chapter 14: alcohols

Question 1

what is the functional group of the alcohols?

Answer 1

-OH
hydroxyl

Question 2

how do you name alcohols?

Answer 2

add the suffix -ol

Question 3

what is the simplest alcohol?

Answer 3

methanol
CH3OH

Question 4

what are the properties of alcohols compared to alkanes with the same number of C atoms?

Answer 4

less volatile
higher melting points
greater water solubility

Question 5

how can you explain the polarity in alcohols?

Answer 5

they have a polar O-H bond due to the difference in electronegativity.
they have weak London forces.
strong hydrogen bonds between polar O-H groups.

Question 6

how can you explain the low volatility and boiling points in alcohols compared to alkanes with the same number of C atoms?

Answer 6

in the liquid state, hydrogen bonds hold the alcohol together, they must be broken to turn it into a gas.
this requires more energy than overcoming the weak London forces in alkanes.

Question 7

how can you explain the solubility of alcohols?

Answer 7

a compound that can form H bonds is more water-soluble.
alcohols are soluble in water because H bonds can form between the polar O-H group and the water molecules.

Question 8

what happens to solubility as the chain length increases in alcohols?

Answer 8

decreases.
influence of the OH group decreases.

Question 9

how do you classify alcohols?

Answer 9

primary, secondary or tertiary.

Question 10

what are primary alcohols?

Answer 10

-OH group is attached to a carbon atom which is attached to 2 H atoms and one alkyl group (CH3).

Question 11

what is a secondary alcohol?

Answer 11

-OH group is attached to a carbon atom which is attached to one H atom and 2 alkyl groups.

Question 12

what is a tertiary alcohol?

Answer 12

-OH group is attached to a carbon atom which is attached to 3 alkyl groups and no H atoms.

Question 13

what do alcohols produce in combustion?

Answer 13

carbon dioxide and water.

Question 14

what type of reaction is the combustion of alcohols?

Answer 14

exothermic.
as the number of C atoms in the chain increases, the quantity of heat released per mole increases.

Question 15

how can primary and secondary alcohols be oxidised?

Answer 15

with an oxidising agent:
potassium dichromate acidified with dilute sulfuric acid.

Question 16

what is the colour change if the alcohol is oxidised?

Answer 16

orange to green

Question 17

what can primary alcohols be oxidised to?

Answer 17

aldehydes or carboxylic acids.

Question 18

how can primary alcohols produce aldehydes?

Answer 18

gently heated with acidified potassium dichromate.
aldehyde is distilled out as it forms, which prevents further reactions or formation of a carboxylic acid.

Question 19

how can primary alcohols produce carboxylic acids?

Answer 19

heated strongly under reflux with an excess of acidified potassium dichromate.
reflux ensures the aldehyde oxidises to a carboxylic acid.

Question 20

what are secondary alcohols oxidised to form?

Answer 20

ketones.

Question 21

how do secondary alcohols produce ketones?

Answer 21

heated under reflux with oxidising mixture (K2Cr2O7).

Question 22

what is a dehydration reaction?

Answer 22

water molecule removed from the starting material.

Question 23

what does dehydration of an alcohol produce?

Answer 23

alkene

Question 24

how do alcohols produce alkenes?

Answer 24

dehydration.
heated under reflux in the presence of an acid catalyst
(H3PO4 or (H2SO4).

Question 25

what type of reaction is dehydration?

Answer 25

elimination

Question 26

what do alcohols produce when they react with hydrogen halides?

Answer 26

haloalkanes

Question 27

what type of reaction forms haloalkanes from alcohols?

Answer 27

substitution

Question 28

how are haloalkanes produced from alcohols?

Answer 28

substitution reactions.
heated under reflux with sulfuric acid and a sodium halide to form HBr.
HBr reacts with the alcohol to form the haloalkane and a water molecule.