2.7 Alcohols and Carboxylic acids

Question 1

Two main methods of producing alcohols

Answer 1

Hydration and fermentation

Question 2

Hydration of alkenes

Answer 2

• produces alcohols from alkenes in the presence of an acid catalyst
• very high percentage yield - 1 product
• industrial process- high yield
• catalyst - phosphoric acid - increases rate without affecting yield
• 300 degrees celsius- compromise temperature as forward is exothermic so high yield would need a low temperature but would lead to a slow rate of reaction
• high pressure (60-70atm)- less moles of product so high yield favoured by high pressure, increases rate of reaction expensive when too high

Question 3

Fermentation - sugars are converted to alcohol

Answer 3

• catalysed by enzyme present in yeast
• sugar is dissolved in water
• yeast is added and mixture is left in a warm place
• production of alcoholic drinks
• cheaper than hydration - lower temperature needed
• lower percentage yield than hydration
Eg glucose –> ethanol and carbon dioxide

Question 4

After fermentation describe and explain how ethanol can be separated from the aqueous mixture left in the fermentation vessel

Answer 4

By fractional distillation as it has a boiling temperature of 80 degrees C

Question 5

What is a biofuel

Answer 5

Fuel that has been produced using a biological source

Question 6

Advantages of biofuels

Answer 6

• renewable - grow trees, animal waste material
• greenhouse gases - although they produce CO2 when burned they take some in during photosynthesis- carbon neutral overall
• economic and political security- countries without their own source of fossil fuels are affected bu changes in price + availability

Question 7

Disadvantages of biofuels

Answer 7

• land-use- deforestation to create land to grow plants for biofuels
• use of resources- need lots of water and fertiliser , short supply of water and water pollution
• carbon neutrailty?- building factories and transport raw material - CO2 production

Question 8

Alcohol dehydration to form alkenes

Answer 8

• water molecule is eliminated from the molecule and double bond is formed
• need a dehydrating agent/catalyst eg heated Al2O3 or concentrated H2SO4

Question 9

How can addition polymers be produced from fermentation without the need for crude oil?

Answer 9

Fermentation produces the primary alcohol which can be dehydrated to produce an alkene which is used in the production of addition polymers

Question 10

Primary alcohol

Answer 10

-OH joined to C that is not joined to more than 1 other C atom

Question 11

Secondary alcohol

Answer 11

-OH is joined to C that is joined to 2 other C atoms

Question 12

Tertiary alcohol

Answer 12

-OH joined to C that is joined to 3 other C atoms

Question 13

Answer 13

Primary

Question 14

Answer 14

Primary

Question 15

Answer 15

Secondary

Question 16

Answer 16

Tertiary

Question 17

Oxidation of primary alcohol

Answer 17

Primary alcohol –> aldehyde–> carboxylic acid

Question 18

Oxidation of secondary alcohol

Answer 18

Secondary alcohol–> ketones

Question 19

Oxidation of tertiary alcohol

Answer 19

No oxidation

Question 20

Use of acidified potassium dichromate (V)

Answer 20

Behaves as oxidising agent of alcohol
Orange to green
Primary + secondary- positive
Tertiary- negative

Question 21

Formation of carboxylic acid

Answer 21

Aldehyde produced from primary alcohol will undergo further oxidation to form a carboxylic acid
Secondary won’t

Question 22

Testing for carboxylic acids

Answer 22

React as acids with sodium hydrogencarbonate
Produce CO2
CO2 collected and tested using limewater- cloudy if it is CO2

Question 23

Description of carboxylic acids as acids

Answer 23

Weak- slightly dissociate in solution

Form H+ ion and carboxylate ion RCOO-

Question 24

Carboxylic acids and carbonates reaction

Answer 24

Carboxylate salt, water and carbon dioxide

Question 25

Carboxylic acids and hydrogen carbonates reaction

Answer 25

Carboxylate salt, water and carbon dioxide

Question 26

Carboxylic acid and base reaction

Answer 26

Carboxylate salt and water

Question 27

Carboxylate salt eg Na

Answer 27

CH3COO-Na+

Question 28

Propene can be formed by a dehydration reaction | Name a suitable reagent for this reaction

Answer 28

Concentrated sulphuric acid

Question 29

Give an oxidising agent that can be used, in acid solution, to oxidise primary alcohols to carboxylic acids and state what is seen as the reaction proceeds

Answer 29

``` Potassium dichromate (VI) Colour change from orange to green ```

Question 30

State the conditions of temperature and pressure used in the preparation of ethanol from ethene

Answer 30

300 degrees C | 60-70 atm

Question 31

Ethanol can be converted to ethanoic acid in an oxidation reaction. Give suitable reagents for this reaction

Answer 31

Acidified potassium dichromate (VI)

Question 32

Ethene can be used as the starting material in the industrial preparation of ethanol Name the catalyst used in this reaction

Answer 32

Phosphoric acid