An alcohol is a compound containing at least one hydroxy (-OH) functional group, with general formula C n H 2n+1 OH.

What reagents and conditions are needed to produce an alcohol by electrophilic addition of an alkene?

Steam is reacted with an alkene using concentrated phosphoric(V) acid (H 3 PO 4 ) as a catalyst and heat.

True or False? Cold, dilute KMnO 4 oxidises an alkene to form a diol without fully breaking the C=C bond.

True. Cold, dilute KMnO 4 is a mild oxidising agent. It oxidises the alkene so that both carbons of the double bond gain an -OH group, forming a diol.

Halogenoalkanes can be converted to alcohols by heating with .......... . This is a .......... substitution reaction.

Halogenoalkanes can be converted to alcohols by heating with aqueous NaOH . This is a nucleophilic substitution reaction.

What type of alcohol is formed when an aldehyde is reduced, and what reducing agents can be used?

Aldehydes are reduced to primary alcohols . Suitable reducing agents are NaBH 4 or LiAlH 4 .

True or False? NaBH 4 is a strong enough reducing agent to reduce a carboxylic acid to a primary alcohol.

False. NaBH 4 is not strong enough to reduce carboxylic acids. LiAlH 4 must be used instead.

Hydrolysis of an ester with dilute acid or alkali and heat reforms a .......... and an .......... .

Hydrolysis of an ester with dilute acid or alkali and heat reforms a carboxylic acid and an alcohol .

A diol is a compound containing two hydroxy (-OH) groups, formed when an alkene is oxidised by cold, dilute KMnO 4 .

Which reaction type converts a ketone into a secondary alcohol, and which reducing agents are used?

Reduction converts a ketone into a secondary alcohol . Both NaBH 4 and LiAlH 4 can be used as reducing agents.

Define esterification .

An esterification is a condensation reaction between a carboxylic acid and an alcohol, producing an ester and water, using a strong acid catalyst such as H 2 SO 4 .

What products are formed when ethanol undergoes complete combustion?

Complete combustion of ethanol produces carbon dioxide and water . C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O

True or False? Tertiary alcohols are oxidised to ketones when treated with acidified K 2 Cr 2 O 7 .

False. Tertiary alcohols do not undergo oxidation with acidified K 2 Cr 2 O 7 . Only primary and secondary alcohols can be oxidised.

When a primary alcohol is oxidised and the product is distilled off immediately, a .......... is formed. If refluxed with excess oxidising agent, a .......... is formed instead.

When a primary alcohol is oxidised and the product is distilled off immediately, an aldehyde is formed. If refluxed with excess oxidising agent, a carboxylic acid is formed instead.

What colour change is observed when an alcohol is oxidised by acidified potassium dichromate(VI)?

The solution changes from orange to green . The orange Cr 2 O 7 2- ions are reduced to green Cr 3+ ions.

True or False? Dehydration of an alcohol is a type of elimination reaction that produces an alkene.

True. Dehydration removes a water molecule from the alcohol. It is an elimination reaction, producing an alkene. A hot catalyst such as Al 2 O 3 is used.

An alkoxide is the basic salt formed when an alcohol reacts with a reactive metal such as sodium, with hydrogen gas also produced.

Alcohols can be converted to halogenoalkanes by reaction with .......... , PCl 3 , PCl 5 or SOCl 2 in a .......... substitution reaction.

Alcohols can be converted to halogenoalkanes by reaction with HX , PCl 3 , PCl 5 or SOCl 2 in a substitution reaction.

What product is formed when a secondary alcohol is oxidised, and does it require immediate distillation?

A secondary alcohol is oxidised to a ketone . Ketones cannot be further oxidised, so immediate distillation is not required.

Define primary alcohol .

A primary alcohol is an alcohol in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group).

How can acidified K 2 Cr 2 O 7 be used to distinguish between primary, secondary and tertiary alcohols?

Primary and secondary alcohols both turn the orange solution green (they are oxidised). Tertiary alcohols give no colour change as they cannot be oxidised.

