Alcohols

Question 1

Alcohol general formula

Answer 1

CnH2n+1OH

Question 2

Describe the shape of an alcohol

Answer 2

O 90° from C
H 104.5° from O

Question 3

Alcohol physical properties

Answer 3

OH leads to hydrogen bonding
Higher mp/bp than alkanes
Short chain alcohols, soluble in water (H bond between alcohol and water molecules)

Question 4

4 reasons alcohols are industrially important

Answer 4

Intermediates
Easily made
Easily converted to other compounds
Ethanol

Question 5

What 3 main compounds can alcohols be converted into

Answer 5

Aldehydes
Ketones
Carboxylic acids

Question 6

What is ethanol used for

Answer 6

Cosmetic solvent
Drug manufacture
Alcoholic drink manufacture

Question 7

Describe the hydration of alkenes

Answer 7

Steam added across double bond
Forms an alcohol

Question 8

Advantages and disadvantages of hydration of alkenes

Answer 8

A: fast, pure product, 95% yield, continuous
D: uses finite crude oil source, high energy cost (temp/pressure), high tech equipment

Question 9

Describe fermentation of glucose

Answer 9

Forms ethanol and carbon dioxide
Carbs —> sugar cane/beet
Yeast enzymes
Anaerobic respiration

Question 10

Advantages and disadvantages of fermentation of glucose

Answer 10

A: renewable source
D: carbon dioxide, greenhouse gas, global warming, slow, impure, fractional distillation needed, sugar cane takes up land for crops, high labour cost

Question 11

Halogenation

Answer 11

Addition of a halogen to an alcohol

Question 12

Conditions for hydration of alkenes (3)

Answer 12

300°C
60atm
solid phosphoric (V) acid catalyst

Question 13

Conditions for fermentation of glucose (4)

Answer 13

30-40°C
yeast
air kept out, prevent oxidation —> ethanoic acid
15% alcohol enzymes don’t function, fractional distillation, increase alcohol content

Question 14

Primary and secondary alcohol chlorination

Answer 14

Reactant: Anhydrous phosphorus (V) chloride, white solid
Conditions: Rigorous at rtp, no heating needed
Products: Makes choloralkane, phosphorus chloride, hydrogen chloride (white smoke)
Notes: Separate products via fractional distillation

Question 15

Tertiary chlorination

Answer 15

Reactant: HCl
Conditions: Concentrated HCl, shake, rtp
Products: tertiary chloroalkane, water
Notes: ?

Question 16

Bromination of alcohols

Answer 16

Reactant: KBr
Conditions: 50% concentrated H2SO4, warm
Products: Bromoalkane, water

Question 17

Iodination of alcohols

Answer 17

Reactants: Red phosphorus, iodine —> phosphorus triiodide
Conditions: heat under reflux
Products: iodoalkane, phosphoric acid (H3PO3)

Question 18

Dehydration of alcohols

Answer 18

Reactant: alcohol
Conditions: excess concentrated phosphoric acid, hot (170°C)
Products: alkene, water (removed from alcohol)
Notes: renewable alkene/polymer source, hydrogen that joins with OH to make water always taken from carbon adjacent to functional group

Question 19

Dehydration of alcohols mechanism description

Answer 19

O electron pair to lone H+
C-O to positive O
Adjacent H-C to C+
Double bond forms and H+

Question 20

3 types of oxidation

Answer 20

Complete
Incomplete
Sophisticated

Question 21

What do each characterisation of alcohols oxidise to form

Answer 21

Primary: aldehyde then carboxylic acid
Secondary: ketones
Tertiary: don’t oxidise

Question 22

Describe the oxidation of a primary alcohol

Answer 22

Reactant: alcohol
Conditions: potassium dichromate catalyst acidified with dilute H2SO4
Products: aldehyde (COH) then carboxylic acid (COOH)
Notes: dichromate ion reduced orange —> green, use H2SO4 not HCl otherwise acid is oxidised not alcohol

Question 23

Describe the oxidation of a secondary alcohol

Answer 23

Reactants: alcohol
Conditions: dilute H2SO4 acidified potassium dichromate
Products: ketone (CO)
Notes: orange potassium chromate ions —> green

Question 24

Describe the oxidation of a tertiary alcohol

Answer 24

Doesn’t occur
Would need to break a C-C not a C-H, stronger
Ketones/carboxylic acids don’t oxidise further
Can be oxidised via combustion

Question 25

What is the purpose of distillation

Answer 25

Separate substances with different boiling points
Purify a product (chlorination tertiary alcohol, collect at desired bp)
Stop a reaction at a certain point (aldehyde from oxidise primary alcohol)

Question 26

Distillation process (6)

Answer 26

Gently heat reaction mixture
Substances evaporate in ascending bp
Thermometer shows bp
Substances condense in condenser
Collect in conical flask
Anti bumping granules make boiling smoother

Question 27

Why use a reflux reaction

Answer 27

Stop flammable/volatile product loss
Time to react fully

Question 28

Reflux process (4)

Answer 28

Vertical Liebig condenser, everything evaporates
Drop back into reaction mixture/condense, keeps reacting
Heating usually electrical, water bath, hot plate (flammable product/reactants)
Anti bumping granules make boiling smoother

Question 29

Ways of removing impurities

Answer 29

Insoluble in water: separation to remove impurities that do dissolve
Use other solvents as long as desired product doesn’t dissolve in it
Or add solvent it does dissolve in then remove via distillation

Question 30

Removing impurities process (4)

Answer 30

Mixture in separating funnel, add solvent
Invert a few times, leave to settle, 2 layers form
Remove stopper, open tap, drain lower layer
Pour upper layer into separate flask

Question 31

Washing use, process and example

Answer 31

Remove left over reagents/unwanted side products
Add liquid and shake
Organic liquid + organic acid, add sodium hydrogen carbonate, reacts with acid to form salt, acid is catalyst, carbon dioxide made

Question 32

Drying process

Answer 32

Anhydrous salt
Bind to water, become hydrated
First go lumpy, add more till it looks like a snow globe
Drying agent removed via filtration

Question 33

2 anhydrous salts good for drying

Answer 33

Magnesium sulphate
Sodium sulphate
Calcium chloride