ch 14 alcohols

Question 1

what are the three ways to make alcohols

Answer 1

• hydration (electrophilic addition)
• fermentation
• hydrolysis (nucleophilic subsitution)

Question 2

alkene->alcohol

Answer 2

• hydration of alkene
• electrophilic addition
• H3PO4
• 300 degrees
• steam

Question 3

glucose->alcohol

Answer 3

• 37 degrees
• anerobic respiration
• yeast catalyst

Question 4

haloalkane->alcohol

Answer 4

• hydrolysis
• reflux
• nucleophilic subsitution
• NaOH aq

Question 5

evaluate hydration vs fermentation to produce alcohols

Answer 5

Hydration of ethene:
ADVANTAGES
100% atom economy
95% yield
Continuous operation
DISADVANTAGES
Ethene is obtained from crude oil which is a finite
energy resource

Fermentation:
ADVANTAGES
Glucose is a renewabl resource
DISADVANTAGES
The concentration of ethanol produced is about
15% ethanol. Distillation increases the
concentration of the alcohol
Food prices may increase with the new market
for glucose.

Question 6

Uses of methanol:

Answer 6

• clean burning fuel.
• feedstock for the chemical industry.

Question 7

Uses of ethanol:

Answer 7

• Ethanol in alcoholic drinks:
• perfumes.
• Ethanol as a fuel:

Question 8

The physical properties of alcohols are influenced by

Answer 8

their ability to form hydrogen bonds:

Question 9

Definition: Volatility

Answer 9

is the
ease that a liquid turns
into a gas. Volatility
increases as boiling point
decreases.

Question 10

Volatility and boiling points of alcohols

Answer 10

Alcohols have hydrogen bonds whereas their corresponding alkane (by Mr) has
London forces of attraction. As hydrogen bonds are stronger than London
forces they have higher boiling points. This means that their volatility is
much lower.

Question 11

The physical properties of alcohols are influenced by their ability to form
hydrogen bonds.

Answer 11

• Alcohols are soluble in water (or other polar solvents) as they will form hydrogen bonds with water (whereas alkanes will not).
• The solubility of alcohols decreases as the carbon chain increases.
• Only the first 3 alcohols are soluble in water.
• The hydrocarbon chain does not form
  hydrogen bonds and as it gets longer
  it interferes with the ability for the OH
  group to hydrogen bond with water.

Question 12

Polyols

Answer 12

Polyols are molecules that contain more than one –OH
group. When alcohols contain more than 1 hydroxyl group
they are known as diols (2), triols (3) etc.

Question 13

Classification of alcohols:

Answer 13

This is a Primary (1o) alcohol.
When the OH carbon (*) is
attached to only 1 other
carbon atom.

This is a Secondary (2o)
alcohol. When the OH
carbon (*) is attached to 2
other carbon atoms.

This is a Tertiary (3o) alcohol.
When the OH carbon (*) is
attached to 3 other carbon

Question 14

state the Reactions of Alcohols

Answer 14

• Combustion of alcohols
• Oxidation of alcohols:
• Esterification (condensation reaction.)
• Dehydration
• SUBSTITUTION

Question 15

Combustion of alcohols

Answer 15

• In a plentiful supply of oxygen, alcohols will burn to form carbon dioxide and water.

Question 16

Oxidation of alcohols:

Answer 16

To oxidise alcohols we use acidified potassium or sodium dichromate solution.
This is orange in colour and is a mixture of sulfuric acid, H2SO4/K2Cr2O7 or
H2SO4/Na2Cr2O7.

The orange colour is due to the Cr6+ ions in Cr2O72-
The potassium dichromate is an oxidising agent. This means that it can cause a
species to become oxidised which in turn means that the dichromate becomes
reduced. When this occurs the dichromate becomes green. The green solution
is due to Cr3+ ions.

Question 17

dichromate will remain
orange.

Answer 17

If the alcohol is resistant to oxidation

Question 18

If a large excess of dichromate is used
why might it be difficult to see if an
oxidation of the alcohol has occurred?

Answer 18

Excess of orange colour may mask the
formation of the green solution.

Question 19

Primary alcohol oxidise to form

Answer 19

Aldehyde or carboxylic acid

Question 20

Primary alcohol to an Aldehyde

Answer 20

Gentle heating of primary alcohols with acidified potassium dichromate make
an aldehyde. The aldehyde must be distilled immediately as it forms.

Question 21

Primary alcohol to a carboxylic acid

Answer 21

On stronger heating with excess acidified potassium dichromate the alcohol
will be completely oxidised passing through the aldehyde stage to form a
carboxylic acid.

Question 22

Secondary alcohol to a ketone

Answer 22

• Kr2Cr2O7 / h2so4
• heat
• reflux

Question 23

Tertiary alcohols oxidation?

Answer 23

Tertiary alcohols cannot be oxidised by acidified potassium dichromate. The
dichromate remains orange and no reaction occurs.

Question 24

drawing

Apparatus for the oxidation of primary alcohols:

Answer 24

Common errors include:
The water being connected the wrong way to the condenser.

A sealed system - never cut off the condensers as this makes a closed system (increases
the pressure - explosion).

The bulb of the thermometer at the incorrect height - should be parallel to condenser.

Question 25

Distinguishing between the products of oxidation:

Answer 25

Carboxylic acid:

If refluxed, a primary alcohol forms a carboxylic acid. The acid formed can be identified
by reaction with a base e.g. sodium carbonate. The reaction will produce bubbles as an
immediate observation.

Acid + metal carbonate → salt + water + carbon dioxide

Question 26

Preparation of esters

Answer 26

Warming a carboxylic acid and alcohol in a
boiling tube with a few drops of concentrated
sulphuric acid catalyst will produce an ester.

Question 27

Definition: Condensation is
the reaction

Answer 27

whereby two
molecules are joined with
the loss of a small molecule
e.g. water

Question 28

naming esters

Answer 28

alky alcaonate
alkyl alchohol
alcanote from carboxylic acid

Question 29

Esterification

Answer 29

An ester is formed when an alcohol is warmed with a
carboxylic acid in the presence of an acid catalyst.

Esterification is an example of a condensation reaction.

Question 30

Uses of esters

Answer 30

Are used as good solvents and in adhesives.

They have a sweet smell so are more known for their uses in perfumes and
food flavour additives:

Question 31

Definition: Dehydration

Answer 31

Definition: Dehydration is
an elimination reaction in
which water is removed
from a saturated molecule
to make an unsaturated
molecule.

Question 32

alcohol->alkene

Answer 32

• dehydration
• conc h2so4
• heat under reflux
• The H and OH
  atoms are lost from
  adjacent carbon
  atoms. The double
  bond then forms
  between these
  carbon atoms.