Topic 3.5 - Alcohols

What is the functional group

of an alcohol?

Hydroxyl group -OH

What is the general formula

of an alcohol?

C n H 2n+1 OH

How do you name alcohols

(one prefix, one suffix)?

Hydroxyl- or -OH

What kind of intermolecular

forces do alcohols have?

Why?

Hydrogen bonding, due to the electronegativity

difference in the OH bond

How do alcohols’ m.p. And

b.p. Compare to other

hydrocarbons’ of similar C

chain lengths? Why?

Higher, because they have hydrogen bonding →

stronger than Van der Waals forces

Are alcohols soluble in

water? Why does solubility

depend on chain length?

Soluble when short chain - OH hydrogen bonds

to hydrogen bond in water

Insoluble when long chain - non-polarity of C-H

bond takes precedence

What makes an alcohol

primary?

C bonded to OH is only bonded to one other C

atom

What makes an alcohol

secondary?

C bonded to OH is bonded to two other C atoms

What makes an alcohol

tertiary?

C bonded to OH is bonded to three other C

atoms

How can ethanol be made

from crude oil?

Hydration of ethene via electrophilic addition

(phosphoric acid catalyst H₃PO₄)

What are the advantages

and disadvantages of this

method?

Advantages - fast, continuous process, ethanol

has a high purity

Disadvantages - not renewable as from crude oil

How can ethanol be made

by fermentation?

Plant carbohydrates broken down and

fermented by enzymes in yeast →

ethanol

What conditions are needed

for this reaction to take

place?

Enzymes in yeast as catalyst, 35°C, anaerobic

conditions

Write an equation for the

reaction which takes place.

C 6 H 12 O 6 (aq) → 2C 2 H 5 OH + 2CO 2

What are the advantages

and disadvantages of this

method?

Advantages - renewable as from plants

Disadvantages - slow, batch process, enzymes

stop working at 15% alcohol so solution is not

pure, needed to be fractionally distilled

In the future, how might

most ethene be made? Why

is it not made like this at the

moment?

Dehydrate ethanol made by fermentation →

ethene

Not economical at the moment

Define carbon neutral

No net addition of CO 2 to the atmosphere -

carbon dioxide released when combusted =

carbon dioxide absorbed as a plant

Explain how using ethanol

in petrol engines could be

considered to be carbon

neutral.

Carbon dioxide released in fermentation and

combustion = carbon dioxide absorbed when

growing

Why would it probably not

be entirely carbon neutral to

use ethanol?

Other “carbon costs” associated with it e.g.

Transport

What is a commercial fuel

that uses ethanol? What

else does it contain and

why?

Methylated spirits - methanol (toxic, so it can't be

drunk)

Write an equation for the

combustion of ethanol.

C 2

H 5

OH (l) + 3O 2 (g) → 2CO 2 (g) + 3H 2

O (l

What is an elimination

reaction?

The removal of a smaller molecule from

a larger one

Which group leaves the

parent molecule in the case

of alcohols?

OH and a H (to form water)

What physical conditions

are needed for the

elimination reaction from

alcohols to alkenes? (2

alternatives)

Excess hot concentrated sulphuric acid or pass

vapour over hot aluminium oxide

Draw a mechanism for the

dehydration of ethanol.

Draw a method for

dehydration of ethanol in the

lab.

What forms if you partially

oxidise a primary alcohol?

An aldehyde

What conditions are needed

to partially oxidise a primary

alcohol?

Dilute sulphuric acid, potassium

dichromate (VI), distill product as it’s

produced, gentle heating

Write an equation for the

partial oxidation of ethanol

CH 3

CH 2

OH (l) + [O] → CH 3

CHO (g) + H 2

O (l)

What forms if you fully

oxidise a primary alcohol?

A carboxylic acid

What conditions are needed

for this reaction?

Concentrated sulphuric acid, potassium

dichromate (VI), reflux for about 20 mins, strong

heating

Write an equation for the full

oxidation of ethanol

CH 3

CH 2

OH (l) + 2[O] → CH 3

COOH (g) + H 2

O (l)

What forms if you oxidise a

secondary alcohol?

A ketone

Why can it not be oxidised

further and why can’t a

tertiary alcohol be oxidised?

A carbon-carbon bond would have to break

What conditions are needed

for the oxidation of a

secondary alcohol?

Concentrated sulphuric acid, potassium

dichromate (VI), reflux for about 20 mins, strong

heating

Write an equation for the

oxidation of propan-2-ol.

CH 3 CH(OH)CH 3 (l) + [O] → CH 3 COCH 3 (g) + H 2 O (l)

What is an aldehyde? What

is its functional group?

Molecule with C=O group at the end of a carbon

chain, carbonyl functional group (C=O)

How do you name

aldehydes? Give an

example.

Suffix -al

e.g. ethanal

What is a ketone? What is

its functional group?

Molecule with C=O group in the middle of a carbon chain,

carbonyl functional group (C=O)

How do you name ketones?

Give an example?

Suffix -one

e.g. propanone

What is a carboxylic acid?

What is its functional group?

Molecule with a COOH group, which has to be at

the end of a carbon chain.

Carboxyl functional group (made up of carbonyl

C=O and hydroxyl -OH group)

How do you name

carboxylic acids? Give an

example

Suffix -oic acid

e.g. propanoic acid

What does the Tollens’ test

give a positive result for?

aldehydes

What is in Tollens’ reagent?

How does this react with the

substance to be tested?

Silver nitrate in NH 3 (aq) - oxidises aldehydes but

not ketones

Complex silver (I) ions reduced to Ag(s)

How do you carry out the

Tollens’ test?

Add equal volumes of substance being tested

and tollen’s reagent to a test tube, leave in water

bath for 10mins and observe any changes

What is the result of the

Tollen’s test for aldehydes

and ketones?

Aldehydes - silver mirror forms (solid Ag)

Ketones - no visible change

What does Fehling’s

solution give a positive test

result for?

aldehydes

What is in Fehling’s? How

does this react with the

substance to be tested?

Blue copper (II) complex ions - gentle oxidising

agent

Reduced to Cu + ions (brick red)

What conditions do you

need to use the Fehling’s

solution?

Heat

What result do aldehydes

and ketones give in the

fehlings test?

Aldehydes- brick red ppt

Ketones- no visible change