chapter 15 - alcohols

Question 1

what’s a primary alcohol?

Answer 1

1 R group/ 2 hydrogen groups attached onto the carbon with the hydroxide group.

Question 2

what’s a secondary alcohol

Answer 2

2 R groups / 1 hydrogen group attached onto the carbon with an alcohol on.

Question 3

what’s a tertiary alcohol

Answer 3

where there are 3 R groups and no hydrogen groups attached to the carbon with the hydroxide group

Question 4

what’s an aldehyde

Answer 4

a C=O at the end of a carbon chain

name it by (al) eg methanal, pentanal

Question 5

what’s a ketone

Answer 5

C=O in the middle of a carbon chain

name it by stating where the C=O is. eg propanone, pentan-2-one

Question 6

what’s a carboxylic acid

Answer 6

a COOH group at the end of a carbon chain

eg, ethanoic acid, 2-methylpropanoic acid.

Question 7

what is hydration overall

Answer 7

a way ethanol is produced

hydration of ethene in the presence of an acid catalyst

Question 8

what is fermentation overall

Answer 8

a way of producing ethanol

fermentation of a wide variety of plant materials

Question 9

uses of ethanol

Answer 9

• as a solvent
• in cosmetics
• used in the manufacture of ethyl ethanoate and other esters
• in the production of ethoxyethane
• as a motor fuel blending agent

Question 10

what is hydration in producing ethanol. in detail

Answer 10

hydration of ethene
C2H4(g) + H2O(g) = C2H5OH(g)

fractional distillation is used

catalyst (concentrated H3PO4 or concentrated H2SO4)

temperature = 300 degrees celsius

pressure = 65 atm

fast process. takes seconds

continuous process

high equipment costs and energy costs. low labour costs

Question 11

fermentation to produce ethanol in detail

Answer 11

C6H12O6(aq) = 2CH3CH2OH(aq)+ 2CO2(aq)

catalysed by enzymes found in yeast, enzymes operate best around 37 degrees and normal atmospheric pressure.

oxygen free (anerobic process)

the maximum yield of ethanol that any one batch can achieve is around 15%. this is because at higher concs the enzymes are poisoned. to increase the concentration of ethanol solution obtained, it must be distilled.

the process is long. takes days

batch process

Question 12

What are the advantages of hydration

Answer 12

It is a continuous process

It’s produces a purer product which requires less refinement

Question 13

What are the disadvantages of hydration

Answer 13

ethene is non-renewable. It’s comes from crude oil

Question 14

What are the advantages of fermentation

Answer 14

Sugar is renewable. Uses renewable resources

The equipment is cheap. Lower equipment costs as there are low temperatures

Question 15

What are the disadvantages of fermentation

Answer 15

it is a batch process. Which is relatively slow

ethanol needs distilling As it is not pure. Costs more money to process it

Question 16

What is the difference between a continuous process and a batch process

Answer 16

A continuous process is a flow of product between every step of the process with no breaks.

A batch process involves a sequence of steps in a specific order which have to be repeated over and over

Question 17

Oxidation of alcohols overall

Answer 17

primary alcohols = aldehydes = carboxylic acids

secondary alcohols = ketones

tertiary alcohols cannot be oxidised

Question 18

is ethanol as a biofuel (produced by fermentation) carbon neutral?

Answer 18

During photosynthesis six carbon dioxide molecules are taken in
6CO2+6H2O=C6H12O6+6O2

During fermentation and combustion six molecules of carbon dioxide are released
C6H12O6=2C2H5OH+2CO2
2C2H5OH+6O2=4CO2+6H2O

Therefore there is no net release of carbon dioxide in theory

However this does not take into account transport, and machinery Which produces carbon dioxide blah blah blah blah blah and then

Question 19

Oxidation of primary alcohols into aldehydes

Answer 19

Example: ethanol
condensed equation:
CH3CH2OH+(O)= CH3CHO+H2O
Conditions: the alcohol is in excess. oxidising agent added in drops. Has to occur via distillation as this will prevent further oxidation
Oxidising agent: acidified potassium dichromate (K2Cr2O7)
Colour change: orange solution to green solution
product:ethanal.

Question 20

Oxidation of primary alcohols to carboxylic acids

Answer 20

eg:ethanol
Condensed equation:
CH3CH2OH+2(O)= CH3COOH+H2O
oxidising agent:(O) Acidified potassium dichromate (VI)
Conditions: heat on the reflux then distill the product.
Colour change: orange solution to green solution

Question 21

oxidation of secondary alcohols to ketones

Answer 21

Eg:propan-2-ol
Condensed equation:
CH3CH(OH)CH3+(O)=CH3C(O)CH3+H2O
Oxidising agent: acidified potassium dichromate
Conditions: heat on the reflux for completion
Colour change: Orange solution to green solution

Question 22

Oxidation of Tertiary alcohols

Answer 22

Tertiary alcohols cannot be oxidised at all, oxidation is not possible. This difference in chemical behaviour can be used to distinguish between tertiary alcohols and primary/secondary alcohols.

Question 23

What colour change would occur if a primary or secondary alcohol was heated with acidified potassium dichromate solution.

Answer 23

You would see a colour change from an orange solution to a green solution

Question 24

What colour change would occur if a tertiary alcohol was heated with acidified potassium dichromate solution

Answer 24

No reaction occurs, therefore the colour of the solution will remain orange and there will be no visible change.

Question 25

A test to distinguish between aldehydes and ketones is heating with fehlings solution. What would the observation with an aldehyde be versus a ketone.

Answer 25

Observation with an Aldehyde- from a blue solution to a brick red Precipitate

Observation with the Ketone-The solution will remain blue

Question 26

Another test to distinguish between aldehydes and ketones is to heat with Tollens reagent. What would the observations be with an aldehyde versus a ketone

Answer 26

Observation with an aldehyde-the solution will turn from a colourless solution to a silver mirror.

Observation with a ketone-The solution will remain colourless and there will be no visible change

Question 27

Describe in detail normal distillation (distillation)

Answer 27

This process is used to separate organic compounds and to prevent an organic reaction to going to completion.

For example to obtain a pure sample of a Ketone/oxidising a primary alcohol into an aldehyde.

The reactants are heated gently to the boiling point of the desired products. This desired product vaporises while the others remain in the pear-shaped flask.

• Anti-bumping granules (prevent rigourous bubbling/large bubbles forming)
• Water goes in at the bottom/lowest point
• One of the reactants or oxidising agent is added drop wise through the dropping funnel
• The thermometer measures the temperature of the vapours
• The distillate is collected in a conical flask that is sat in an ice bath to keep it as a liquid and stop the product from evaporating.

Question 28

Describe in detail fractional distillation

Answer 28

It allows substances to vaporise when heated, the fractionating column is not at the bottom and it is cooler further up.

• As the vapours rise up the fractionating column the different substances drop below their boiling point I’m temporarily collected at a particular level.
• The fraction with the lowest boiling point reaches the top, here it’s condensers, and runs down the condenser.
• The fraction is removed, and a separate flask/beaker is put at the end of the condenser. The temperature is then increased allowing collection of the next fraction to occur.
• This is repeated until all fractions are collected.