Alcohols
The An organic compound containing a hydroxyl group, -OH. The 'alcohol' in alcoholic drinks is ethanol, produced by the fermentation of sugars and found in wines, spirits and beers. form a A 'family' of organic compounds that have the same functional group and similar chemical properties. . Like all homologous series, the alcohols:
- have the same An algebraic formula that sets out a rule or trend which is followed by all members of a homologous series. For example, all non-cyclic alkanes have the general formula CnH2n+2.
- differ by CH2 in Chemical formula showing the actual number of atoms of each element in a molecule. from neighbouring A substance formed by the chemical union of two or more elements.
- show a gradual variation in physical The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point., such as their The temperature at which a substance rapidly changes from a liquid to a gas.
- have similar chemical properties
Functional group
The An atom, or group of atoms, that determines the main chemical properties of an organic compound. in the alcohols is the The functional group present in all alcohols, -OH. group, -OH. It is responsible for the typical reactions of alcohols. Take care not to confuse the -OH group with the hydroxide ion, OH-.
Structures
The table shows four alcohols, their molecular formulae and their structures.
Making ethanol by fermentation
Ethanol is the An organic compound containing a hydroxyl group, -OH. The 'alcohol' in alcoholic drinks is ethanol, produced by the fermentation of sugars and found in wines, spirits and beers. found in beer, wine and other alcoholic drinks. It is also used as a Material that is used to produce heat, like coal, oil or gas. for vehicles, either on its own or mixed with Fuels such as diesel and oil.. Ethanol can be produced by Type of anaerobic respiration carried out by yeast. and concentrated using In fractional distillation a mixture of several substances, such as crude oil, is distilled and the evaporated components are collected as they condense at different temperatures..
Fermentation
Fermentation is an Without oxygen. process:
glucose → ethanol + carbon dioxide
A unicellular fungus used in the brewing and baking industries., a type of single-celled A large group of eukaryotic organisms that contain single celled yeasts, moulds and mushrooms., provides the A protein which catalyses or speeds up a chemical reaction. needed for fermentation. If the yeast Basic unit of life. Unicellular organisms only have one cell. Multicellular organisms have many cells. become too cold, fermentation happens very slowly, or may not happen at all. If the yeast cells become too hot, their enzymes become To change the shape of an enzyme's active site, for example because of high temperatures or extremes of pH. Denatured enzymes no longer work. and fermentation stops.
The typical conditions needed for fermentation include:
- sugars A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution. in water, and mixed with yeast
- an air lock to allow carbon dioxide out, while stopping air getting in
- warm How warm or cold something is., 25-35°C
The yeast dies when the ethanol concentration reaches about 15%. Fermentation is a slow reaction and takes several days or weeks to finish. If air is present, the oxygen causes the ethanol to oxidise to ethanoic acid, so the drink tastes of vinegar.
Question
Describe and explain what happens to the limewater during the experiment shown above.
The limewater turns milky. This is because carbon dioxide is produced during fermentation, and passes through the limewater.