Compare fermentation and catalytic ethene hydration
Weigh feedstock, rate, operating conditions and separation, using the needs of a supplied production scenario.
Exam scope and assessment notes
Extended only (Supplement) · Chemistry 0971, 2026–2028. Cambridge states that IGCSE 0971 has the same subject content as IGCSE 0620, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall the reactants and full conditions for fermentation and hydration.
- Distinguish a renewable feedstock from guaranteed sustainable production.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which feedstock pairing matches the two routes?
What you will learn
- Describe advantages and disadvantages of both required ethanol-manufacture routes.
- Use supplied priorities to make a qualified route choice rather than declaring one universally better.
Compare the same dimensions
Fermentation can use glucose from renewable crops and runs at 25–35°C, avoiding the hydration route's high operating temperature and pressure. Against that, it is comparatively slow, is commonly described as a batch process, and gives a dilute aqueous mixture requiring separation to concentrate ethanol. Crop feedstocks need land and other resources; renewable supply is not proof that every production system has no environmental costs.
Catalytic ethene hydration is comparatively fast and can run continuously, and avoids the crop/yeast fermentation stage. Its crude ethanol stream still needs purification; the reaction is not a direct guarantee of pure isolated ethanol. It requires 300°C, 6000 kPa / 60 atm and an acid catalyst, so energy and suitable high-pressure equipment matter. Conventional ethene is commonly obtained from petroleum processing, a non-renewable feedstock route; do not claim every possible ethene source must be petroleum.
Separate a comparison from a universal guarantee
Neither route's balanced equation determines actual conversion, operating costs or final product purity. Fermentation's low reaction temperature does not remove all energy demand, because separation and other plant steps also matter. Hydration's continuous operation does not establish that every factory achieves the same output or that no purification is required.
For a decision, compare the stated feedstock availability, output rate, equipment and product-concentration needs. Explain the advantage that fits the scenario and the disadvantage that remains. Use a supplied table for any numerical claim rather than inventing a universal cost or percentage yield.
Pause and explain
Which is a justified manufacture comparison?
Worked example
A hypothetical site has plentiful crop-derived glucose and prioritises a renewable feedstock over rapid continuous output. Recommend a route and state two limitations.
Show the worked solution
- Fermentation uses the available crop-derived glucose and can meet the renewable-feedstock priority.
- Its slower, commonly batch operation may limit output compared with continuous hydration.
- Its aqueous product needs separation, and renewable crops still require land/resources.
Answer Fermentation fits the stated feedstock priority; slower output, separation and crop-resource needs remain trade-offs.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Give two advantages and two disadvantages of fermentation relative to the stated hydration comparison.
Give me a hint
Consider feedstock, reaction conditions, output rate and separation.
Compare my reasoning
- Advantages include renewable crop-derived glucose and lower reaction temperature without the stated high-pressure hydration operation.
- Disadvantages include comparatively slow, commonly batch processing and a dilute aqueous product requiring separation.
- Keep the claims comparative; low reaction temperature does not imply no total energy input.
Advantages: renewable glucose and low reaction temperature. Disadvantages: slower/batch production and separation of dilute aqueous ethanol.
Look for these in your work
- Both sides of the comparison are present.
- Reaction conditions and whole-process energy are distinguished.
A hypothetical plant already has ethene, high-pressure equipment and a priority for rapid continuous output. Choose a route and state two remaining disadvantages.
Give me a hint
Use the scenario rather than choosing solely by the word renewable.
Compare my reasoning
- Catalytic hydration fits the existing ethene supply and continuous-output priority.
- The required 300°C and 6000 kPa / 60 atm imply energy and equipment needs.
- If its ethene comes conventionally from petroleum, that feedstock is non-renewable; no universal purity or conversion guarantee follows.
Choose hydration for rapid continuous output; high-temperature/pressure requirements and conventional petroleum feedstock remain disadvantages.
Look for these in your work
- The choice uses the stated plant priorities.
- Two relevant disadvantages accompany the recommendation.
Supplied hypothetical process data give fermentation 30 energy units in reaction plus 90 in separation, and hydration 80 plus 20. Compare totals and assess the claim that fermentation must use less overall energy because its reaction is cooler.
Give me a hint
Add every supplied process step before comparing.
Compare my reasoning
- Fermentation totals 30+90=120 energy units.
- Hydration totals 80+20=100 energy units in this supplied model.
- Lower fermentation reaction temperature does not prove a lower total; here fermentation uses 20 more units. This is scenario data, not a universal industry measurement.
Fermentation 120 versus hydration 100 energy units; fermentation uses 20 more in this supplied scenario, despite its cooler reaction.
Look for these in your work
- Both totals use all supplied steps.
- The conclusion stays limited to the hypothetical data.
Common mistakes
- Saying renewable means zero resource use or automatically zero emissions.
- Calling fermentation fast and continuously identical to the stated hydration comparison.
- Claiming high-pressure hydration has no equipment or energy requirement.
- Treating reaction temperature alone as total process-energy demand.
What can you explain now?
Why can low-temperature fermentation still need substantial processing energy?
Compare with the explanation
Its dilute aqueous ethanol mixture needs separation and concentration.
The reaction temperature is only one part of the complete production process.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Compare both routes under four shared headings, then choose one for a new scenario while stating the disadvantage that your choice does not remove.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.