What are alcohols?
A family of organic compounds (a homologous series) whose molecules contain a hydrocarbon chain and the -OH functional group, also known as ‘hydroxyl group’.
What is the general formula for alcohols?
CₙH₂ₙ₊₁OH
How can we use ethanol?
- In alcoholic drinks
- As a solvent
- As a fuel
- As a starting material to make chemicals in industry
How can ethanol be produced?
- Fermentation of sugars (such as glucose) by anaerobic respiration of yeast cells
- Reaction of ethene with steam (hydration).
What is ethanol made from?
Ethanol in alcoholic drinks is made from sugars/starch (from fruits e.g. grapes and barley/wheat seeds).
How is ethanol produced?
Plant material containing sugars is mixed with water and yeast. Enzymes in the yeast turn sugars into ethanol and carbon dioxide through fermentation.
What are the raw materials required for fermentation?
- Sugars
- Water
- Yeast
(Enzymes can be used as a catalyst)
What are the conditions required for fermentation?
- Optimum temperature of around 30°C
- Optimum pH of around 7
- Anaerobic conditions (absence of oxygen/air)
What process do we have to use to form more concentrated solutions of ethanol and why?
Fractional distillation - this is because the fermentation process only produces concentrations up to 15% as higher concentrations kill the yeast.
How does fractional distillation successfully produce ethanol?
Fractional distillation works because the boiling point of ethanol (78°C) is lower than the boiling point of water (100°C). The heated liquids evaporate and their vapours cool as they rise up the column. As ethanol has a lower boiling point, it remains a gas for longer and separates from water. As a result, the first fraction or distillate that is collected contains a higher percentage of ethanol.
Check teacher notes diagram SC23b slide 10.
What chemical properties do alcohols have?
- Produce carbon dioxide and water on complete combustion
- Can be oxidised to form compounds called carboxylic acids
- React with reactive metals (such as sodium), forming hydrogen gas as one of the products
- The larger the number of carbons, the less reactive the alcohol
What are carboxylic acids?
Organic acids, a homologous series with the carboxyl group (-COOH) functional group.
What is the general formula for carboxylic acids?
CₙH₂ₙ₊₁COOH
How is ethanoic acid produced?
By the oxidation of ethanol.
What are the physical properties of carboxylic acids?
- pH 3-4 (organic acids weaker than inorganic e.g. HCl)
- Very miscible (soluble) in water
What are the chemical properties of carboxylic acids?
- Neutralise alkalis/bases and react with carbonates to form CO₂ gas (as all acids)
- React with metals to form salt and H₂ (as all acids)
