Making Salts – GCSE Notes
Making Soluble Salts
To make a soluble salt, an acid is neutralised by adding a metal, a solid base, a solid metal carbonate, or a solution of an alkali. Soluble salts can be made by the process of:
- Titration
- Excess Reactant
Titration
Titration methods are carried out for a soluble base (an alkali) reacting with an acid to produce a soluble salt, e.g. reacting sodium hydroxide with hydrochloric acid to make sodium chloride. The problem with the reaction of a soluble base reaction with acid is that once all the acid has reacted, any excess base will not be visible; so there is no signal that all the acid has been neutralised. Therefore, the problem can be overcome by adding a third chemical into the reaction mixture called an indicator. Indicators are chemicals that change colour with a change in ph. The indicator is added to the acid and as the soluble base is added, the pH of the solution is raised until all the acid has reacted (been neutralized). The experiment can be run a number of times to gain a more accurate average value for the volume of base that needs to be added to neutralise the acid used. Once this accurate value has been determined, the experiment can be run one last time without any indicator. The volume of base that is required can be added carefully from the burette to produce a colourless solution, instead of the coloured solutions produced when indicator is added. This clear colourless solution can be heated to encourage crystals to form and then left to cool down slowly so that large crystals can form.