3.3.5 Alcohols for A-Level Chemistry (AQA)

What industrial process produces alcohols from alkenes?

Hydration

Steam adds across the C=C bond in the presence of an acid catalyst.

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What type of reaction converts an alkene into an alcohol using steam?

Electrophilic addition

The alkene double bond reacts with steam to form an alcohol.

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Fill in the blank:

In industrial hydration, alkenes react with _______ to produce alcohols.

steam

This reaction uses an acid catalyst such as phosphoric acid.

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True or False:

Ethanol can be produced biologically from glucose by fermentation.

True

Yeast enzymes convert glucose into ethanol and carbon dioxide.

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What microorganism is commonly used to ferment glucose to ethanol?

Yeast

Yeast contains enzymes that catalyse the fermentation reaction.

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Fill in the blank:

The fermentation of glucose produces ethanol and _______.

carbon dioxide

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

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True or False:

Fermentation occurs efficiently at temperatures around 30–40 °C.

True

Higher temperatures can kill the yeast enzymes.

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What process is used to separate ethanol from the fermentation mixture?

Fractional distillation

Ethanol is separated based on its boiling point.

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Fill in the blank:

A fuel produced from biological sources such as plants is called a _______ fuel.

biofuel

Biofuels are derived from renewable biological materials.

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Why is ethanol sometimes described as a carbon-neutral fuel?

Carbon cycle balance

CO₂ released during combustion equals CO₂ absorbed during plant growth.

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True or False:

Ethanol produced by fermentation is perfectly carbon neutral in practice.

False

Energy used in farming, processing and transport releases additional CO₂.

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Why must fermentation occur in the absence of oxygen?

Prevent oxidation

Oxygen would allow yeast to respire aerobically instead of producing ethanol.

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How are alcohols classified according to the carbon atom bonded to the –OH group?

Primary
Secondary
Tertiary

Classification depends on how many carbon atoms are attached to the carbon bearing the –OH group.

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What type of alcohol has the –OH group attached to a carbon bonded to only one other carbon?

Primary alcohol

Example: ethanol.

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Fill in the blank:

A secondary alcohol has the –OH group attached to a carbon bonded to _______ other carbons.

two

The central carbon is connected to two alkyl groups.

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True or False:

Tertiary alcohols are easily oxidised under normal laboratory conditions.

False

They resist oxidation because the –OH carbon lacks a hydrogen atom.

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What oxidising agent is commonly used to oxidise alcohols in the laboratory?

Acidified potassium dichromate

K₂Cr₂O₇ in acidic conditions is a common oxidising agent.

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True or False:

Primary alcohols can be oxidised first to aldehydes and then to carboxylic acids.

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True

Further oxidation occurs if strong oxidising conditions are used.

Fill in the blank:

Oxidation of a secondary alcohol produces a _______.

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ketone

The carbon–oxygen double bond forms at the alcohol carbon.

What determines whether a primary alcohol forms an aldehyde or a carboxylic acid during oxidation?

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Reaction conditions

Distillation forms aldehydes; reflux allows further oxidation to acids.

True or False:

Distillation is used during oxidation to collect aldehydes before they oxidise further.

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True

Aldehydes have lower boiling points and can be removed from the reaction mixture.

Fill in the blank:

The reagent that produces a silver mirror with aldehydes is _______ reagent.

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Tollens

Aldehydes reduce [Ag(NH₃)₂]⁺ to metallic silver.

What observation occurs when Fehling’s solution reacts with an aldehyde?

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Brick red precipitate

The aldehyde reduces Cu²⁺ to Cu₂O.

Why do ketones not react with Tollens’ reagent?

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Not easily oxidised

Ketones lack the hydrogen needed for oxidation under these conditions.

What type of **reaction** forms an **alkene from an alcohol** by removing water?

Elimination ## Footnote The alcohol loses H₂O to form a C=C double bond.

What **molecule** is removed from an **alcohol during elimination** to form an alkene?

Water ## Footnote The reaction is often called dehydration of an alcohol.

# Fill in the blank: **Acid-catalysed elimination** of alcohols produces _\_\_\_\_\_\_.

alkenes ## Footnote A double bond forms between adjacent carbon atoms.

# True or False: **Elimination of alcohols** requires an **acid catalyst**.

True ## Footnote Concentrated acids such as H₂SO₄ or H₃PO₄ are typically used.

What **role** does the **acid** play in the elimination of water from alcohols?

Catalyst ## Footnote It helps protonate the –OH group to make water a better leaving group.

# True or False: The **–OH group** in alcohols is converted into **water before leaving the molecule**.

True ## Footnote Protonation forms H₂O, which can leave more easily than OH^-.

# Fill in the blank: In the **elimination mechanism**, the alcohol is first _\_\_\_\_\_\_ to form a better leaving group.

protonated ## Footnote The –OH group gains a proton to become H₂O.

What **structural change** occurs in the molecule during **elimination of an alcohol**?

Double bond formation ## Footnote A C=C bond forms after removal of H₂O.

# True or False: **Alkenes produced from alcohols** can be used to make **addition polymers**.

True ## Footnote These alkenes can act as monomers in polymerisation reactions.

# Fill in the blank: The **elimination of water from alcohols** is also called _\_\_\_\_\_\_.

dehydration ## Footnote This term refers to removal of H₂O from the molecule.

What **laboratory technique** is used to purify **cyclohexene produced from cyclohexanol**?

Distillation ## Footnote The alkene is separated based on its boiling point.

Why is producing **alkenes from alcohols** environmentally beneficial compared with crude oil sources?

Renewable feedstocks ## Footnote Alcohols can be derived from biomass rather than fossil fuels.

What equation shows **CO₂ absorption during photosynthesis** (production of ethanol source)?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What equation shows **fermentation of glucose to produce ethanol**?

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

What equation shows **combustion of ethanol**?

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

What is the **general oxidation equation** for a **primary alcohol to an aldehyde**?

RCH₂OH + [O] → RCHO + H₂O

What is the **general oxidation equation** for an **aldehyde to a carboxylic acid**?

RCHO + [O] → RCOOH

What is the **oxidation equation for a secondary alcohol**?

R₁CHOHR₂ + [O] → R₁COR₂ + H₂O

What is the **overall oxidation equation** for a **primary alcohol to a carboxylic acid**?

RCH₂OH + 2[O] → RCOOH + H₂O

3.3.5 Alcohols Flashcards

Evaluate alcohol chemistry by predicting oxidation, substitution, and dehydration reactions using mechanisms. (43 cards)