The alcohols and their reactions, making ethanol by fermentation, carboxylic acids as weak acids, and how an alcohol and an acid make an ester.
What you will learn
- Name alcohols and carboxylic acids and give their formulae
- Describe the reactions of alcohols and the conditions for fermentation
- Name the ester made from an alcohol and a carboxylic acid
Alcohols
Alcohols contain the OH functional group.
The name ends in -ol.
alcohols: CnH2n+1OH
Methanol CH3OH, ethanol C2H5OH, propanol C3H7OH, butanol C4H9OH.
- With sodium: fizzes, giving off hydrogen.
- Burn in air: carbon dioxide and water, so they are used as fuels.
- Small alcohols dissolve in water to give a neutral solution.
- Oxidised (for example by acidified potassium dichromate, or by microbes in air): carboxylic acid with the same number of carbons.
Ethanol is made by fermentation: sugar solution and yeast at about 30 °C, with air kept out so the yeast respires without oxygen and makes ethanol. Enzymes in the yeast are the catalyst; above about 40 °C they are denatured.
Comparing the two ways to make ethanol:
- Fermentation uses sugar from crops, a renewable resource, at a low temperature, but it is slow, is done in batches, and gives a dilute solution that has to be distilled.
- Hydration of ethene (ethene + steam, lesson 3) is fast, continuous and gives pure ethanol with a 100% atom economy, but it needs high temperature and pressure and its ethene comes from crude oil, a finite resource.
Balancing an alcohol's combustion, remember the oxygen atom already in the fuel: C2H5OH + 3 O2 → 2 CO2 + 3 H2O.
The rest of this lesson and its 13 practice questions are locked.
In this lesson
- Alcohols
- Try it: Check an Mr with the calculator
- Carboxylic acids
- Esters
13 practice questions, marked as you go; about 25 minutes in all.
Key terms
Burn, Dissolve in water, Fermentation, Hydration of ethene, COOH, Ethanoate, Ester, First
In this unit: Organic chemistry
Crude oil and the alkanes, combustion and cracking, then alkenes, alcohols, carboxylic acids, esters and polymers for separate Chemistry, with the formula and mass calculations that go with them.