Gce Model Questions Vol1 2022 Chemistry Question 9

Ethanol (M = 46.07 g·mol⁻¹) is oxidised to acetaldehyde (M = 44.05 g·mol⁻¹) using pyridinium chlorochromate (PCC, M = 322.9 g·mol⁻¹). In a laboratory experiment, 5.00 g of ethanol is reacted with 20.0 g of PCC (excess). The reaction proceeds with 1:1 stoichiometry (1 mol ethanol : 1 mol PCC). After work‑up, 3.20 g of acetaldehyde is isolated, corresponding to a 67% overall recovery. (a) Calculate the theoretical mass of acetaldehyde that could be formed from the given ethanol. (b) Determine the overall percent yield based on the isolated mass. (c) If the oxidation were instead carried out with acidic dichromate (Cr₂O₇²⁻) in aqueous solution, 10% of the ethanol would be converted to ethanoic acid (M = 60.05 g·mol⁻¹) and the remaining ethanol would be fully converted to acetaldehyde, with 100% isolation of the acetaldehyde. What mass of acetaldehyde would be obtained in this alternative method? Compare the two methods.