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Unit 2 Module 2 Notes

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CHEMISTRY

2.2.1 ALCOHOLS HIGH MELTING AND BOILING POINTS OF ALCOHOLS

Because of the presence of hydrogen bonds between alcohol molecules

LOW VOLATILITY OF ALCOHOLS

Because of high boiling points Harder to turn from a liquid into a gas

SOLUBILITY


Alcohols dissolve in water Hydrogen bonds form between alcohol and water molecules Solubility decreases as the chain length increases
 A larger non-polar hydrocarbon chain doesn't form hydrogen bonds with water molecules

INDUSTRIAL PRODUCTION OF ETHANOL

Hydration of ethene Fermentation

HYDRATION OF ETHENE

Reaction of ethene with steam H2C=CH2 (g) + H2O (g)  CH3CH2OH (l)

CONDITIONS FOR HYDRATION OF ETHENE

Carried out at high temperature and moderate pressure (300⁰C 60 atm) In the presence of an acid catalyst (H3PO4)

PROCESS OF HYDRATION OF ETHENE




Reversible reaction Only 5% of ethene is converted each time the reagents pass through the reactor Unreacted gases pass through the reactor again 95% conversion, overall 100% atom economy

FERMANTATION FROM SUGARS

Carbohydrates (sugar or starch) are converted into ethanol and CO2 (g) C6H12O6 (aq)  2CH3CH2OH (aq) + 2CO2 (g)

CONDITIONS FOR FERMENTATION


Low temperatures (below 37⁰C so enzyme doesn't denature) Catalysed by yeast (enzyme in yeast) Absence of air - anaerobic (prevent oxidation of ethanol)

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PROCESS OF FERMENTATION

14% alcohol by volume of ethanol

ETHANOL IN ALCOHOLIC DRINKS

Made via the fermentation process

ETHANOL IN METHYLATED SPIRITS


Consists of ethanol, methanol and dye Toxic and undrinkable Used as solvent for removing paint or ink stains

USES OF METHANOL


Used as a petrol additive to improve combustion Used as a feedstock Can be converted into ethanol and ethanoic acid

PRIMARY ALCOHOLS

The -OH group is attached to a carbon atom with no alkyl groups

SECONDARY ALCOHOLS

The -OH group is attached to a carbon atom bonded to two alkyl groups

TERTIARY ALCOHOLS

The -OH group is attached to a carbon atom bonded to three alkyl groups

COMBUSTION OF ALCOHOLS


In plentiful supply of oxygen Forms carbon dioxide and water E.g. C2H5OH (l) + 3O2 (g)  2CO2 (g) + 3H2O (l)

OXIDISING AGENTS FOR OXIDATION OF ALCOHOLS



Uses an oxidising agent Represented by [O]
Oxidising agents are H+/ Cr2O72Oxidising mixtures are potassium dichromate (K2Cr2O7) and sulfuric acid (H2SO4)

ACIDIFIED POTASSIUM DICHROMATE

Changes colour from orange to green during the oxidation

OXIDATION OF PRIMARY ALCOHOLS


Alcohol  aldehyde using distillation (-OH to -CHO) Alcohol  carboxylic acid using reflux (-OH to -COOH) Aldehyde  carboxylic acid using reflux (-CHO to -COOH)

OXIDATION OF SECONDARY ALCOHOLS

Alcohol  Ketone using reflux (-OH to C-CO-C)
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