Alcohols

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C14.4.1

Ethanol may be formed by a reaction between ethene and steam

14.4.2*

Ethanol is formed by the catalytic addition of steam to ethene

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14.4.3

Combustion of ethanol

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2C2H6 + 7O2 = 4CO2 + 6H2O

Complete Combustion of Ethane.

ethane+ oxygen carbon dioxide +water + energy2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(l)

The reaction is exothermic (it gives out heat)

The products are the same (carbon dioxide and water)

More oxygen is required for the complete combustionof ethane (compared to methane)giving four times the quantity of carbon dioxideand three times the quantity of water.

Trends The hydrocarbons become harder to ignite as the molecules

get bigger. This is because the bigger molecules don't vaporize so easily - the reaction is much better if the oxygen and the hydrocarbon are well mixed as gases. If the liquid isn't very volatile, only those molecules on the surface can react with the oxygen.

Bigger molecules have greater Van der Waals attractions which makes it more difficult for them to break away from their neighbours and turn to a gas.

Provided the combustion is complete, all the hydrocarbons will burn with a blue flame. However, combustion tends to be less complete as the number of carbon atoms in the molecules rises. That means that the bigger the hydrocarbon, the more likely you are to get a yellow, smoky flame.

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14.4.4

Ethanol can be used as a solvent and a fuel

Uses of ethanol

Drinks

The "alcohol" in alcoholic drinks is simply ethanol.

Industrial methylated spirits (meths)

Ethanol is usually sold as industrial methylated spirits which is ethanol with a small quantity of methanol added and possibly some colour. Methanol is poisonous, and so the industrial methylated spirits is unfit to drink. This avoids the high taxes which are levied on alcoholic drinks (certainly in the UK!).

As a fuel

Ethanol burns to give carbon dioxide and water and can be used as a fuel in its own right, or in mixtures with petrol (gasoline). "Gasohol" is a petrol / ethanol mixture containing about 10 - 20% ethanol.

Because ethanol can be produced by fermentation, this is a useful way for countries without an oil industry to reduce imports of petrol.

As a solvent

Ethanol is widely used as a solvent. It is relatively safe, and can be used to dissolve many organic compounds which are insoluble in water. It is used, for example, in many perfumes and cosmetics.

MAKING ALKENES IN THE LAB

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