3.5 - Alcohol

Question 1

What is the bonding between alcohols molecules?

Answer 1

Hydrogen bonding

Question 2

General alcohol formula

Answer 2

CnH2n+1OH

Question 3

The longer the hydrocarbon chain becomes, what happens to solubility?

Answer 3

The longer hydrocarbon chain, the less soluble the alcohol.

Question 4

Uses of ethanol

Answer 4

1. Commonly used as a solvent in form of methylated spirit

Question 5

Use of methanol

Answer 5

1. Used as a petrol additive to improve combustion

Question 6

Describe partial oxidation of primary alcohol

Answer 6

Produces aldehyde
Reagent - potassium dichromate and dilute sulfuric acid
Use limited amount of dichromate

Distill condition - warm gently and distill as it forms

Question 7

Observation for partial oxidation of primary alcohol

Answer 7

Orange to green colour change

Question 8

What is the product of complete oxidation of primary alcohol

Answer 8

Carboxylic acid

Question 9

Reagent of full oxidation of primary alcohol

Answer 9

Potassium dichromate and dilute sulphuric acid

Question 10

Conditions of complete oxidation of 1o alcohol.

Answer 10

Excess of dichromate and heat under reflux

Question 11

Conditions of partial oxidation of 1o alcohol.

Answer 11

Limited amount of dichromate
Warm gently and distill as produced

Question 12

Describe reflux

Answer 12

• heating organic reactions mixtures over a long period of time.
• prevents the organic vapour from escaping, as it condenses them back to liquid

Question 13

Different features of reflux

Answer 13

1. Never seal top of condenser - build up of pressure - apparatus explode
2. Anti bumping granules - prevent vigorous, uneven boiling

Question 14

What does the oxidation of secondary alcohols produce

Answer 14

Ketone

Question 15

Reagent for oxidation of secondary alcohols

Answer 15

Potassium dichromate and dilute sulphuric acid

Question 16

Conditions for oxidation of secondary alcohol.

Answer 16

Heat under reflux

Question 17

What happens to 3o alcohol.

Answer 17

Can’t be oxidised because there is no hydrogen atoms bonding to the carbon w OH group

Question 18

Dehydration

Answer 18

The reaction of an alcohol into a Alkenes

Question 19

Reagent for dehydration

Answer 19

Concentrated sulfuric acid

Question 20

Conditions for dehydration

Answer 20

Warm under reflux

Question 21

Role of reagent dehydrate

Answer 21

Catalyst

Question 22

Type of react is dehydration

Answer 22

Eliminate forms a c=c bond

Question 23

Difference between the use of acidified potassium dichromate and tollens reagent / fehlings solution

Answer 23

• Potassium Dichromate is used for oxidation of alcohol to aldehydes and ketones
• Tollen’s Reagent or Fehling’s solution is used to distinguish between aldehydes and ketones
  Aldehydes will react by either producing a silver mirror w tollens or colour change from blue to a red precipitate formed with fehlings. Ketones will not react

Question 24

Give a reagent that can be used to distinguish between Butan-2-ol and 2-methylpropan-2-ol

Answer 24

Acidified potassium dichromate
Butan-2-ol - Colour change from orange to green
2-methylpropan-2-ol’

Question 25

Give the reagent that can be used to distinguish butanal from butanone

Answer 25

Reagent - fehlings solution Butanal - colour change from blue to a red precipitate formed Butanone - no colour change. Solution remains blue

Question 26

Test for Halogenoalkanes

Answer 26

- NaOH - Acidified AgNO3 Chloride - a white precipitate Bromide - cream coloured precipitate Iodide - Yellow precipitate

Question 27

Apparatus of reflux

Answer 27

Vertical condenser and pear shaped flask

Question 28

Conditions of oxidation for a high yield of carboxylic acid

Answer 28

1. Reflux 2. Excess potassium dichromate

Question 29

State one environmental problem that NO causes and what is used to remove it from exhaust gases formed in petrol fuelled cars.

Answer 29

It causes acid rain It is removed using a catalytic converter

Question 30

State what is meant by the term carbon neutral

Answer 30

No net emission of CO2 into the atmosphere

Question 31

In distillation, explain why the water should enter the condenser at the bottom and not the top.

Answer 31

To ensure that the condenser fills with water

Question 32

Describe how a student would use fractional distillation to collect a sample of ethanol

Answer 32

1. Turn on the water 2. Heat mixture using a Bunsen burner 3. Thugs causes the ethanol and water to evaporate and separate from other byproducts 4. Vapour passes up the fractionating column 5. Vapour and ethanol are separated in the column 6. Water condenses back into the flask 7. Observe thermometer to keep temperature at or below boiling point of ethanol 8. Only ethanol vapour with a little water passes into the condenser.