If 2 g of salicylic acid is heated with 4 g of acetic anhydride, what is the theoretical yield ?
C7H6O3 + C4H6O3 --> C9H8O4 + C2H4O3
This is a limiting reagent problem. You know that because BOTH reactants are listed instead of just one.
1. Convert 2 g SA to moles. moles = gram/molar mass.
2. Convert 4 g acetic acid to moles. Same way.
3a. Convert moles SA to moles product.
3b. Convert moles acetic acid to product.
3c. It is more than likely than the answer from 3a and 3b will not be the same which means one of them is wrong. The correct answer, in limiting reagent problems, is ALWAYS the smaller value and the reagent producing that value is the limiting reagent.
4. Now convert the value from 3c to grams. g = moles x molar mass.
To determine the theoretical yield in a chemical reaction, we need to know the balanced chemical equation and the amount of each reactant.
In this reaction, salicylic acid (C7H6O3) reacts with acetic anhydride (C4H6O3) to produce aspirin (C9H8O4) and acetic acid (C2H4O3).
Based on the balanced equation, the molar ratio tells us that for every 1 mol of salicylic acid, we need 1 mol of acetic anhydride to produce 1 mol of aspirin.
First, we need to convert the given masses of salicylic acid and acetic anhydride into moles by using their respective molar masses:
Molar mass of salicylic acid (C7H6O3) = (7 * 12.01 g/mol) + (6 * 1.01 g/mol) + (3 * 16.00 g/mol) = 138.12 g/mol
Moles of salicylic acid = 2 g / 138.12 g/mol = 0.0145 mol
Molar mass of acetic anhydride (C4H6O3) = (4 * 12.01 g/mol) + (6 * 1.01 g/mol) + (3 * 16.00 g/mol) = 102.09 g/mol
Moles of acetic anhydride = 4 g / 102.09 g/mol = 0.0392 mol
Since the ratio between salicylic acid and acetic anhydride is 1:1 in the balanced equation, we can determine that 0.0145 mol of salicylic acid will react with 0.0145 mol of acetic anhydride to produce 0.0145 mol of aspirin.
Now, we need to convert the moles of aspirin into grams by using the molar mass of aspirin:
Molar mass of aspirin (C9H8O4) = (9 * 12.01 g/mol) + (8 * 1.01 g/mol) + (4 * 16.00 g/mol) = 180.16 g/mol
The theoretical yield of aspirin is given by:
Theoretical yield = 0.0145 mol * 180.16 g/mol = 2.61 g
Therefore, the theoretical yield of aspirin in this reaction is 2.61 grams.