GCSE · Chemistry · Edexcel · Spec 1CH0

Fermentation production of ethanol

Picture a tiny factory that runs on sugar and gives you ethanol. That's yeast. But is it a good way to make ethanol? You'll be the judge.

You be the judge

Is fermentation a good way to make ethanol?

The claim

Fermentation is a good way to make ethanol.

Place each piece of evidence to load the balance. Mark the strong ones — they count double.

The glucose comes from crops, and more crops can be planted.
Evidence 1: does it support or challenge the claim?SupportsChallenges
Strong evidence
Growing the crops needs large areas of land.
Evidence 2: does it support or challenge the claim?SupportsChallenges
Strong evidence
Crops take in carbon dioxide by photosynthesis as they grow, which offsets the carbon dioxide released in fermentation.
Evidence 3: does it support or challenge the claim?SupportsChallenges
Strong evidence
The process is slow.
Evidence 4: does it support or challenge the claim?SupportsChallenges
Strong evidence
It is a batch process (made in separate stages rather than continually), and batch processes generally need cheaper equipment.
Evidence 5: does it support or challenge the claim?SupportsChallenges
Strong evidence
The product is impure, so it then has to be purified.
Evidence 6: does it support or challenge the claim?SupportsChallenges
Strong evidence

Meet the product

Tap each molecule. Ethanol is the one with the most to say.

Tap a molecule to see what it does in the reaction.

Which one sounds like you?

What does fermentation need?

You're setting up a fermentation to turn glucose from crops into ethanol.

Which of these is closest to what you think right now?

It needs oxygen, a bit like breathing does.It needs glucose from crops, yeast, about 30 °C and no oxygen.The hotter you keep it, the better it works.Glucose and the right temperature are enough. It just happens.

How sure are you?

I'm sureI think soI'm guessing

It needs oxygen, a bit like breathing does.

This is a common misconception

Easy to assume, but it's the other way round. Fermentation is the anaerobic respiration of microorganisms, and anaerobic means without oxygen. So oxygen isn't one of the conditions.

It needs glucose from crops, yeast, about 30 °C and no oxygen.

This matches the evidence

That's all four. Glucose from crops is what gets converted, yeast is the microorganisms doing the respiration, about 30 °C is the warm temperature, and anaerobic means without oxygen.

The hotter you keep it, the better it works.

This is a common misconception

Tempting, but the condition is a warm temperature of about 30 °C. That is the figure to remember. Nothing in the conditions says 'as hot as you can get it'.

Glucose and the right temperature are enough. It just happens.

This is a common misconception

Something is missing: the microorganisms. Fermentation results from the anaerobic respiration of microorganisms, and here they are yeast. Yeast is one of the conditions.

Four conditions: glucose from crops, yeast, about 30 °C, and anaerobic conditions, which means without oxygen.

Chemistry · Reaction balancer

Balance the fermentation equation

Tap + or − under a molecule to change the big number in front of it. Keep going until every element matches on both sides.

Reactants

C₆H₁₂O₆

Products

C₂H₅OH

CO₂

C6→3✗

H12→6✗

O6→3✗

Conservation check: count atoms on both sides.Not yet.

When every tally matches, the equation is balanced. Glucose in, two ethanol and two carbon dioxide out.

Tap + or − under each molecule to set its coefficient.

Exam line: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Watch out: Count the hydrogen in C₂H₅OH carefully: five in C₂H₅ plus the one in the -OH makes six hydrogen atoms in each ethanol molecule.

Why 'carbon neutral'?

Rebuild the carbon loop

2 stages are missing. Use the rest of the loop to work out which goes where.

Stage 1: Carbon dioxide in the atmosphere
Where the loop starts.
Stage 3: Glucose from the crops
The sugar that gets fermented.
Stage 5: Carbon dioxide is released
Released carbon dioxide goes back to the atmosphere.

