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Chemistry Alevel - Module 4 > 4.1.4 - Alcohols > Flashcards

4.1.4 - Alcohols Flashcards

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1
Q

What is an alcohol?

A

An alcohol is an organic molecule with a hydroxyl functional group (-OH).

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2
Q

Why do alcohols have relatively low volatility?

A

Because they can form hydrogen bonds between alcohol molecules.

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3
Q

Why does solubility of alcohols decrease as the carbon chain length increases?

A

Because the hydrocarbon part becomes more significant, reducing the alcohol’s ability to form hydrogen bonds with water.

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3
Q

What is a primary alcohol?

A

An alcohol where the carbon attached to the OH group is bonded to one other carbon.

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3
Q

What reagent is used to oxidise alcohols?

A

Potassium dichromate (K₂Cr₂O₇) and dilute sulfuric acid.

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3
Q

What is the general formula for alcohols?

A

CnH2n+1OH

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4
Q

What is a secondary alcohol?

A

An alcohol where the carbon attached to the OH group is bonded to two other carbons.

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4
Q

What is ethanol used for?

A

Alcoholic drinks and as a solvent (in methylated spirits).

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4
Q

Why are small alcohols soluble in water?

A

They can form hydrogen bonds with water molecules.

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4
Q

What is methanol used for?

A

As a petrol additive to improve combustion and as a feedstock in organic synthesis.

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4
Q

What are the products of complete combustion of alcohols?

A

Carbon dioxide (CO₂) and water (H₂O).

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4
Q

What is a tertiary alcohol?

A

An alcohol where the carbon attached to the OH group is bonded to three other carbons.

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4
Q

What are the conditions for complete combustion?

A

Excess oxygen.

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4
Q

What is the product of partial oxidation of a primary alcohol?

A

An aldehyde.

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4
Q

What are the conditions required for the partial oxidation of a primary alcohol?

A

Limited K₂Cr₂O₇, warm gently, distil out the aldehyde as it forms. Acidify using sulfuric acid.

Primary Alcohol + [O] –> Aldehyde + H2O

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5
Q

What is the colour change when potassium dichromate is reduced?

A

Orange → Green (due to Cr³⁺ ions).

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5
Q

What is the functional group of an aldehyde? How do you name an aldehyde?

A

Orange chicken read hungry
-al
Ethanal

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5
Q

Why is distillation used in the partial oxidation of a primary alcohol?

A

To separate and collect the aldehyde before it oxidises further.

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6
Q

Draw the distillation diagram.

A
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6
Q

Why does water enter the bottom of the condenser?

A

To ensure efficient cooling and prevent backflow.

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6
Q

Why should the thermometer bulb be at the T-junction in distillation?

A

To accurately measure the temperature of the vapour entering the condenser.

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6
Q

Why are electric heaters used in organic reactions?

A

Because organic compounds are flammable and could ignite with a naked flame.

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6
Q

Why cool the collection flask in ice?

A

To increase the yield of the distillate.

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6
Q

What is the functional group of a carboxylic acid? How do you name a carboxylic acid?

