic acid in the second part?

[cœur_vaillant]

OK so i get the part that salicylic acid and aspirin are in a 1:1 ratio

and i figured out that there are 834.54 mol of aspirin present (can i get a 2nd opinion on this one )

so, i would find out how many grams there are of aspirin by mulitiplying # moles by molar mass

= 834.54g x 180.17g/mol =(approx.) 15036g =~ 15.036 kg of aspirin and thus 15.036kg of salicylic acid required since the two are in a 1:1 molar ratio.

other than probably messing up the SF, is that correct ? Thanks in advance 

[DrCMS]

You're making a very simple question difficult by not thinking clearly and contadicting yourself.

Try this

A+B ->  C + D

1 mole of A reacts with 1 mole of B to give 1 mole of C and 1 mole of D.

If 1 mole of A weighs 50, B weighs 40, C weighs 75 and D weighs 15

then 50g of A + 40g of B give 75g of C and 15g of D.

So to get 150g of C we need 100g of A and 80g of B.

If only 50% of A reacts we'd need 200g of A to make 150g of C

Now apply this to your problem.

Remember moles are not the same as grams and take care with your maths your were out by a factor of 10 before.

[Borek]

Funny thing...

C₇H₆O₃ + C₄H₆O₃ -> C₉H₈O₄ + HC₂H₃O₂

20C₇H₆O₃ + 10C₄H₆O₃ -> 18C₉H₈O₄ + 9HC₂H₃O₂

31C₇H₆O₃ + 11C₄H₆O₃ -> 27C₉H₈O₄ + 9HC₂H₃O₂

14C₇H₆O₃ + 4C₄H₆O₃ -> 12C₉H₈O₄ + 3HC₂H₃O₂

and so on...

cœur_vaillant: don't worry, these have no meaning, although technically they are correctly balanced.