E. alcohols

Question 1

Give the equation for the combustion of an alcohol

Answer 1

alcohol + O2 -> CO2 + H2O

Question 2

What is the reagent in chlorination

Answer 2

PCl5

Question 3

What are the conditions in chlorination

Answer 3

room temperature

Question 4

Give the reaction that takes place in chlorination

Answer 4

alcohol + PCl5 -> haloalkane (l) + POCl3 (l) + HCl (g)

Question 5

What observation can be used to identify a chlorination reaction

Answer 5

HCl gas is observed as ‘misty fumes’

HCl reacts with NH3 to form ammonium chloride, which is observed as ‘white smoke’

Question 6

Give two issues with the chlorination reaction

Answer 6

1) reaction produces HCl which is harmful
2) reaction has a low atom economy

Question 7

Give the reaction in which a chloroalkane is formed from a tertiary alcohol

Answer 7

alcohol + HCl -> chloroalkane + H2O

Question 8

What are the reagents in bromination

Answer 8

50% concentrated sulfuric acid and Na/KBr

Question 9

Give the two reactions that take place to form a bromoalkane

Answer 9

H2SO4 + 2NaBr -> 2HBr + Na2SO4
HBr + alcohol -> bromoalkane + H2O

Question 10

What are the reagents in iodination

Answer 10

red phosphorus (P) and I2

Question 11

What are the conditions for iodination

Answer 11

heat under reflux

Question 12

Give the two reactions that form an iodoalkane

Answer 12

2P + 3i2 -> 2PI3
PI3 + 3(alcohol) -> 3(iodoalkane) + H3PO3

Question 13

What is the reagent in a dehydration reaction of alcohols

Answer 13

concentrated phosphoric acid

Question 14

Give the reaction to form an alkene from an alcohol

Answer 14

alcohol -> alkene + H2O

Question 15

Why does is phosphoric acid not included in the elimination word equation

Answer 15

the water that is formed dilutes the concentrated phosphoric acid

Question 16

What are primary alcohols oxidised into

Answer 16

aldehydes
functional group:
O=C-H

Question 17

What are aldehydes oxidised into

Answer 17

carboxylic acids
functional group:
O=C-OH

Question 18

What are secondary alcohols oxidised into

Answer 18

ketones
functional group:
O=C-C

Question 19

What are tertiary alcohols oxidised into

Answer 19

tertiary alcohols do not undergo oxidisation

Question 20

What is the reagent in an oxidation reaction of alcohols

Answer 20

acidified potassium dichromate
K2Cr2O7

Question 21

Describe how to distinguish between tertiary, and primary and secondary alcohols

Answer 21

acidified potassium dichromate is an orange oxidising agent
when alcohols are oxidised, the orange dichromate ions are reduced to green chromium ions

Question 22

What solution is used to distinguish between primary and secondary alcohols

Answer 22

Fehling’s solution

Question 23

What observation is made if Fehling’s solution is added to an aldehyde

Answer 23

the aldehyde will be oxidised to a carboxylic acid
the Cu2+ ions will be reduced to Cu+ ion
this reaction results in the formation of a red precipitate
- copper (I) oxide (Cu2O)

Question 24

What observation will be made when Fehling’s solution is added to a ketone

Answer 24

ketones cannot be oxidised and so the mixture remains blue

Question 25

When should heating under reflux be used

Answer 25

when full oxidation is wanted - carboxylic acid - primary alcohol - ketone - secondary alcohol

Question 26

Why does heating under reflux ensure full oxidation

Answer 26

volatile reactants condense and fall back into the solution - this is important so reactants and products aren't lost and the reaction keeps occuring any products of oxidation remain in the reaction mixture

Question 27

Why is the end of the condenser not sealed in a reflux setup

Answer 27

to prevent a pressure build up

Question 28

What is the role of anti-bumping granules in reflux

Answer 28

to ensure the solution boils more evenly throughout - smoother boiling

Question 29

When should distillation be used

Answer 29

when we do not want complete oxidation e.g. to obtain an aldehyde rather than a carboxylic acid

Question 30

Why is distillation used to produce an aldehyde

Answer 30

when the aldehyde is formed, it is immediately distilled off as it has a much lower boiling point than the alcohol used to make it - the aldehyde is collected in the receiver