3.5- Alcohols

Question 1

What is the bond angle for the H-C-H bonds and the C-O-H bonds

Answer 1

H-C-H bonds are 109.5 deg

C-O-H bonds are 104.5 deg

Question 2

What is the boiling point of alcohols

Answer 2

The alcohols have a relatively low volatility and high boiling points due to thier ability to form hydrogen bond between alcohol molecles

Question 3

What are the three different types of alcohols

Answer 3

Primary - 1 carbon attached to the one containing the OH
Secondary- 2 carbon attached to the one containing the OH
Tertiary - 3 carbon attached to the one containing the OH

Question 4

What are the reagents for the partial oxidation of a primary alcohol to aldehyde

Answer 4

Reagent- Potassium dichromate solution and dilute sulfuric acid
Conditions- Limited amount of dichromate, warm gently and distil out the aldhyde as it forms

Question 5

What is the observation from the oxidation of an alcohol

Answer 5

Orange to green

Question 6

What are the reagents/conditions for the full oxidation of primary alcohols

Answer 6

Reagents- Potassium dichromate solution and dilute sulfuric acid
Conditions- Use an excess of dichromate, and heat under reflux

Question 7

When do you carry out heat under reflux and what are the precautions

Answer 7

. Reflux is used when heating organic mixtures for long periods, the condenser prevebts organic vapours from escaping
. You should never seal the end of the condenser
. Anti bumping granules are added to the flask in both distillation and relux to prevens vigorous and uneven boiling by making small bubbles form instead of large bubbles
.When drawing do not drawlines between the flask and the condenser, condenser must have outer tube for water and the condenser must have 2 opening for water that are open

Question 8

What are the reagents/conditions for the full oxidation of a secondary alcohol to a ketone

Answer 8

Reagent- Potassium dichromate solution and dilute sulfuric acid
Conditions- Heat under reflux

Question 9

Why can’t tertiary alcohols be oxidised

Answer 9

Tertiary alcohols cannot be oxidised at all by potassium dichromate, this is becuase there is no hydrogen atom bonded to the carbon with OH

Question 10

What are the 2 different ways to distinguish between aldehydes and ketones

Answer 10

Tollens reagent-

. Aldehydes are oxidised into carboxylic acid, silver mirror forms with ketones there is no visible change

Fehlings solution-

. Aldehydes are oxidised into the carboxylic acids, blue copper ions change to a red precipitate and ketones do not react

Question 11

How can you test for the prescence of carboxylic acid

Answer 11

Addition of sodium carbonate, it will fizz and produce carbon dioxide

Question 12

What are the reagents/conditions for the reaction of Alcohol > Alkene

Answer 12

Reagents- Conc sulufirc or phosphoric acid
Conditions- Warm under reflux
Type of reaction- Acid catalysed elimination

Question 13

How do you form ethanol via fermentation

Answer 13

. glucose > ethanol + carbon dioxide
C6H12O6 > 2 CH3CH2OH + 2 CO2
The conditions needed are: •Yeast •No air •temperatures 30 –40oC

The optimum temperature for fermentation is around
38oC
At lower temperatures the reaction is too slow.
At higher temperatures the yeast dies and the enzymes
denature.
Fermentation is done in an absence of air because the
presence of air can cause extra reactions to occur.
It oxidises the ethanol produced to ethanoic acid
(vinegar).

Advantages
•sugar is a renewable resource
•production uses low level technology / cheap
equipment

Disadvantages
•batch process which is slow and gives high production
costs
•ethanol made is not pure and needs purifying by
fractional distillation
•depletes land used for growing food crops

Question 14

How do you form ehtanol from ethene

Answer 14

CH2=CH2 (g) + H2O (g) > CH3CH2OH (l)
Type of reaction- Hydration/addition
Definition - Hydration is the addition of water to a molecule

Essential Conditions
high temperature 300 °C
high pressure 70 atm
strong acidic catalyst of conc H3PO4

advantages: •faster reaction
•purer product
•continuous process (which means cheaper manpower)

Disadvantages:
•high technology equipment needed (expensive initial costs)
•ethene is non-renewable resource (will become more expensive when raw materials run out)
•high energy costs for pumping to produce high pressures

Question 15

Describe ethanol production from fermentation and whether it is a biofuel

Answer 15

Can be argued that it is carbon neutral, carbon dioxide is give off when the biofuel is burnt would have already been extracted from the air by photosynthesis when the plan grew, there would be no net CO emission to atmosphere

Question 16

What are the different equations to show no net contribution to CO2

Answer 16

6 CO2 + 6 H2O > C6H12O6 + 6 O2

This is the removal of CO2 via photosynthesis

C6H12O6 > 2 CH3CH2OH + 2 CO2
2 CH3CH2OH + 6O2 > 4 CO2 + 6 H2O

This is the production of CO2 by fermentation and combustion, when 1 mole of glucose is fermented 2 moles of CO2 are emitted, the two ethanol molecules will then also form 4 molecules of CO2

Overall for every 6 molecules of CO2 absorbed 6 moles of CO2 are emitted

However this does not take into accoun the energy that is needed to irrigate plants, fractionally distillate the ethanol, and travel which all use fossil fuels