Alcohols UNIT 2 Flashcards
Products of incomplete combustion
Carbon dioxide
Water
Carbon
Carbon monoxide
When an alcohol undergoes complete combustion, what products are formed
Carbon dioxide and water
What are methylated spirits
Ethanol with a small percentage of poisonous methanol added to make it unfit to drink. Can be sold without the tax which is levied on alcoholic drinks. A purple dye is also added to show that it shouldn’t be drunk
Ways alcohols can be oxidised
Combustion or heating gently in stages
Primary alcohols are oxidised to….
Aldehydes, these can be further oxidised to carboxylic acids.
Secondary alcoholics are oxidised to…
Ketones (not oxidised any further)
Do aldehydes and ketones have pleasant or unpleasant smells
Pleasant
Process of oxidising ethanol to ethanal (an aldehyde)
Dilute acids and less potassium dichromate than is needed for complete oxidation to carboxylic acid. Mixture heated gently in reflux apparatus, receiver cooled in ice to reduce evaporation of product. Ethanal vaporises as soon as it’s produced and distils off. This stops it from being oxidised further to ethanoic acid. Unrea red ethanol remains in the flask
What does reflux mean
Vapour condenses and drips back into the reaction flask
Process of oxidising ethanol to ethanoic acid (carboxylic acid)
Conc. sulphuric acid and excess potassium dichromate. Mixture refluxed. Whilst this is happening, any ethanol or ethanal vapour condense and drip back into flask until all oxidised to acid. Distil of ethanoic acid
Process of oxidising a secondary alcohol to a ketone
Acidified dichromate added
3 types of alcohols
Primary
Secondary
Tertiary
Which one it is depends on which carbon atom the hydroxyl group is bonded to
What is the alcohols general formula
CnH2n+1OH
Ethanol can be produced industrially by…..
Fermentation
At the moment,most ethanol is being produced through what process? What is wrong with this method?
By steam hydration of ethene with phosphoric acid catalyst. The ethene comes from cracking heavy fractions of crude oil.
But in the future when crude oil supplies start running out, petrochemicals like ethene will be expensive
Explain the industrial production of ethanol by fermentation
Fermentation is an exothermic process, carried out by yeast in anaerobic conditions
Yeast produces an enzyme which converts sugars, such as glucose into ethanol and carbon dioxide
The enzyme works at an optimum temp of 30 to 40c, if too cold reaction is slow, if too warm the enzymes are denatured.
When the solution reaches about 15% ethanol, the yeast dies. Fractional distillation is used to increase the conc of ethanol
Fermentation is low tech, it uses cheap equipment and renewable resources. The ethanol produced by this method has to be purified though