2. This is ethane, an alkane. Many carboxylic acids are based on alkanes but with one of the methyl groups replaced by a carboxyl group.

3. This is ethane, an alkane. Many carboxylic acids are based on alkanes but with one of the methyl groups replaced by a carboxyl group.

4. This part of the carboxyl group is a carbonyl group, C=O.

5. This part of the carboxyl group is a hydroxyl group, –OH.

6. The carboxyl group is often shown as -COOH, but you can see that the two oxygen atoms are not joined together.

7. To name a carboxylic acid you need to know the number of carbon atoms it contains.

8. To name a carboxylic acid you need to know the number of carbon atoms it contains.

9. This gives the first part of the carboxylic acid’s name.

10. A carboxylic acid is named by adding oic acid to the prefix given by its number of carbon atoms.

11. The number of carbon atoms in the carboxylic acid is used for naming purposes.

12. The number of carbon atoms in the carboxylic acid is used for naming purposes.

13. But the carboxylic acid group is usually treated separately in the formula.

14. More than one carboxylic acid group can be present in a compound.

15. If there are two carboxylic acid groups the name ends in dioic acid.

16. This compound has two carbon atoms and two carboxylic acid groups, so it is ethanedioic acid.

17. Ethanedioic acid is a toxic acid also called oxalic acid. It is found in rhubarb leaves.

18. Ethanedioic acid is often shown like this.

19. This is benzene.

20. Carboxylic acid groups can be attached to benzene ring.

21. This is benzenecarboxylic acid.

22. However, it is usually just called benzoic acid.

23. It is usual to use the skeletal formula of benzoic acid to keep things simple.