What is the carbonate test?
- Add dilute nitric acid
- If you see bubbles it could be carbonate
- Bubble it through limewater
- If it forms a white precipitate then CO2 is present
What is the equation for the carbonate test?
CO2 + Ca(OH)2 = CaCO3 + H2O
What is the sulfate test?
- Hydrochloric acid and barium chloride
- If a white precipitate forms then there are sulfate ions
What is the equation for the sulfate test?
Ba 2+ + SO4 2- = BaSO4
What is the halide test?
- Add aqueous silver nitrate to the solution
- Observe the colour of the precipitate
- Add aqueous ammonia to test the solubility
- As colours can be difficult to distinguish
How to determine chloride in the halide test?
- Forms a white precipitate
- Soluble in dilute NH3
How to determine bromide in a halide test?
- Forms a cream precipitate
- Soluble in conc. NH3
How to determine iodide ions in the halide test?
- Forms a yellow precipitate
- Insoluble in NH3
What is the correct order to do these tests and why?
1) Carbonate test - because this is the only one that forms bubbles so can be identified first.
2) Sulfate test - when barium ions are added a white precipitate is formed with the sulfate ions. However adding barium ion to a carbonate forms barium carbonate which is also a white precipitate.
3) Halide test - although the colours are distinctive if you add aqueous ammonia then other ions could dissolve in it.
What should you do if you have a mixture of ions?
- Add nitric acid in excess to remove all the carbonate
- After the sulfate test filter off the precipitate
What is the ammonium test?
- Aqueous sodium hydroxide is added to a solution of ammonium ion.
- Ammonia gas is produced but you are unlikely to see bubbles due to it being very soluble.
- Solution is warmed releasing the ammonia.
- Testing using indicator paper - which would turn blue.
