Write the equation for hydration of ethene.

CH₂=CH₂ + H₂O → CH₃CH₂OH

What is the first step in the mechanism of hydration of ethene?

The C=C electrons attack H⁺, forming a C–H bond and the carbocation CH₃CH₂⁺.

What is the role of water in the hydration mechanism?

A lone pair on its oxygen attacks the carbocation, so it acts as a nucleophile.

Write the equation for fermentation of glucose.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

List the conditions for fermentation.

Yeast, about 35 °C, aqueous solution, no air.

Why is fermentation not carried out at high temperature?

The enzymes in yeast would denature.

Why is air excluded from fermentation?

Oxygen would oxidise the ethanol to ethanoic acid.

A fuel made from biological material, such as plants.

Why is ethanol from fermentation said to be carbon neutral?

The CO₂ released equals the CO₂ absorbed by the crop in photosynthesis.

Why is the carbon neutral claim not valid?

Fossil fuels are used for farming, fertiliser, transport and distillation, so CO₂ is released.

Give an ethical issue with biofuels.

Farmland used for fuel crops cannot grow food, which may raise food prices.

Alcohol productionAQA A-Level Chemistry: Flashcards

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How are alcohols made industrially from alkenes?

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How are alcohols made industrially from alkenes?: By hydration with steam in the presence of an acid catalyst.
Write the equation for hydration of ethene.: CH₂=CH₂ + H₂O → CH₃CH₂OH
What is the first step in the mechanism of hydration of ethene?: The C=C electrons attack H⁺, forming a C–H bond and the carbocation CH₃CH₂⁺.
What is the role of water in the hydration mechanism?: A lone pair on its oxygen attacks the carbocation, so it acts as a nucleophile.
Write the equation for fermentation of glucose.: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
List the conditions for fermentation.: Yeast, about 35 °C, aqueous solution, no air.
Why is fermentation not carried out at high temperature?: The enzymes in yeast would denature.
Why is air excluded from fermentation?: Oxygen would oxidise the ethanol to ethanoic acid.
How is ethanol separated from the fermentation mixture?: Fractional distillation.
What is a biofuel?: A fuel made from biological material, such as plants.
Why is ethanol from fermentation said to be carbon neutral?: The CO₂ released equals the CO₂ absorbed by the crop in photosynthesis.
Why is the carbon neutral claim not valid?: Fossil fuels are used for farming, fertiliser, transport and distillation, so CO₂ is released.
Give an ethical issue with biofuels.: Farmland used for fuel crops cannot grow food, which may raise food prices.

Exam questions on Alcohol production

Ethanol is manufactured industrially in two ways: by the hydration of ethene using steam and an acid catalyst, and by the fermentation of glucose using yeast. The ethanol from fermentation is present in a dilute mixture with water and other substances.
Write an equation for the fermentation of glucose to ethanol.2 marks
Bioethanol made from sugar cane is blended with petrol in some countries. Supporters of this fuel describe it as carbon neutral, so a student investigates the processes involved.
Write an equation for the photosynthesis that forms glucose and an equation for the complete combustion of ethanol.2 marks
A plant manager is comparing two routes to ethanol: fermentation of glucose by yeast, and the acid-catalysed hydration of ethene by steam. The staff must understand the conditions for the first route and the mechanism of the second.
Justify the conditions used for the fermentation of glucose: yeast, a temperature of about 35 °C, and the absence of air.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).