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 A description of the appearance of a substance or how it acts without involving chemical reactions. For example, state, melting point, conductivity, etc., such as their The temperature at which a substance rapidly changes from a liquid to a gas.
- have similar A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc.
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 solution of ethanoic acid.
General formula
The general formula for the carboxylic acids is CnH2n+1COOH (where n is the number of carbon atoms in the molecule, minus 1).
Remember that the O atoms are not joined to each other:
Worked example
Decanoic acid is a carboxylic acid. Its A collection of two or more atoms held together by chemical bonds. contain 10 carbon The smallest part of an element that can exist.. Predict the molecular formula of decanoic acid and explain your answer.
The formula will be C9H19COOH. This is because n = (10 – 1) = 9. So, 2n+ 1 = (2 × 9) = 18 + 1 = 19.
Question
Hexanoic acid is a carboxylic acid. Its molecules contain 6 carbon atoms. Predict the molecular formula of hexanoic acid.
The formula will be C5H11COOH.
Structures
The table shows four carboxylic acids, their molecular, displayed and structural formulae.
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 lower 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.