1. Testing for ions and gases
Topic 8.4

2. What you need to know The following tests:
Cations - Iron(II), Iron(III), Copper(II), Aluminium, Zinc, Calcium and Ammonium
Anions – Nitrate, Chloride, Iodide, sulfate, carbonate
Gases- ammonia, carbon dioxide, chlorine, hydrogen, oxygen

3. Cations
Positive ions
Fe2+
Fe3+
Cu2+
Al3+
Zn2+
Ca2+
NH4+

4. Iron(II) - Fe2+ Dirty green precipitate Doesn’t dissolve in excess
In both sodium hydroxide and ammonia solution

5. Iron (III) - Fe3+ Red brown precipitate Doesn’t dissolve in excess
In both sodium hydroxide and ammonia solution

6. Copper(II)- Cu2+
Pale blue precipitate with sodium hydroxide doesn’t dissolve in excess
Pale blue precipitate with ammonia solution dissolves in excess to give a deep blue precipitate

7. Aluminium - Al3+
White precipitate doesn’t dissolve in excess sodium hydroxide
White precipitate does dissolve in excess ammonia solution

8. Zinc - Zn2+
White precipitate with sodium hydroxide and ammonia solution dissolves in excess of both

9. Calcium - Ca2+
White precipitate with sodium hydroxide and with ammonia solution
Doesn’t dissolve in excess of either!

10. Distinguishing Al3+, Zn2+ and Ca2+
With sodium hydroxide and ammonia
Dissolves in excess sodium hydroxide and ammonia
White precipitate
Doesn’t dissolve in excess of either sodium hydroxide or ammonia
Dissolves only in excess sodium hydroxide
Zn2+
Ca2+
Al3+

11. Ammonium ion - NH4+
Ammonias is displaced from its compounds when they heated with a strong base
Heat with sodium hydroxide- gas given off that turns damp red litmus blue

12. Anions
Negatively charged ions
NO3-
Cl- I-
SO42-
CO32-

13. Nitrate - NO3- Add sodium hydroxide and aluminium foil
Gas evolved that turns damp red litmus blue

14. Chloride - Cl- Add nitric acid and then silver nitrate solution
White precipitate

15. Iodide - I- Add nitric acid and then silver nitrate solution
Pale yellow precipitate

16. Sulfate - SO42-
Add a few drops of acid (not sulfuric) then barium nitrate or barium chloride solution
White precipitate

17. Carbonate - CO32-
Add acid
Bubbles of gas that turns limewater milky

18. Gases
NH3
CO2
Cl2 H2 O2

19. Damp red litmus paper turns blue
Ammonia NH3
Damp red litmus paper turns blue

20. Carbon dioxide CO2
Turns limewater milky

21. Bleaches damp litmus paper
Chlorine Cl2
Bleaches damp litmus paper

22. Hydrogen H2
Hold a lighted splint to the tube containing hydrogen, the gas burns with a squeaky pop
POP!

23. Relights a glowing splint
Oxygen O2
Relights a glowing splint

24. What you should know The tests for :
Cations - Iron(II), Iron(III), Copper(II), Aluminium, Zinc, Calcium and Ammonium
Anions – Nitrate, Chloride, Iodide, sulfate, carbonate
Gases- ammonia, carbon dioxide, chlorine, hydrogen, oxygen