True or False? A tertiary alcohol has its -OH group attached to a carbon bonded to three other carbon atoms.

True. In a tertiary alcohol the carbon bearing the -OH group is bonded to three other carbon (alkyl) groups.

The iodoform test uses iodine in .......... solution. A positive result gives a yellow precipitate of .......... .

The iodoform test uses iodine in alkaline solution. A positive result gives a yellow precipitate of CHI 3 .

Which two classes of compound give a positive iodoform test, and what structural feature do they share?

Methyl ketones (compounds with a CH 3 CO- group) and ethanal both give a positive iodoform test. They both contain the CH 3 CO- group.

True or False? Butan-2-ol gives a positive iodoform test because it can be oxidised to a methyl ketone.

True. Butan-2-ol has the structure CH 3 CH(OH)R, so alkaline iodine first oxidises it to butanone (a methyl ketone), which then undergoes halogenation and hydrolysis to give a yellow CHI 3 precipitate.

Define secondary alcohol .

A secondary alcohol is an alcohol in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups).

In the iodoform reaction, the .......... step replaces all three H atoms of the -CH 3 group with iodine. The .......... step then forms CHI 3 and a sodium carboxylate salt.

In the iodoform reaction, the halogenation step replaces all three H atoms of the -CH 3 group with iodine. The hydrolysis step then forms CHI 3 and a sodium carboxylate salt.

Why does a tertiary alcohol not change the colour of acidified K 2 Cr 2 O 7 ?

A tertiary alcohol cannot be oxidised because the carbon bearing the -OH group has no hydrogen atom attached to it. Without a C-H bond at that carbon, oxidation cannot occur, so the orange colour of Cr 2 O 7 2- is unchanged .

Define positive inductive effect .

A positive inductive effect is the donation of electron density into a covalent bond by an electron-donating group such as an alkyl group.

Are alcohols stronger or weaker acids than water? Give a reason.

Alcohols are weaker acids than water. The alkyl group in the alkoxide ion donates electron density to the oxygen, making it more likely to re-accept a proton and reform the alcohol, so [H + (aq)] is lower than in water.

True or False? Alcohols dissociate to a greater extent than water when dissolved in solution.

False. Alcohols have a low degree of dissociation. The equilibrium ROH ⇌ RO - + H + lies far to the left, giving a lower [H + ] than water.

In the dissociation equilibrium ROH ⇌ RO - + H + , the position of equilibrium lies to the .......... , meaning there are far more .......... molecules than ions.

In the dissociation equilibrium ROH ⇌ RO - + H + , the position of equilibrium lies to the left , meaning there are far more alcohol molecules than ions.

Why does the alkoxide ion (RO - ) tend to re-accept a proton more readily than the hydroxide ion (OH - )?

The alkoxide ion has an electron-donating alkyl group attached to the oxygen. This increases electron density on the O - atom, making it more likely to attract and accept a proton. The hydroxide ion has no such alkyl group, so its oxygen is less electron-rich.

True or False? The longer the hydrocarbon chain in an alcohol, the stronger the positive inductive effect and the weaker the acid.

True. Longer alkyl chains have a greater positive inductive effect, donating more electron density to the O - atom of the alkoxide ion, increasing its tendency to re-accept a proton and reducing the acidity further.

Define alkoxide ion .

An alkoxide ion is the negatively charged ion (RO - ) formed when an alcohol loses a proton from its -OH group.

Alcohols are .......... acids because the alkyl group in the alkoxide ion has a .......... inductive effect, making the O - more likely to re-accept a proton.

Alcohols are weaker acids because the alkyl group in the alkoxide ion has a positive inductive effect, making the O - more likely to re-accept a proton.

What happens to the position of the equilibrium when water dissociates compared to when an alcohol dissociates?

In both cases the equilibrium lies to the left, but water dissociates to a greater extent than alcohols. Water therefore produces a higher [H + (aq)] , making it a stronger acid than alcohols.

