Answer:
The % yield = 61.3 %
The aspirin is impure, since the melting point was too low
Explanation:
<u>Step 1:</u> Data given
Mass of salicylic acid = 2.0 grams
Volume of acetic anhydride = 5.0 mL ( Density = 1.08 g/mL)
Molar mass of acetic anhydride =102.1 g/mol
Molar mass of salicylic acid = 138.2 g/mol
<u>Step 2:</u> The balanced equation
C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH
<u>Step 3:</u> Calculate moles of salicylic acid
Moles salicylic acid = mass salicylic acid / Molar mass salicylic acid
Moles salicylic acid = 2.0 grams /138.2 g/mol
Moles salicylic acid = 0.0145 moles
<u>Step 4: </u>Calculate moles of acetic anhydride
Mass of acetic anhydride = 1.08 g/mL * 5.0 mL = 5.4 grams
Moles acetic anhydride = 5.4 grams / 102.1 g/mol
Moles acetic anhydride = 0.0529 moles
<u>Step 5</u>: Calculate limting reactant
Mole ratio is 1:1 so since salicylic acid has the smallest number of moles, it's the limiting reactant
Salicylic acid will completely be consumed (0.0145 moles)
Acetic anhydride is in excess. There will 0.0145 moles be consumed.
There will remain 0.0529 -0.0145 = 0.0384 moles of acetic anhydride
<u>Step 6</u>: Calculate moles of aspirin
Since mole ratio is 1:1 there will be produced 0.0145 moles of aspirin
<u>Step 7:</u> Calculate mass of aspirin
Mass of aspirin = 0.0145 moles * 180.158 g/mol
Mass of aspirin = 2.61 grams = theoretical yield
<u>Step 8:</u> Calculate % yield
% yield = actual yield / theoretical yield
% yield = (1.6 grams / 2.61 grams)*100%
% yield = 61.3 %
Since the melting point of pure aspirin is 138-140, this means that the aspirin was impure. It's possible that the aspirin still has insoluble impurities in it.