…and stage 5 leads back to stage 1.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What you need to know

Alcohols are a homologous series containing the -OH functional group, and ethanol has two carbon atoms.
Fermentation makes solutions of ethanol from sugars, using the anaerobic respiration of microorganisms.
Conditions: glucose from crops, yeast, a warm temperature of about 30 °C, and anaerobic conditions.
Anaerobic means without oxygen.
Have a goMaya says: "Glucose plus yeast is plenty. The rest is just fussiness." Which two conditions is she leaving out?
About 30 °C, and anaerobic conditions (no oxygen).
All four conditions go together: glucose from crops, yeast, about 30 °C and anaerobic conditions.
Glucose is converted into ethanol and carbon dioxide: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
Have a goA tub holds 10 molecules of glucose, and every one is fermented. How many ethanol and how many carbon dioxide molecules do you end up with?
20 ethanol and 20 carbon dioxide molecules.
Each glucose molecule makes two ethanol and two carbon dioxide, so you double the glucose count for each product.
Advantages: renewable glucose (more crops can be planted), considered carbon neutral, and a batch process that generally needs cheaper equipment.
Disadvantages: it needs large areas of land, it's slow, and the impure product has to be purified.
Ethanol goes into alcoholic drinks like wine and beer, and into fuel: E10 petrol contains up to 10% renewable ethanol.
Have a goA 50-litre tank is full of E10 petrol. Treating the 10% as a share of the fuel, what is the most ethanol it could contain?
5 litres.
E10 contains up to 10% renewable ethanol, so 10% of 50 litres is the ceiling, not a fixed amount.
Ethanol is a solvent too, but that's a property of short-chain alcohols in general, not of fermentation ethanol.

The big picture

Yeast ferments glucose from crops into ethanol and carbon dioxide at about 30 °C with no oxygen. The method is renewable and considered carbon neutral, but it needs lots of land, is slow and gives an impure product.

Key points

1Fermentation needs glucose from crops, yeast, about 30 °C and anaerobic conditions (without oxygen).

2One glucose molecule gives two ethanol molecules and two carbon dioxide molecules.

3For: renewable glucose, considered carbon neutral, batch process with generally cheaper equipment.

4Against: large areas of land, slow, impure product that must be purified.

5Ethanol is an alcohol with the -OH group: structural formula CH₃CH₂OH (C₂H₅OH), molecular formula C₂H₆O.

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Worked example

Problem

Show that oxygen balances in C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ by counting the oxygen atoms on each side.

⚠ Watch out

Two traps. First, 'carbon neutral' does not mean no carbon dioxide is released: fermentation does release it (two molecules per glucose), and it is considered offset by what the crops took in. Second, fermentation is anaerobic, so it does not need oxygen.

🧠

Memory hook

Borrow and return: the crops borrow carbon dioxide from the air as they grow, and fermentation gives it back. That's why the process is considered carbon neutral.

✓

Check yourself

Zara says: "Fermentation releases carbon dioxide, so it can't be carbon neutral." Write a two-sentence reply that uses the crops, then name one disadvantage that stops fermentation being a perfect method.

Flashcards

(13)

What functional group makes ethanol an alcohol?

The -OH group. Alcohols are a homologous series of compounds containing -OH.

Ethanol: structural formula vs molecular formula?

Structural: CH₃CH₂OH (written C₂H₅OH). Molecular: C₂H₆O.

What is fermentation?

A process that makes solutions of ethanol from sugars, resulting from the anaerobic respiration of microorganisms.

Name the four conditions for fermentation.

Glucose from crops, yeast, a warm temperature of about 30 °C, and anaerobic conditions.

What does anaerobic mean?

Without oxygen.

Word equation and symbol equation for fermentation?

glucose → ethanol + carbon dioxide C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

What is a batch process, and what does it generally allow?

One made in separate stages rather than continually. Batch processes generally need cheaper equipment.

Why is the glucose for fermentation called a renewable source?

It comes from crops, and more crops can be planted.

Give three advantages of making ethanol by fermentation.

Renewable glucose; considered carbon neutral; a batch process with generally cheaper equipment.

Give three disadvantages of making ethanol by fermentation.

It needs large areas of land; it is slow; the product is impure and has to be purified.

What does 'considered' carbon neutral leave out?

It is the simplified view. It ignores energy used in farming, transport, fermentation and purification.

What does E10 petrol contain?

Up to 10% renewable ethanol, not a fixed 10%.

Name three uses of ethanol.

Alcoholic drinks such as wine and beer; fuel; solvent.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Is fermentation a good way to make ethanol?

What does fermentation need?

Balance the fermentation equation

Rebuild the carbon loop

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