A LevelChemistryCambridge (CIE)Flashcards16. Hydroxy CompoundsAlcohols

Alcohols (Cambridge (CIE) A Level Chemistry): Flashcards

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Cards in this collection (36)

Define alcohol.
An alcohol is a compound containing at least one hydroxy (-OH) functional group, with general formula C_nH_2n+1OH.
What reagents and conditions are needed to produce an alcohol by electrophilic addition of an alkene?
Steam is reacted with an alkene using concentrated phosphoric(V) acid (H₃PO₄) as a catalyst and heat.
True or False?
Cold, dilute KMnO₄ oxidises an alkene to form a diol without fully breaking the C=C bond.
True.
Cold, dilute KMnO₄ is a mild oxidising agent. It oxidises the alkene so that both carbons of the double bond gain an -OH group, forming a diol.
Halogenoalkanes can be converted to alcohols by heating with .......... . This is a .......... substitution reaction.
Halogenoalkanes can be converted to alcohols by heating with aqueous NaOH. This is a nucleophilic substitution reaction.
What type of alcohol is formed when an aldehyde is reduced, and what reducing agents can be used?
Aldehydes are reduced to primary alcohols. Suitable reducing agents are NaBH₄ or LiAlH₄.
True or False?
NaBH₄ is a strong enough reducing agent to reduce a carboxylic acid to a primary alcohol.
False.
NaBH₄ is not strong enough to reduce carboxylic acids. LiAlH₄ must be used instead.
Hydrolysis of an ester with dilute acid or alkali and heat reforms a .......... and an .......... .
Hydrolysis of an ester with dilute acid or alkali and heat reforms a carboxylic acid and an alcohol.
What is a diol?
A diol is a compound containing two hydroxy (-OH) groups, formed when an alkene is oxidised by cold, dilute KMnO₄.
Which reaction type converts a ketone into a secondary alcohol, and which reducing agents are used?
Reduction converts a ketone into a secondary alcohol. Both NaBH₄ and LiAlH₄ can be used as reducing agents.
Define esterification.
An esterification is a condensation reaction between a carboxylic acid and an alcohol, producing an ester and water, using a strong acid catalyst such as H₂SO₄.
What products are formed when ethanol undergoes complete combustion?
Complete combustion of ethanol produces carbon dioxide and water.
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
True or False?
Tertiary alcohols are oxidised to ketones when treated with acidified K₂Cr₂O₇.
False.
Tertiary alcohols do not undergo oxidation with acidified K₂Cr₂O₇. Only primary and secondary alcohols can be oxidised.
When a primary alcohol is oxidised and the product is distilled off immediately, a .......... is formed. If refluxed with excess oxidising agent, a .......... is formed instead.
When a primary alcohol is oxidised and the product is distilled off immediately, an aldehyde is formed. If refluxed with excess oxidising agent, a carboxylic acid is formed instead.
What colour change is observed when an alcohol is oxidised by acidified potassium dichromate(VI)?
The solution changes from orange to green. The orange Cr₂O₇^2- ions are reduced to green Cr³⁺ ions.
True or False?
Dehydration of an alcohol is a type of elimination reaction that produces an alkene.
True.
Dehydration removes a water molecule from the alcohol. It is an elimination reaction, producing an alkene. A hot catalyst such as Al₂O₃ is used.
Define alkoxide.
An alkoxide is the basic salt formed when an alcohol reacts with a reactive metal such as sodium, with hydrogen gas also produced.
Alcohols can be converted to halogenoalkanes by reaction with .........., PCl₃, PCl₅ or SOCl₂ in a .......... substitution reaction.
Alcohols can be converted to halogenoalkanes by reaction with HX, PCl₃, PCl₅ or SOCl₂ in a substitution reaction.
What product is formed when a secondary alcohol is oxidised, and does it require immediate distillation?
A secondary alcohol is oxidised to a ketone. Ketones cannot be further oxidised, so immediate distillation is not required.
Define primary alcohol.
A primary alcohol is an alcohol in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group).
How can acidified K₂Cr₂O₇ be used to distinguish between primary, secondary and tertiary alcohols?
Primary and secondary alcohols both turn the orange solution green (they are oxidised). Tertiary alcohols give no colour change as they cannot be oxidised.
