Cambridge IGCSE Chemistry · Syllabus 0620 · Organic Chemistry
Fermentation
What is Fermentation?
The process in which yeast converts aqueous glucose into ethanol and carbon dioxide, carried out at 25 to 35 degrees Celsius in the absence of oxygen.
This definition is part of the Organic Chemistry chapter in Cambridge IGCSE Chemistry.
Common mistakes with Fermentation
- “Air is bubbled through the fermentation mixture to keep the yeast alive.” Core 11.6.1 why it fails With oxygen present, the process is no longer fermentation, and any ethanol that does form can be oxidised further. correct Fermentation requires the absence of oxygen, with yeast, aqueous glucose and a temperature of 25–35 °C. Taught in 11.6.
- 11. “Air is bubbled through the fermentation mixture to keep the yeast alive.” Core 11.6.1 defect Oxygen introduced into a process defined by its absence. why Fermentation is what yeast does without oxygen. Admit oxygen and the process is no longer fermentation, so it no longer does the job the syllabus names it for. repair Add four words: “in the absence of oxygen”. transfer Write all four fermentation conditions in one sentence, with the oxygen condition named explicitly.
- 12. “Ethene is hydrated at 300 °C and 60 kPa.” Core 11.6.1 defect A unit error of a factor of 100. why 60 kPa is below atmospheric pressure. The answer describes a partial vacuum rather than a high-pressure plant. repair Write 6000 kPa, or write 60 atm. The number 60 belongs only with “atm”. transfer State both conditions for hydration and both for fermentation, with correct units throughout.