Module 3 - 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
CO32- (aq) + 2H+(aq) → H2O (aq) + CO2(g)
How can you test for sulfate
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 (Silver nitrate)
Why do you add HNO3
to test
for halide ions and why not
HCl?
To remove CO₃2-
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
