The method and the results are on the esterification lab. Do the analysis yourself first, then check the answers below.
Quick answer: Carboxylic acids react with alcohols, in the presence of concentrated sulfuric acid, to form esters and water in a reversible equilibrium. These answers go with the Chemistry 11-12 lab on esterification: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
The model answers use the sample data. The amounts follow from the titre and the blank correction; the equilibrium constant should be close to 4 at room temperature. Show every conversion from cm³ to dm³ and the factor of 10 for the dilution.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.3.9
Acid used = 0.100 − 0.0333 = 0.0667 mol, so ester = water = 0.0667 mol. Ethanol left = 0.0333 mol.
Question 4 Calculate Kc
Kc = (0.0667 × 0.0667) / (0.0333 × 0.0333) = 4.0. Volume cancels because the amounts of products and reactants are equal in number.
Question 5 Quenching and blank
Cooling and diluting slows the reaction so the equilibrium does not shift during titration. The catalyst is also an acid that reacts with NaOH, so the blank subtracts its contribution.
Question 6 Prediction with more ethanol
x² / [(0.100 − x)(0.200 − x)] = 4.0 gives 3x² − 1.2x + 0.08 = 0, so x = 0.0845 mol. Acid left = 0.0155 mol. In 25.0 cm³: 1.55 × 10⁻³ mol, so titre = 15.5 cm³ (blank excluded).
Question 7 Errors and improvements
The ester and ethanol are volatile, so some may escape; the indicator end point is judged by eye. Use a well-sealed condenser and a longer reflux time, and check equilibrium by repeating with a 60-minute sample.