A

COOH
-oic acid
Methanoic acid

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6
What is the product of full oxidation of a primary alcohol?
A carboxylic acid.
6
Draw the reflux diagram.
6
What are the conditions required for the full oxidation of a primary alcohol?
Excess K₂Cr₂O₇, heat under reflux. Acidify using sulfuric acid Primary Alcohol + [O] --> Carboxylic acid + H2O
6
What does a reflux condenser do?
Condenses vapours and returns them to the reaction flask.
6
Why use reflux to fully oxidise a primary alcohol?
To heat the reaction for long periods without losing volatile organic vapours.
6
Why must the end of a condenser be open in reflux?
To prevent pressure build-up, which could cause an explosion.
6
Why are anti-bumping granules used?
To ensure smooth boiling and prevent violent bubbling.
6
What is the product of oxidising a secondary alcohol?
A ketone.
6
What is the functional group of a ketone? How do you name a ketone?
OCRR -one Propanone
6
What are the conditions required for the oxidation of a secondary alcohol?
K₂Cr₂O₇, dilute H₂SO₄, heat under reflux. Secondat Alcohol + [O] --> Ketone + H2O
6
What does dehydration mean?
The removal of a water molecule from a compound.
6
Do ketones require numbering in their names?
Yes, if the carbon chain has 5 or more carbons.
6
What is the suffix for naming ketones?
-one
6
Can ketones be further oxidised under these conditions?
No — ketones are resistant to further oxidation with dichromate.
6
What is the product of dehydration of an alcohol?
An alkene. Alcohol --> Concentrated H2SO4 + Reflux --> Alkene + H2O
6
What is the product of substituting an alcohol with a halide?
A haloalkane.
7
What reagents are needed for the dehydration of an alcohol?
Concentrated sulfuric acid or phosphoric acid.
7
What are the conditions needed for the dehydration of an alcohol?
Warm under reflux.
7
Can tertiary alcohols be oxidised by potassium dichromate?
No — there is no hydrogen attached to the carbon bearing the OH group.
7
What is the role of the acid in the dehydration of an alcohol?
It acts as a dehydrating agent and catalyst.
7
What type of reaction is the dehydration of an alcohol?
Acid-catalysed elimination.
7
How do alcohols react to form haloalkanes?
They react with hydrogen halides (e.g. HBr) via a substitution reaction.
7
What is the functional group of a haloalkane? How do you name an haloalkane?
R--X Halo- Chloroethane
7
What type of reaction is the substitution of an alcohol with a halide?
Nucleophilic substitution.
7
What reagents are used in the substitution of an alcohol with a halide?
A mixture of a sodium halide (e.g., NaCl) and concentrated sulfuric acid.
7
How is the hydrogen halide (e.g. HBr) generated in situ?
By reacting a sodium halide (e.g. NaBr) with concentrated sulfuric acid.
7
Write the equation for the formation of HBr from NaBr and H₂SO₄.
H₂SO₄ + NaBr → NaHSO₄ + HBr
7
What is the reaction between ethanol and HBr?
CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O
7
What is the overall equation when making a haloalkane from alcohol using NaBr and H₂SO₄?
CH₃CH₂OH + H₂SO₄ + NaBr → CH₃CH₂Br + NaHSO₄ + H₂O
7
What does low volatility mean in terms of boiling point?
Low volatility = high boiling point.
7
Do alcohols have higher or lower volatility than alkanes and alkenes?
Lower volatility (i.e. higher boiling points).
8
Why do alcohols have higher boiling points than alkanes and alkenes?
Because alcohols form hydrogen bonds between molecules, which are stronger than the London dispersion forces in alkanes and alkenes.
9
What two types of intermolecular forces are present in alcohols?
London dispersion forces and hydrogen bonding.
10
Why do alcohols have stronger London forces than alkenes/alkanes?
Because they are larger molecules with more electrons.
10
Why do hydrogen bonds raise the boiling point of alcohols?
Because they are strong intermolecular forces that require more energy to break.
11
Why are alcohols more soluble in water than alkanes or alkenes?
Because the –OH group can form hydrogen bonds with polar water molecules.
12
Why do alcohols become less soluble as their carbon chain length increases?
Because the non-polar hydrocarbon chain becomes larger, weakening the attraction between the alcohol and water.
12
Does the carbon chain form strong interactions with water?
No — it is non-polar and doesn’t form strong attractions with polar water molecules.
12
How can you test for the presence of an –OH group in an alcohol?
By reacting it with phosphorus(V) chloride (PCl₅); steamy white fumes of HCl gas are produced.
12
What is the visible result when PCl₅ is added to an alcohol?
Steamy white fumes of hydrogen chloride gas are observed.
13
Why is PCl₅ used as a test for alcohols?
Because it reacts rapidly with the –OH group to produce HCl gas, confirming the presence of an alcohol.
13
Write a general equation for the reaction of an alcohol with PCl₅.
ROH + PCl₅ → RCl + POCl₃ + HCl
14
What are the advantages of using SOCl₂ (thionyl chloride) to convert alcohols to halo alkanes?
The by-products (SO₂ and HCl) are gases and escape, making product purification easier.
15
What makes SOCl₂ a convenient reagent in organic synthesis?
It produces gaseous by-products, simplifying the isolation of the desired haloalkane.
15
Write the general reaction of an alcohol with SOCl₂ (thionyl chloride).
ROH + SOCl₂ → RCl + SO₂ + HCl
15
What are three different reagents that can be used to convert an alcohol to a chloroalkane?
1. NaCl + H₂SO₄ (in situ HCl), 2. PCl₅, 3. SOCl₂

Chemistry Alevel - Module 4 (5 decks)

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