True or False?
A tertiary alcohol has its -OH group attached to a carbon bonded to three other carbon atoms.
True.
In a tertiary alcohol the carbon bearing the -OH group is bonded to three other carbon (alkyl) groups.
The iodoform test uses iodine in .......... solution. A positive result gives a yellow precipitate of ...........
The iodoform test uses iodine in alkaline solution. A positive result gives a yellow precipitate of CHI₃.
Which two classes of compound give a positive iodoform test, and what structural feature do they share?
Methyl ketones (compounds with a CH₃CO- group) and ethanal both give a positive iodoform test. They both contain the CH₃CO- group.
True or False?
Butan-2-ol gives a positive iodoform test because it can be oxidised to a methyl ketone.
True.
Butan-2-ol has the structure CH₃CH(OH)R, so alkaline iodine first oxidises it to butanone (a methyl ketone), which then undergoes halogenation and hydrolysis to give a yellow CHI₃ precipitate.
Define secondary alcohol.
A secondary alcohol is an alcohol in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups).
In the iodoform reaction, the .......... step replaces all three H atoms of the -CH₃ group with iodine. The .......... step then forms CHI₃ and a sodium carboxylate salt.
In the iodoform reaction, the halogenation step replaces all three H atoms of the -CH₃ group with iodine. The hydrolysis step then forms CHI₃ and a sodium carboxylate salt.
Why does a tertiary alcohol not change the colour of acidified K₂Cr₂O₇?
A tertiary alcohol cannot be oxidised because the carbon bearing the -OH group has no hydrogen atom attached to it. Without a C-H bond at that carbon, oxidation cannot occur, so the orange colour of Cr₂O₇^2- is unchanged.
Define positive inductive effect.
A positive inductive effect is the donation of electron density into a covalent bond by an electron-donating group such as an alkyl group.
Are alcohols stronger or weaker acids than water? Give a reason.
Alcohols are weaker acids than water. The alkyl group in the alkoxide ion donates electron density to the oxygen, making it more likely to re-accept a proton and reform the alcohol, so [H⁺(aq)] is lower than in water.
True or False?
Alcohols dissociate to a greater extent than water when dissolved in solution.
False.
Alcohols have a low degree of dissociation. The equilibrium ROH ⇌ RO^- + H⁺ lies far to the left, giving a lower [H⁺] than water.
In the dissociation equilibrium ROH ⇌ RO^- + H⁺, the position of equilibrium lies to the .........., meaning there are far more .......... molecules than ions.
In the dissociation equilibrium ROH ⇌ RO^- + H⁺, the position of equilibrium lies to the left, meaning there are far more alcohol molecules than ions.
Why does the alkoxide ion (RO^-) tend to re-accept a proton more readily than the hydroxide ion (OH^-)?
The alkoxide ion has an electron-donating alkyl group attached to the oxygen. This increases electron density on the O^- atom, making it more likely to attract and accept a proton. The hydroxide ion has no such alkyl group, so its oxygen is less electron-rich.
True or False?
The longer the hydrocarbon chain in an alcohol, the stronger the positive inductive effect and the weaker the acid.
True.
Longer alkyl chains have a greater positive inductive effect, donating more electron density to the O^- atom of the alkoxide ion, increasing its tendency to re-accept a proton and reducing the acidity further.
Define alkoxide ion.
An alkoxide ion is the negatively charged ion (RO^-) formed when an alcohol loses a proton from its -OH group.
Alcohols are .......... acids because the alkyl group in the alkoxide ion has a .......... inductive effect, making the O^- more likely to re-accept a proton.
Alcohols are weaker acids because the alkyl group in the alkoxide ion has a positive inductive effect, making the O^- more likely to re-accept a proton.
What happens to the position of the equilibrium when water dissociates compared to when an alcohol dissociates?
In both cases the equilibrium lies to the left, but water dissociates to a greater extent than alcohols. Water therefore produces a higher [H⁺(aq)], making it a stronger acid than alcohols.

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