3.1.4 Qualitative Analysis Flashcards
1
Q
How do you test for carbonate ions?
A
- Reaction with H+ ions
- Add dilute acid (e.g. HCl, HNO3, H2SO4)
- There will be effervescence giving a colourless gas
- The gas will turn limewater cloudy as it is carbon dioxide
2
Q
What is the ionic equation for testing for carbonate ions?
A
CO32- (aq) + 2H+ (aq) -> CO2 (g) + H2O (l)
3
Q
How do you test for sulfate ions?
A
- Precipitation with Ba2+ (aq)
- Add dilute acid followed by barium chloride or barium nitrate
- HCl should be added with BaCl2 and HNO3 with Ba(NO3)2
- A white precipitate will form, which is barium sulfate
4
Q
What is the ionic equation for testing for sulfate ions?
A
Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)
5
Q
How do you test for halide ions?
A
- Precipitation with Ag+ (aq)
- Add dilute nitric acid followed by aqueous silver nitrate
- If chloride ions are present, a white precipitate will form
- If bromide ions are present, a cream precipitate will form
- If iodide ions are present, a yellow precipitate will form
- To test further, add ammonia solution (NH3)
- White precipitate will dissolve in dilute NH3
- Cream precipitate will dissolve in concentrated NH3
- Yellow precipitate is insoluble even in concentrated NH£
6
Q
What are the ionic equations for testing for halide ions?
A
Ag+ (aq) + Cl- (aq) -> AgCl (s)
Ag+ (aq) + Br- (aq) -> AgBr (s)
Ag+ (aq) + I- (aq) -> AgI (s)
7
Q
Why is acid added?
A
To prevent a false positive by removing any carbonate ions that would also react to form a white precipitate
8
Q
What order should these tests be done in?
A
- Carbonate
- Sulfate
- Halide
9
Q
How do you test for ammonium ions?
A
- Reaction with warm NaOH (aq) to form NH3
- Add aqueous sodium hydroxide and warm mixture
- A gas will form which turns damp red litmus paper blue
10
Q
What is the ionic equation for testing for ammonium ions?
A
NH4+ (aq) + OH- (aq) -> NH3 (g) + H2O (l)
