Alcohols

Question 1

What is the functional group of alcohols?

What is the suffix and prefix for naming alcohols?

Answer 1

-OH functional group (hydroxyl group) which is bonded to a carbon chain

-ol suffix and hydroxy- prefix

Question 2

What can alcohols be classified as and what does that depend on?

Answer 2

They can be classified as primary, secondary or tertiary alcohols

This depends on the number of carbon atoms directly attached to the carbon atom attached to the OH group

Question 3

How do you identify which is a primary, secondary or tertiary alcohol?

Answer 3

Primary - bonded to one other carbon

Secondary - bonded to 2 other carbons

Tertiary - bonded to 3 other carbons

Question 4

When do alcohols undergo elimination reactions?

What is another name for the reaction and why?

Answer 4

When heated with concentrated sulfuric acid at 450K

Dehydration reaction because water is eliminated

Question 5

Define dehydration

Answer 5

Dehydration is when water is lost from a compound

Question 6

What is the difference between a dehydration reaction and a condensation reaction?

Answer 6

In both reactions water is formed however in dehydration the water comes from one molecule whereas in condensation the water comes from 2 molecules

Question 7

What are 2 ways alcohol can be made in industry?

Answer 7

Direct hydration of Ethene with steam
Industrial Fermentation

Question 8

What are 3 products that can be used for industrial fermentation?

Answer 8

Sugar cane
Molasses ( a product of refining sugar cane)
Starch (from potatoes or corn)

Question 9

What is the product of industrial fermentation?

Answer 9

A mixture of water and about 15% ethanol by volume

Question 10

Why is there a limited amount of alcohol produced with fermentation?

Answer 10

No more alcohol is produced because the yeast is denatured by the alcohol

Question 11

What is the equation for the fermentation of glucose to form ethanol?

Include the 4 conditions

Answer 11

Glucose (aq) —> 2(ethanol) (aq) + 2(carbon dioxide) (g)

Aqueous solution of glucose
Yeast catalyst at 310K temp
1 atm pressure
Anaerobic conditions

Question 12

How would you separate the mixture of water and ethanol formed during fermentation?

Answer 12

Fractional distillation

Question 13

Explain why those conditions are used in fermentation? (3)

Answer 13

High temperatures would denature the enzymes in the yeast

Normal pressure are used as no gases involved in the reaction

If oxygen present this may oxidise the ethanol to ethanoic acid

Question 14

What can ethanol be used as?

Answer 14

Fuel for cars (Brazil)

Question 15

What 3 renewable sources can ethanol be made from?

Answer 15

Sugar cane
Corn
Maize

Question 16

What is ethanol made from renewable sources called

Answer 16

Bio ethanol

Question 17

What are biofuels

Answer 17

They are fuels made from living (raw materials)

Question 18

Write a series of equations to support the statement that ethanol produces by fermentation is carbon neutral

Answer 18

Learn the 3 equations !!!!!!!
Slide 29

Question 19

Why is the ethanol produced by fermentation carbon neutral

Answer 19

The amount of carbon dioxide released is equal to the amount of carbon dioxide absorbed when forming the glucose - this makes it carbon neutral

Question 20

Define carbon neutral

Answer 20

A process in which net carbon dioxide emission is zero

Question 21

Why are biofuels not carbon neutral
Give an example

Answer 21

They produce less carbon dioxide overall

Because fossil fuels are used in the production of biofuels

For example in making fertilisers for the growing plants and machinery used to harvest the crops

Question 22

What is an ethical issue linked to making biofuels

Answer 22

Crops that could be used to feed people are used to provide raw materials for biofuels instead

This could cause food shortages or increases in the price of food

Question 23

What are 3 economic factors related to the formation of ethanol

Answer 23

Human Resources - more people needed to produce biofuels than are needed to produce petrol and diesel

Increased income - for farmers

Lower fuel prices - biofuels limit the demand for fossil fuels, helping to reduce increases in fuel prices

Question 24

What are primary alcohols oxidised to and how

Answer 24

Aldehydes by an oxidising agent
For example an aqueous solution of acidified potassium dichromate

Question 25

What is the symbol for an oxidising agent called

Answer 25

An O in square brackets

Question 26

What are the 3 definitions for oxidation

Answer 26

Gain of oxygen
Loss of hydrogen
Loss of electrons

Question 27

How is further oxidation prevented when aldehydes are prepared by the reaction of a primary alcohol with an oxidising agent

Answer 27

The aldehyde is distilled off as soon as it is formed and collected

Question 28

How can aldehydes be further oxidised to carboxylic acids? (Primary alcohols)

Answer 28

If excess oxidising agent is used and the reaction is done under reflux

Question 29

How does reflux for carboxylic acids work

Answer 29

Once the aldehyde is formed it is condensed back into the reaction mixture and forced to react further

Question 30

What are the 2 products of oxidation of primary alcohols

Answer 30

Aldehydes then carboxylic acids

Question 31

What can secondary alcohols be oxidised to and how

Answer 31

They can oxidised to ketones by using an oxidising agent

(Acidified potassium dichromate)

Question 32

Why can’t tertiary alcohols be oxidised
What is an exception

Answer 32

There are no hydrogen atoms attached to the carbon bonded to the OH group so no hydrogen can be removed

Under extreme conditions when carbon - carbon bonds are broken

Question 33

Describe the reaction that gives the basis for testing for primary and secondary alcohols

Answer 33

The reaction of acidified potassium dichromate with alcohols

It is orange but when it reacts with a secondary and primary alcohol it is reduced to chromium (111) ions which are green

However since tertiary alcohols can’t be oxidised by potassium dichromate, it has no effect and does not change colour

Question 34

What functional group do aldehydes, ketones and carboxylic acids all contain

Answer 34

The carbonyl functional group C = O

Question 35

What is the suffix for aldehydes, ketones and carboxylic acids

Answer 35

Aldehydes -al

Ketones -one

Carboxylic acids -oic acid

Question 36

How can aldehydes and ketones be distinguished and why

Answer 36

They can be distinguished using a
mild oxidising agent

The presence of the C-H bond in aldehydes allows aldehydes to be oxidised to carboxylic acids so aldehydes are mild reducing agents

Question 37

What is Tollen’s Reagent?

Answer 37

It is ammonical silver nitrate

[Ag(NH3)2]NO3
Simplified to [Ag(NH3)2]+

Question 38

How can Tollen’s Reagent be used to test for aldehydes / ketones?

Answer 38

A reaction is shown by a silver mirror (a silver metal) forming which only occurs when an aldehyde is present

There is no reaction with a ketone therefore no visible change

Question 39

What is Fehling’s Solution

Answer 39

It is a blue solution containing copper 2+ ions in an alkaline solution (NaOH)

Question 40

How can Fehling’s solution be used to test for aldehydes / ketones

Answer 40

A reaction is shown by the blue solution forming a brick red precipitate if an aldehyde is present

There is no reaction with ketones therefore no visible changes