Alcohols Flashcards
It is claimed that ethanol produced by fermentation is a carbon-neutral biofuel.
Write an equation for the photosynthesis of carbon dioxide and water into glucose.
Write an equation for the reaction of glucose into ethanol and name the process.
Write an equation for the complete combustion of ethanol.
Explain why the ethanol produced by this process may not actually be a carbon-neutral biofuel.
6CO2 + 6H2O -> C6H12O6 + 6O2 Photosynthesis
C6H12O6 -> 2C2H6O + 2CO2 Fermentation
2C2H6O + 6O2 -> 4CO2 + 6H2O Combustion
- fossil fuels burnt to transport ethanol and harvest crops
- heat energy required for fermentation
This statement appeared on a website: “The fact that bioethanol is a carbon-netural fuel outweighs the environmental disadvantages of producing it.”
Evaluate this statement.
Include in your answer:
-an outline of how bioethanol is produced
-relevant equations
-analysis of the environmental impacts.
Bioethanol is produced via fermentation of glucose using enzymes from yeast or zymase, at a temperature between 25 and 42 degrees celcius, and at a neutral pH.
Photosynthesis - 6CO2 + 6H2O -> C6H12O6 + 6O2
Fermentation - C6H12O6 -> 2C2H6O + 2CO2
Combustion - 2C2H6O + 6O2 -> 4CO2 + 6H2O
6CO2 taken in, 6 CO2 given out, so chemically carbon-neutral
HOWEVER:
- fossil fuels are burnt to harvest crops, heat reaction mixture for fermentation, and to transport bioethanol
- land is also used that could be used for food production.
In industry, fermentation is carried out at 35C rather than 25C.
Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature.
An advantage is a higher rate of reaction so more product can be made in a shorter amount of time
But a disadvantage is more heat energy is required to heat the mixture which costs more money
If fermentation is not carried out under anaerobic conditions, the ethanol will be contaminated by ethanoic acid.
How does this contamination occur? [1 mark]
- air will oxidise the ethanol into carboxylic acid
State the conditions for fermentation in industry.
- 25 - 42 degrees C
- neutral pH
- enzymes from yeast or zymase
- anaerobic conditions
What is the main advantage of using glucose from crops as the raw material for the production of ethanol, other than carbon-neutrality?
Crops are a sustainable source of fuel that can be grown at the same rate they are used
When an alcohol group is oxidised to a carboxylic acid, how many [O] are there and how many H2O are produced?
2 [O], 1 H2O
RH2(OH) + 2[O] -> ROOH + H2O
When an aldehyde is oxidised into a carboxylic acid, how many [O] are there and how many H2O are produced?
1[O], no H2Os.
RHO + [O] -> ROOH.
Draw the apparatus that you would use for a distillation of ethanol from an aqueous solution of ethanol.
Draw the apparatus that you would use for a reflux.
Explain why when using a Liebig condenser, water should go in at the bottom and come out from the top.
To ensure the entire condenser fills with water and so cooling is as effective as possible.
Ethanol can be oxidised by acidified potassium dichromate(VI) to ethanoic acid in a two-step process.
ethanol -> ethanal -> ethanoic acid.
In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried out under reflux.
Describe what happens when a reaction mixture is refluxed and why it is necessary, in this case, for complete oxidation to ethanoic acid. [3 marks]
- in a reflux, a mixture of liquids is heated to it’s boiling point for a prolonged period of time
- vapours which are produced are cooled and condensed and returned back to the reaction vessel
- which allows any ethanol and ethanal which vapourised to continue being oxidised to the acid.
