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 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 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
Ba^2+ (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 halide ions and not HCl?
To remove CO3^2-
Adding HCl would introduce 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 precipitate
Soluble in concentrated aqueous ammonia only
Ag+ (aq) + Br- (aq) ———> AgBr (s)
Write the result and equation for I- test
Yellow precipitate
Insoluble in dilute and concentrated 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
