3.1.4: 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 2- (aq) + 2H+ (aq) → H2O (aq) + CO2 (g)
How can you test for sulphate ions, SO4 2-?
● Add dilute hydrochloric acid and
barium chloride to the sample
What are the observations for a positive test of sulfate ions, SO4 2-?
White precipitate of barium sulfate is
produced
Write an equation for the sulfate ion test
Ba2+ (aq) + SO4 2- (aq) → BaSO4 (s)
What do you use to test for halide ions?
Acidified AgNO3
Why do you add HNO3 to test for halides and why not HCl?
To remove CO₃ 2-
Adding HCl would add Cl- ions, giving a false positive result
How can you test for a halide ion?
● Dissolve the 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 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 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 forms insoluble precipitate of BaCO3 and silver ions form insolube precipitate of Ag2SO4
What are cations also known as?
positive ions
