1. Sunday, April 23, 2017
Alcohols
L.O: To understand the structure of alcohols and describe some reactions involving alcohols

2. Do you remember making wine in year 8?
Alcoholic drinks contain the alcohol ethanol. The drink is produced by fermenting plant sugars
What is the combustion equation for ethanol?

3. Why does beer / wine smell and taste of vinegar when it is left out?
Ethanol is oxidised into ethanoic acid by microbes which live in the air
Ethanol can also be oxidised by some oxidising agents like potassium dichromate

4. Alcohols
Alcohols (which are organic compounds as they contain carbon) have an –OH functional group, with the general formula
CnH2n+1OH
Methanol – CH3OH
Ethanol – C2H5OH
Propanol – C3H7OH
Different alcohols are part of the same homologous series as they have the same general formula

5. What do you observe when sodium is reacted with water
KVE

6. Alcohol As Solvents
Alcohols such as methanol and ethanol can dissolve most compounds that water dissolves but they can also dissolve substances that water cannot, such as oils, fats and hydrocarbons
Ethanol is the solvent for perfumes and aftershaves (it can mix with the oils (giving the smell) and the water)
Methylated spirits (meths) is ethanol with other chemicals added to it – meths are used as paint cleaners and fuels (though they are poisonous to drink so are dyed)

7. Ethanol
Ethanol is also useful as a fuel – for use in cars and other vehicles, it is usually mixed with petrol

8. Producing Ethanol – Hydration of Ethene
Ethanol can be produced in 3 major ways. You need to know the advantages and disadvantages of each method
Ethene, which is obtained from crude oil, can be reacted with steam under high temperature and pressure to form pure ethanol.
Ethene + Steam  Ethanol
C2H H2O  C2H5OH
Conditions = 300oc, 60-70atmospheres
Advantages
100% atom economy (See 7.1)
95% yield
Produces 96% pure ethanol
Disadvantages
Feedstock is non-renewable.
Ethene must be produced by cracking which requires energy.
Process requires a lot of energy.

9. Producing Ethanol – Fermentation of Sugar
For thousands of years humans have been producing ethanol by fermentation of sugar. Common feed stocks are maize, corn and sugar cane.
Glucose  Ethanol + Carbon Dioxide
C6H12O6  2C2H5OH + 2CO2
Conditions = 25-37oc, 1atmosphere
However the product is impure as concentrations higher than 15% denature the enzymes killing the yeast. To purify it distillation is used, which uses energy.
Advantages
Uses renewable feedstock
Operates at low temperatures and pressures
Carbon neutral fuel source
Disadvantages
Produces impure ethanol
Atom economy is 51%
Still requires fossil fuels for purification
Feed stock needs to be grown which takes land which could be used to grow food instead.

10. Exam Questions
Method 1 is the least sustainable as it uses ethene which comes from crude oil and is not renewable. Methods 2 and 3 use renewable resources which can be regrown.
Atom economy. A process which produces less waste is more sustainable. If waste products can be used elsewhere the process is more sustainable.

11. Exam Questions Sodium fizzes slowly
Sodium fizzes violently on surface of water
No reaction
Ethanol and water both contain O-H groups so react similarly. However hexane only contains C-H and C-C bonds so is unreactive.

12. Exam Questions
High concentrations of ethanol denature the enzymes in yeast killing it.
Fractional Distillation
The mixture of ethanol and water is heated. Ethanol has a lower boiling point than water so evaporates and is collected first.

13. Exam Questions
High concentrations of ethanol denature the enzymes in yeast killing it and the reaction does not complete. Also other reactions take place using the glucose.

14. Exam Questions
At high temperatures the enzymes in the yeast denature killing it. However at low temperatures there is little energy for the reaction to take place and the reaction is too slow.

15. Exam Questions

16. Kerboodle alcohol ‘on your marks’

17. Ethene + Steam  Ethanol
Ethanol can be manufactured by reacting ethene (from cracking crude oil) with steam –phosphoric acid is used as a catalyst: -
Ethene + Steam  Ethanol
C2H4+ H2O C2H5OH
In the reaction ethanol is the only product – the process is continuous as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced
These features make it an efficient process, but as ethene is made from crude oil, which is a non-renewable resource, it cannot be replaced once it is used up and it will run out one day

18. Ethanol & Fermentation
Ethanol can also be made via fermentation – sugar from plant material is converted into ethanol and carbon dioxide…
Enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen (this is a renewable resource): -
C6H12O6  2C2H5OH + 2CO2
More than 90% of the world’s ethanol is made by fermentation