Carboxylic acids
The A homologous series of compounds that contain the carboxyl functional group, -COOH. form a A 'family' of organic compounds that have the same functional group and similar chemical properties. . Like all homologous series, the carboxylic acids:
- 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 carboxylic acids is the A functional group found in the carboxylic acids, -COOH. group, -COOH. It is responsible for the typical reactions of carboxylic acids, which are weak Substance producing more hydrogen ions than hydroxide ions when dissolved in water. . Vinegar is a dilute Mixture formed by a solute and a solvent. of ethanoic acid.
Structures
The table shows four carboxylic acids, their molecular formulae and their structures.
Acid properties
The carboxylic acids have the typical properties of acids. For example, they:
- When a substance breaks up and mixes completely with a solvent to produce a solution. in water to form Having a pH lower than 7.Mixture formed by a solute and a solvent. with Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. values less than 7
- react with Shiny element that is a good conductor of electricity and heat, and which forms basic oxides. to form a The substance formed when the hydrogen ion in an acid is replaced by a metal ion. and hydrogen
- react with A substance that reacts with an acid to neutralise it and produce a salt. to form a salt and water
- react with carbonates to form a salt, water and carbon dioxide
These properties are due to the –COOH functional group.
Making esters
Carboxylic acids can react with alcohols to make A type of organic compound formed in the reaction between an alcohol and a carboxylic acid.. Esters are Compounds that contain carbon atoms, joined by covalent bonds to other atoms (including other carbon atoms). which all contain the An atom, or group of atoms, that determines the main chemical properties of an organic compound. -COO-. Esters have fruity smells and can be used as The liquid in which the solute dissolves to form a solution..
The general equation for the formation of an ester is:
alcohol + carboxylic acid → ester + water
For example:
ethanol + ethanoic acid → ethyl ethanoate + water
Weak and strong acids - Higher
Carboxylic acids are weak acids. This means that their solutions do not contain many hydrogen ions compared with a solution of a strong acid with the same The concentration of a solution tells us how much of a solute has been dissolved in a solvent. Concentration is measured in moles per litre. The higher the concentration, the more particles of solute are present.. The pH of a weak acid will be higher than the pH of a strong acid, if their concentrations are the same.
In a solution of a strong acid, the molecules are fully ionised, but in a weak acid, very few of the molecules are To ionise is to convert an uncharged atom or molecule into a charged particle by adding or removing electrons..