(4.29C-4.33C) Alcohol + ethanol

What are alcohols?

Colourless liquids that dissolve in water to form neutral solutions

What is the functional group of alcohols?

-OH

What does, for example, propan-1-ol mean?

The -OH functional group is attached to the ‘first’ C, from R→L or L→R

What is the general formula for alcohols?

C_nH_2n+1OH

What are the three ways that ethanol can be oxidised?

Combustion

Aerobic oxidation

Oxidising agent

Describe the reactants, process and products of the combustion of ethanol.

ethanol + oxygen → water + carbon dioxide

ethanol burns with a blue flame

What happens to wine when it is left open outside?

Bacteria with use the oxygen from the air to oxidise the ethanol in the wine

producing a weak solution of ethanoic acid (which is used in vinegar)

Describe the reactants, process and products of the aerobic/microbial oxidation of ethanol.

ethanol + oxygen → ethanoic acid + water

Describe the reactants, process and products of the treatment of ethanol with an oxidising agent

Ethanol is heated with

potassium dichromate(VI) solution

in sulfuric acid

to form

ethanoic acid.

Slow process- heated for about an hour with a condenser above the flask to prevent escape

The potassium dichromate turns from orange to green

How is the oxidising agent written in equations?

[O]

What are the two ways that ethanol can be manufactured?

Hydration of ethene

Fermentation of glucose

Where do we get ethene from?

The cracking of hydrocarbons

Describe the process of the hydration of ethene.

Ethene + Water → Ethanol

Temp: 300 degrees C

Pressure: 60 - 70 atm

Catalyst: Phosphoric acid

After the reaction, the reaction chamber has ethene, ethanol and water.

Condenser used to extract the unreacted ethene.

Fractional distillation used to separate the ethanol and water.

What are the pros and cons of hydrating ethene to manufacture ethanol?

Pros:

• Pure ethanol is formed

• Fast process

• Continuous process- high yield

Cons:

• Ethene is from crude oil → non-renewable

• High temperatures and pressures → expensive

Describe the process of the fermentation of glucose to make ethanol.

glucose → carbon dioxide + ethanol

Sugar/starch is dissolved in water + yeast is added

The mixture is fermented between 25 - 35 degrees C, without oxygen.

Yeast has enzymes that break down sugar into ethanol via respiration.

Once the concentration of alcohol reaches 15%, the yeast is killed off.

Ethanol and water mixture separated by fractional distillation.

What are the pros and cons of fermenting glucose to manufacture ethanol?

Pros:

• sustainable

• lower temperatures and pressures

Cons:

• batch process as yeast is killed off

• impurity risk

• slower than hydration

Why does fermentation need to occur in the absence of air?

Yeast only breaks down glucose to respire anaerobically so there cannot be any oxygen available.

Why does fermentation need to occur at an optimum temperature?

The breaking down of glucose happens due to enzymes in the yeast

enzymes perform best at an optimum temperature:

• if temp. is too low, enzymes are slow

• if too high, enzymes denature, and stop catalysing reactions