This experiment calls for 5.0 mL of acetic anhydride. Acetic anhydride has a density of exactly 1.08 g/mL. What is the mass of acetic anhydride in this experiment? Use the answer obtained above to determine the number of moles of acetic anhydride used in this experiment. The formula for acetic anhydride is C4H6O3. The experiment calls for 2.00 grams of salicylic acid. How many moles of salicylic acid is this? The formula of salicylic acid is C7H6O3. Write the balanced reaction for this experiment (use the last equation on the bottom of page 1 of the manual as a starting point). Using the answers for questions 3 & 4, how many moles of aspirin are made? According to the reaction on the first page of the manual, one molecule of salicylic acid reacts with one molecule of acetic anhydride. This means that if fewer moles of one are present than the other, the one with fewer moles will be used up first and some of it will be leftover at the end of the reaction. Which of the two reactants will be used up first in this reaction? (This is called the limiting reactant because it limits the amount of aspirin that can be made). Using the number of moles of the limiting reactant and the number of moles of aspirin produced, calculate how many grams of aspirin can be prepared. This is called the theoretical yield. The theoretical yield is 2.61 grams.
The Correct Answer and Explanation is:
Answer:
- Mass of acetic anhydride:
Density = 1.08 g/mL
Volume = 5.0 mL
Mass = 1.08 g/mL × 5.0 mL = 5.40 g - Moles of acetic anhydride:
Molar mass of acetic anhydride (C₄H₆O₃) = 102.09 g/mol
Moles = 5.40 g ÷ 102.09 g/mol = 0.0529 mol - Moles of salicylic acid:
Given mass = 2.00 g
Molar mass of salicylic acid (C₇H₆O₃) = 138.12 g/mol
Moles = 2.00 g ÷ 138.12 g/mol = 0.0145 mol - Balanced chemical reaction:
C₇H₆O₃ (salicylic acid) + C₄H₆O₃ (acetic anhydride) → C₉H₈O₄ (aspirin) + CH₃COOH (acetic acid) - Limiting reactant:
According to the balanced reaction, one mole of salicylic acid reacts with one mole of acetic anhydride.
Moles of salicylic acid = 0.0145 mol
Moles of acetic anhydride = 0.0529 mol
Since salicylic acid is present in the smaller amount, it is the limiting reactant. - Moles of aspirin produced:
Based on the 1:1 mole ratio, 0.0145 mol of salicylic acid produces 0.0145 mol of aspirin - Theoretical yield of aspirin (C₉H₈O₄):
Molar mass of aspirin = 180.16 g/mol
Mass = 0.0145 mol × 180.16 g/mol = 2.61 g
Explanation (300 words):
Acetic anhydride is a liquid with a density of 1.08 g/mL. Multiplying its density by the given volume of 5.0 mL results in a mass of 5.40 g. To find the number of moles, the mass is divided by its molar mass, which is 102.09 g/mol. This results in 0.0529 mol of acetic anhydride.
The experiment also involves salicylic acid, a solid reagent. Given 2.00 grams of salicylic acid and its molar mass of 138.12 g/mol, the number of moles can be found by dividing the mass by the molar mass. This yields 0.0145 mol of salicylic acid.
The reaction between salicylic acid and acetic anhydride forms aspirin (acetylsalicylic acid) and acetic acid. The balanced chemical equation shows a 1:1 molar ratio between salicylic acid and acetic anhydride, indicating that one mole of each reactant produces one mole of aspirin. In this scenario, salicylic acid has the smaller number of moles, making it the limiting reactant. The limiting reactant determines the maximum possible amount of product that can be formed.
Because the mole ratio of salicylic acid to aspirin is 1:1, the number of moles of aspirin formed is equal to the number of moles of salicylic acid used: 0.0145 mol. The molar mass of aspirin is 180.16 g/mol, so the theoretical mass of aspirin that could be produced is calculated by multiplying the number of moles by the molar mass. This gives a theoretical yield of 2.61 grams of aspirin.
