Topic 9d - Alcohols and Carboxylic Acids
Alcohols
A group of compounds that make up an homologus series
All contain the -OH functional group
General formula : CnH2n+1OH
Producing ethanol by fermentation
Process of using yeast to prduce alcohols from carbohydrates.
During fermentation, sugars like glucose are converted to ethanol and carbon dioxide.
The yeast contains the zymase enzyme.
Uses low temperatures, (25-40)
Batch process
Uses renewable resources
Process
1) Mix yeast and a glucose solution in a clean container and seal
2) Leave it in a warm place
3) Keep the temperature between 24-40 degrees so the ezymes can work at their optimum temperatures
4) Keep the mixture in anerobic conditions, to avoid the production of ethanoic acid, which is vinegar
5) When the concentration of alcohol reaches 10-20%, the reaction stops, as the yeast is killed by the alcohol
Fermentation produces a dilute concentration of ethanol
Fermented mixture can be distilled to produce a more concentrated alchol, like spirits
Carboxylic acids
Group of compounds that all contain the -COOH functional group.
Consits of a carbon atom that has formed a double bond with a lone oxygen and a single bond with an -OH group.
Names of carboxylic acids end in -anoic acid
Fractional distillation of ethanol
To make a concentration of ethanol above 20%, ethanol must be concentrated by fractional distillation of the fermentation mixture
Ethanol has a lower boiling point than water
When the mixture is heated, ethanol evapourates and the vapour rises up the fractionating column while the water stays liquid
A liebig condenser is used to condense the ethanol vapour by cooling it by passing cold water through it
The concentrated ethanol can then be collected in a seperate flask
Carboxylic acids are made by oxidising alcohols using an oxidising agent
Members of a homologus series often react in similar ways due to the presence of the same functional group
General formula is CnH 2n+1COOH, n is the number of carbon atoms in the molecule minus 1
Core practical - alcohols as fuels
Amount of energy given out when an alcohol combusts determines how good a fuel it is
More energy released, the better fuel it is
If you heat a known mass of water, you can measure the temperature rise and investigate the energy released
Method
1) Put some alcohol is a spirit burner and measure the mass of the burner and fuel using a mass balance
2) Measure 1000cm3 of distillsed water into a beaker on a tripod
3) Place the beaker in a draft excluder and place a lid after the thermometer to make sure that minmal energy is lost to the surroundings
4) Take the initial temperature of the water and then put the burner under the beaker, and light the wick
5) Continue heating the beaker, until the temperature of the water has risen by 20 degrees, then blow out the spirit burner
6) Immediately reweigh the spirit burner and subtract the initial mass to find the mass of the fuel that's been burned
7) Repeat the experiment using other spirit burners with other alcohols
Control variables
Mass/ volume of water
Height of beaker above wick
moles of alcohol
Results
The lower the mass of fuel needed increase the temperature, the better it is as a fuel
It's released more energy of fuel per gram
Hydration of ethene
Ethene reacts with water to produce ethanol
Conditions
Presence of phosphoric acid catalyst
Temperatures of 300-400 degrees
Pressuyre of 70 atm
Comparing fermentation and hydration
Fermentation
Uses renewable resources
Batch process
Slow rate
Porduces impure ethanol
Hydration
Uses finite resources
Continuous process
Fast rate
Produces much purer ethanol
Needs much higher temperatures
Needs lower temperatures
Biofuels
Pros
Renewable
Inexpensive, made through local materials
Carbon neutral carbon dioxide released equals the carbon dioxide abcorbed by plants
Cons
Reducded food for consumption
Loss of habitats due to land usage
Not widely available
A fuel produced from biological processes, not geological
Fossil fuels
Pros
Very efficient
Easily be transported
Generate large amounts of jobs
Cons
Released green house gases
Finite
Can cause illness