Alcohols

Question 1

Solubility of alcohols?

Answer 1

• alcohols dissolve in water bc H2 bonds with alcohol interact with H2 bonds within water
• solubility decreases as the chain length increases bc there are more hydrocarbons present in the system.

Question 2

Ethanol can be made by Steam Hydration and Fermentation?

Answer 2

Steam Hydration :
• ethanol is produced by steam hydration of ethene with a phosphoric acid catalyst
- ethene comes from cracking of heavier fractions
- reaction is reversible
- conditions : 300 degrees, 60atm
- process produces 100% ethanol, any unreacted ethene is recycled

Fermentation :
• exothermic process carried out by yeast in anaerobic conditions to prevent oxidation of ethanol to undesirable compounds e.g aldehyde which can affect flavour of product
• yeast produces enzyme zymase which converts sugars e.g glucose into ethanol and CO2
• enzyme works at optimum temp 30-40
• when solution reaches 15% ethanol, yeast does
• fractional distillation is used to increase conc. of ethanol
- ethanol used for alcoholic drinks and is safe as all other alcohols are toxic e.g methanol leading to blindness/death
- methylated spirits have a nasty rating substance so dye is added to stop people from drinking

Question 3

Advantages/Disadvantages of processes?

Answer 3

Advantage of Steam Hydration:
- faster reaction
- purer product
- continuous process
Disadvantage of Steam Hydration :
• ethene is non renewable resource, will become more expensive when raw materials run out
- expensive initial cost due to high technology equipment
- high energy costs for pumping to produce high pressures

Advantages of Fermentation:
• sugar is renewable
• production uses low level technology / cheap equipment

Disadvantages:
•ethanol made is not pure and needs purifying by fractional distillation
•Depletes land used for growing food crops

Question 4

Uses of methanol?

Answer 4

• unleaded petrol contains 5% of methanol to improve combustion
• important as a feedstock for manufacturing organic chemicals e.g plastics/dyes

Question 5

Classifying alcohols?

Answer 5

• Primary alcohol : the OH group is attatched to a C atom with at least 2 H atoms on it
• Secondary alcohol : the OH group is attatched to a C atom with at least 1 H atom on it
• Tertiary alcohol : OH group is attatched to a C atom with no H atoms on it

Question 6

Chemical reactions of alcohols?

Answer 6

1. Combustion
   - alcohols burn to produce CO2 + H2O
2. Reaction with sodium metal
   - alcohol reacts with Na to produce an alkoxide and hydrogen. The alcohol acts like an acid and gives an proton.
3. Dehydration of alcohol
   - term dehydration removes water from a molecule. A good dehydrating agent is H2SO4 @ 170 degrees. An alkene is made. A molecule of water is being taken from 2 adjacent C atoms.
   Steps:
   - draw out the molecule, remove water adjacent C atoms then write out structural formula and draw the different alkenes
4. Esterification
   - alcohols react with carboxylic acids to form esters + H20. CONCENTRATED H2SO4 = catalyst
   - esters are named backwards. You start with the alcohol who’s name become the prefix then add the acid-oate

Question 7

Oxidation of alcohols?

Answer 7

• Oxidation of Primary alcohols

• to an aldehyde + H2O ( loss of 2 H ) using potassium dichromate in dilute sulphuric acid. You would DISTIL the mixture so that lower BP aldehyde can over as soon as it’s made. If K2Cr2O7 was used as reagent there’s a colour change from Orange->green bc it’s being reduced to chromium (III)
• if oxidising agent used is in excess, further oxidation can occur to CARBOXYLIC ACID + H2O, 2 [O]. You would REFLUX this so that any aldehyde initially made goes back into flask to be further oxidised.

• Oxidation of Secondary alcohols:
- to a ketone using potassium dichromate and dilute sulphuric acid and heat under reflux.
Further oxidation does not occur as ketones can’t be oxidised. No H left on C

• Oxidation of Tertiary alcohols
- cannot be oxidised because there is no hydrogen atom bonded to the carbon with the OH group

Question 8

Boiling points/volatility?

Answer 8

• alcohols have low volatility due to their ability to form hydrogen bond between alcohol molcules.

• alcohols have higher boiling points than comparative alkanes as they have H2 bonds between molecules which are stronger than VDW forces on their own which alkanes have so more energy is needed to separate molecule
- as chain length increases, the surface contact increases, more stronger VDW between molecules so more energy is needed to separate them