Making ethanol by the hydration of ethene
4 marks · NormalThe table below shows different industrial runs for the hydration of ethene, with the corresponding conditions and yields.
| Run | Temperature (°C) | Pressure (atm) | Catalyst | Yield of ethanol (%) |
|---|---|---|---|---|
| A | 270 | 60 | phosphoric acid | 70 |
| B | 300 | 65 | phosphoric acid | 81 |
| C | 325 | 70 | phosphoric acid | 84 |
| D | 350 | 55 | phosphoric acid | 77 |
Identify the run with the highest ethanol yield.
State the temperature and pressure for this best-yield run.
Describe how increasing temperature affected yield between runs A, B and C.
Suggest one reason why the yield in run D is lower than in run C, even though the temperature is higher.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Run C
(b) 325°C, 70 atmospheres
(c) Yield increases as temperature increases from runs A to C. · must show yield increases
(d) Yield may decrease at too high temperatures because equilibrium shifts, or because more ethanol may decompose at higher temperatures. · must show equilibrium, decomposition, lower pressure
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies run C as best-yield run.
B2 (b) · 1 mark · States correct temperature and pressure for run C: 325°C, 70 atm.
M1 (c) · 1 mark · Correctly observes that yield increases from runs A to C with increasing temperature.
B3 (d) · 1 mark · Provides a valid reasoning for lower yield in run D (e.g., too high a temperature may shift equilibrium, cause decomposition, or lower pressure reduces yield).
Worked solution
(a) Run C
(b) 325°C and 70 atmospheres
(c) As temperature increased from run A (270°C) to run C (325°C), the ethanol yield also increased.
(d) In run D, although the temperature is higher (350°C), the pressure is lower, and higher temperatures may decrease yield due to equilibrium position or ethanol decomposition.