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Flashcards in Quantitative Analysis Deck (10)
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Quantitative analysis

Relies on simple observations than measurements


Carbonate test

Add dilute nitric acid to sample
Collect gas released, bubble through lime water
+ve, cloudy


Sulphate test

Barium sulphate is very insoluble, used for sulphate test
Add barium ions to sample (Ba(NO3)2)(BaCl2)
+ve white precipitate

Do not use barium chloride if testing for halides afterwards, contaminate sample


Halide test

Silver halides, very insoluble
Add silver nitrate to sample
+ve, silver chloride, white precipitate, soluble in dilute
+ve, silver bromide, cream precipitate, soluble in conc
+ve, silver iodide, yellow precipitate, insoluble in con

Add aqueous ammonia to test solubility of precipitate as colours are hard to distinguish


Sequence of tests



Why test carbonates first

Only carbonates produce CO2
Can test without possibility of incorrect conclusion


Why test sulphates 2nd

A solution containing Ba2+(aq) ions are added
BaCO3 is white, insoluble in water
If sulphate test is carried out on carbonate, will get a white precipitate
Only test once no carbonates are present


Why test halides 3rd

A solution containing Ag+ ions are added
Ag2CO3, Ag2 SO4 are both insoluble, will form precipitates
Only test once no carbonates or sulphates are present


Mixture of ions

Carry out test in same sequence on same solution
Add nitric acid until no more CO2 released
Add excess of barium nitrate
Filter off precipitate
Add silver nitrate, other anions have been removed, precipitate must include halide ions
Add ammonia to confirm


Test for ammonium ions

Aqueous sodium hydroxide added to ammonium ions solution
Ammonia gas produced, v soluble in water
Heat solution to release gas
+ve, red damp litmus paper goes blue