Qualitative Analysis Flashcards
What are anions also known as?
Negative ions
How can you test for carbonate ions, CO3 (2-)?
Add strong acid to the sample
Collect the gas produced
Pass through lime water
What are the observations for a positive test of carbonate ions, CO3 (2-)?
Fizzing
Limewater turns cloudy
Write an equation for the carbonate ion test
CO3 (aq) + 2H+ (aq) —> H2O (aq) + CO2 (g)
How can you test for sulfate ions?
Add dilute hydrochloric acid and barium chloride to the sample
What are the observations for a positive test of sulfate ions?
White precipitate of barium sulfate is produced.
Write an equation for the sulfate ion test.
Ba2+ (aq) + SO4 (aq) —> BaSO4 (s)
What do you use to test for halide ions?
Acidified AgNO3
Why do you add HNO3 to test for halide ions and why not HCl?
To remove CO3
Adding HCl would add Cl- ions, giving a false positive result
How can you test for a halide ion?
- Dissolve sample in water
- Add aqueous silver nitrate
- Record the colour change
- If difficult to distinguish the colour add aqueous ammonia, first dilute ammonia then concentrated ammonia
- Note the solubility of the precipitate
Write the result and equation for Cl- test
White precipitate, soluble in dilute aqueous ammonia
Ag+ (aq) + Cl- (aq) —> AgCl (s)
Write the result and equation for Br- test.
Cream ppt, soluble in only concentrated aqueous ammonia only
Ag+ (aq) + Br- (aq) —> AgBr (s)
Write the result and equation for I- test
Yellow precipitate, insoluble in concentrated and dilute aqueous ammonia
Ag+ (aq) + I- (aq) —> AgI (s)
When testing for carbonate, sulfate and halide ions, in which order should the tests be carried out and why?
- Carbonate test
- Sulfate test
- Halide test
Because barium ions form insoluble precipitate of BaCO3 and silver ions form insoluble precipitate of Ag2SO4
What are cations also known as?
Positive ions
