Asprin, C9H8O4, is prepared by reacting salicylic acid, C7H6O3, with acetic anhydride, C4H6O3, in the reaction

C7H6O3(s) + C4H6O3(l) -> C9H8O4(s) + C2H4O2(l)
A student is told to prepare 45.0 g of aspirin. She is also told to use a 55.0% excess of the acetic anhydride and to expect to get an 85.0% yield in the reaction. How many grams of each reactant should she use?

Can someone please give me a brief outline what I need to do to solve this?

You want 45 g aspirin. How many moles of asprin is that?

You want that number of moles/.85 of salicytic acid, and aspirin (numbermolesAspirin/.85) * 1.55 of the acetic anhydride. Think this out, repost if you have questions.

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To solve this problem, you can follow these steps:

1. Start by determining the number of moles of aspirin you need. You are given that you want 45.0 grams of aspirin. To convert grams to moles, you use the molar mass of aspirin. The molar mass of aspirin (C9H8O4) is 180.16 g/mol. So, 45.0 g aspirin / 180.16 g/mol = 0.2496 mol aspirin.

2. Since the yield of the reaction is expected to be 85.0%, you need to adjust the amount of salicylic acid and acetic anhydride accordingly. You divide the number of moles of aspirin (0.2496 mol) by the yield (0.85) to get the theoretical number of moles of salicylic acid needed. So, 0.2496 mol aspirin / 0.85 = 0.2936 mol salicylic acid.

3. Next, calculate the number of moles of acetic anhydride needed. You are told to use a 55.0% excess of acetic anhydride. This means you need to multiply the number of moles of aspirin (0.2496 mol) by 1.55 to get the excess amount of acetic anhydride. So, 0.2496 mol aspirin * 1.55 = 0.386 mol acetic anhydride.

4. Now, you need to convert the number of moles of salicylic acid and acetic anhydride into grams. To do this, you multiply the number of moles by their respective molar masses. The molar mass of salicylic acid (C7H6O3) is 138.12 g/mol, so 0.2936 mol salicylic acid * 138.12 g/mol = 40.54 g salicylic acid. The molar mass of acetic anhydride (C4H6O3) is 102.09 g/mol, so 0.386 mol acetic anhydride * 102.09 g/mol = 39.47 g acetic anhydride.

Therefore, the student should use 40.54 grams of salicylic acid and 39.47 grams of acetic anhydride to prepare 45.0 grams of aspirin.

how'd you get 1.55g acetic anhydride?

C7H6O3 (s) + C4H6O3 (l) -> C9H8O4 (s) + C2H4O2 (l)

molar masses:
salicylic acid, C7H6O3 = 138.12 g/mol
acetic anhydride, C4H6O3 = 102.09 g/mol
Asprin, C9H8O4 = 180.157 g/mol

For this problem calculate the moles of aspirin obtained from 45.0 g. This represents an 85.0% yield.

% yield = (mass aspirin produced)/(theoretical mass aspirin)](100%)

Using those numbers above, calculate the theoretical mass of aspirin needed. Once you have that number you can calculate the theoretical moles of aspirin. Use the chemical equation to determine the mass of salicylic acid needed to obtain the 45 grams.

Moles aspirin = moles salicylic acid = moles acetic anhydride.

Once you have the moles of acetic acid then you can determine the 55% excess by multiplying by 1.55(moles acetic anhydride).

2 C7H6O3 + 1 C4H6O3 -> 2 C9H8O4 + H2O

45.0 g / 0.85 = 52.9 g theoretical yield.

52.9 g C9H8O4 x (1 mole / 180.2g) = 0.294 moles aspirin

0.294 moles aspirin x (2 moles C7H6O3 / 2 moles aspirin) x (138.1 g C7H6O3 / mole C7H6O3) = 40.6 g salicylic acid.

0.294 moles aspirin x (1 mole C4H6O3 / 2 moles aspirin) x (102.1 g C4H6O3 / mole C4H6O3) = 15.0 g acetic anhydride.

but you need 55% excess C4H6O3... 1.55 x 15.0 g = 23.3 g acetic anhydride

I think the guy/girl was supposed to put .55 but accidently put a one insead of a zero and tried to figure it out like that. The actual answer is:

0.55 x 15.0 g = 8.25 g acetic anhydride