Topic 6 - Alcohols

Question 1

What is the general formula for an alcohol?

Answer 1

C_n H_2n+1OH

Question 2

Describe the boiling points of alcohols.

Answer 2

They have much higher boiling points compared to their respective alkanes, due to the present of hydrogen bonding between their hydroxyl groups.

Their boiling points also increase as number of carbon atoms increase, due to a higher number of London forces present.

Question 3

Describe the solubility of alcohols.

Answer 3

Smaller alcohols are soluble in water, because there are enough hydrogen bonds being made and broken to dissolve.

However , larger alcohols cannot dissolve in water, because the hydrocarbon tail does not form hydrogen and not enough energy is being released to compensate.

Question 4

What is a primary alcohol?

Answer 4

One alkyl group is attached to the carbon of the hydroxy group

Question 5

What is a secondary alcohol?

Answer 5

Two alkyl groups attached to the carbon of the hydroxy group

Question 6

What is a tertiary alcohol?

Answer 6

Three alkyl groups are attached to the carbon of the hydroxy group

Question 7

How can alcohols be produced on an industrial scale?

Answer 7

The fermentation of sugars

The hydration of ethene

Question 8

How can alcohols be prepared in a laboratory?

Answer 8

1. hydration of alkenes
2. reduction of ketones, aldehydes and carboxylic acids
3. hydrolysis of halogenoalkanes
   
   1. hydrolysis of esters

Question 9

What are the conditions of producing ethanol from ethene?

Answer 9

• phosphoric acid catalyst
• 300ºC
• 70 atm

Question 10

Is the reaction of producing ethanol from ethene endo or exothermic?

Answer 10

Exothermic

Question 11

What are the three types of reactions alcohols can undergo?

Answer 11

Substitution, elimination and oxidation

Question 12

alkali metal + alcohol → ?

Answer 12

alkoxide and hydrogen

Question 13

alcohol + carboxylic acid → ?

Answer 13

ester and water

Question 14

What are the conditions required for carboxylic acid + alcohol?

Answer 14

Reflux and acid catalyst

Question 15

alcohol + halogen halide → ?

Answer 15

nucleophilic substitution to produce halogenoalkane and water

Question 16

Why can iodoalkanes not be made by substitution of an alcohol?

Answer 16

The sulfuric acid catalyst oxidises hydrogen iodide

Question 17

What are the conditions required for alcohol + hydrogen halides?

Answer 17

reflux and H2SO4

Question 18

alcohol + phosphorus pentachloride → ?

Answer 18

hydrogen chloride gas

chloroalkane

phosphorus trichloride oxide

Question 19

What is the test for hydrogen chloride gas?

Answer 19

The misty fumes form dense white smoke of ammonium chloride when conc. ammonia solution is held near

Question 20

What is the method of oxidation of an alcohol?

Answer 20

1. heating the alcohol with aqeuous potassium dichromate acidified with dilute sulfuric acid
2. it will turn from orange to green

Question 21

What are the stages of oxidation in a primary alcohol?

Answer 21

First stage = aldehyde

Second stage = carboxylic acid

Question 22

What conditions are required for an aldehyde to be oxidised to a carboxylic acid?

Answer 22

Reflux

Excess oxidising agent

Question 23

What is a secondary alcohol oxidised into?

Answer 23

A ketone

Question 24

What are the tests to differentiate between a primary and secondary alcohol?

Answer 24

1. Oxidise both substances
2. Fehling’s solution or Tollen’s reagent

Question 25

How is Fehling’s Solution used to test for alcohols?

Answer 25

Contains blue Cu²⁺ ions

Only aldehydes will react as they are oxidised into a carboxylic acid

The solution will turn from blue to red as the Cu²⁺ ions are oxidised into CuO

Question 26

How is Tollen’s Reagent used to test for alcohols?

Answer 26

silver and ammonia is produced, showing as a silver mirror on the surface

Question 27

How is an alkene obtained from an alcohol?

Answer 27

Heating the alcohol using a sulfuric acid catalyst at 180C