Alcohols

Question 1

State the test to distinguish an alcohol from a carboxylic acid?

Answer 1

Add sodium hydrogen carbonate

Carboxylic acid: Effervescence
Alcohol: No reaction

Question 2

How is biofuel ethanol purified?

Answer 2

Using fractional distillation

Question 3

Why has direct hydration of ethene replaced the fermentation method?

Answer 3

The direct hydration does not require a catalyst

Question 4

Which compound is formed when 1-phenylethanol reacts with acidified potassium dichromate?

Answer 4

C6H5COCH3
(Phenyl group) + ( C=O ketone)

Question 5

How to test alcohol has been dehydrated into alkene?

Answer 5

Add bromine water
The solution will turn colourless if alkene is present

Question 6

Why is sodium carbonate added to the distillate in the dehydration of alcohols involving phosphoric acid?

Answer 6

To neutralise the phosphoric acid

Question 7

Give a property of anhydrous calcium chloride that allows it to act as a drying agent in dehydration of alcohols?

Answer 7

Anhydrous-absorbs water
Does not react with alkene

Question 8

Where is the OH group in a primary alcohol?

Answer 8

At the end of the chain

Question 9

Where is the OH group in a secondary alcohol?

Answer 9

In the body of the chain

Question 10

Where is the OH group in a tertiary alcohol?

Answer 10

At a branch in the chain

Question 11

How many R groups does a primary alcohol have?

Answer 11

1

Question 12

How many R groups does a secondary alcohol have ?

Answer 12

2

Question 13

How many R groups does a tertiary alcohol have?

Answer 13

3

Question 14

How are alcohols classified?

Answer 14

Primary, secondary, tertiary according to how many R groups are bonded to the carbon that has the OH group.

Question 15

Why are short chain alcohols soluble in water?

Answer 15

Soluble due to hydrogen bonding predominating

Question 16

Why are long chain alcohols insoluble in water?

Answer 16

Non-polar hydrocarbon chain dominates and so alcohol is insoluble in water.

Question 17

How is ethanol made by fermentation? (Reaction)

Answer 17

Glucose -> ethanol + carbon dioxide

Question 18

How is ethene produced at present?

Answer 18

Crude oil fractions are cracked , ethene is hydrated so water is added across the double bond

Question 19

Disadvantages of ethene production by fermentation

Answer 19

-slow rate of reaction
- aqueous solution of ethanol is produced rather than pure
- requires batches rather than continuous production

Question 20

Advantages of making ethene by carbohydrates (fermentation)

Answer 20

Renewable
Can be viewed as carbon neutral.

Question 21

Advantages of ethene production by crude oil?

Answer 21

Fast rate of reaction
Continuous process
Essentially pure product

Question 22

Disadvantages of ethene production by crude oil?

Answer 22

Non renewable - as crude oil is finite resource
Releases CO2

Question 23

General Equation for the complete combustion of alcohols ?

Answer 23

Alcohol + oxygen -> carbon dioxide and water

Question 24

What type of reaction are alcohols involved in?

Answer 24

Elimination reactions
Specifically Dehydration as water is lost

Question 25

Give two dehydrating agents for alcohols?

Answer 25

Phosphoric acid Sulfuric acid

Question 26

What can elimination reactions of longer or branched alcohols form?

Answer 26

Mixture of alkenes including E/Z isomers

Question 27

What are primary alcohols oxidised to?

Answer 27

Aldehydes ( C=O at the end and H at the end )

Question 28

What can aldehydes be oxidised to?

Answer 28

Carboxylic acids ( C=O bond at end and OH at the end )

Question 29

What are Secondary alcohols oxidised to?

Answer 29

Ketones ( C=O group within carbon chain)

Question 30

Can tertiary alcohols be oxidised and why?

Answer 30

Not easily oxidised Need C-C bond to break

Question 31

What solution is added to oxidise alcohols to aldehydes and ketones?

Answer 31

Potassium dichromate,acidified with dilute sulphuric acid

Question 32

What does potassium dichromate act as in the oxidising of alcohols ?

Answer 32

Oxidising agent

Question 33

What colour change is show in the oxidation of alcohols to aldehydes/ ketones

Answer 33

Orange to green

Question 34

Tests for aldehydes and ketones?

Answer 34

The tollens (silver mirror) test- silver nitrate in aqueous ammonia The fehlings test - blue copper solution

Question 35

Positive result for tollens with aldehyde ?

Answer 35

Silver mirror formed

Question 36

Positive result for fehlings with aldehyde?

Answer 36

Blue -> brick red precipitate

Question 37

Disadvantages of production of ethanol by fermentation?

Answer 37

Transport (petrol car engines would have to be modified to use fuels with high ethanol conc) This burns fuel that releases CO2 Extracting/ planting / harvesting which burns fuel that releases CO2

Question 38

Why can ethanol production by fermentation be deemed carbon neutral?

Answer 38

CO2 released when it is burnt is balanced by CO2 absorb by the plant

Question 39

Conditions of ethanol production by fermentation?

Answer 39

Anaerobic - used glucose 30-40 degrees Yeast - converts sugar into glucose

Question 40

Balanced reaction for industrial fermentation of glucose ?

Answer 40

C6H12O6 —> 2 C2H5OH + 2CO2