Testing for ions and gases (T2) Flashcards
In a “flame test” what colour does sodium burn?
Sodium burns bright yellow orange
In a “flame test” what colour does lithium burn?
Lithium burns red with pink tones
In a “flame test” what colour does potassium burn?
Potassium burns lilac / lavender
In a “flame test” what colour does calcium burn?
Calcium burns bright red orange
In a “flame test” what colour does strontium burn?
Strontium burns red orange (similar to calcium)
In a “flame test” what colour does barium burn?
Barium burns yellow green
In a “flame test” what colour does copper burn?
Copper burns bright blue green
If we wanted to detect ammonium ions (NH4+) in a substance, what do we do?
We add sodium hydroxide (NaOH) and warm gently.
If there is ammonia present, a pungent gas is produced, which is NH3.
NH4 + OH -> NH3 + H2O
Ammonium ions + hydroxide ions -> ammonia + water.
Ammonia has a characteristic sharp, choking smell. It makes damp red litmus paper turn blue. It forms a white smoke of ammonium chloride when it comes into contact with hydrogen chloride gas, from concentrated hydrochloric acid.
Sodium hydroxide is useful for detecting certain cations - name three of these ions and explain what happens…
Copper II
CU2
- when mixed with sodium hydroxide this will form a blue precipitate
Iron II
Fe2+
- when mixed with sodium hydroxide this will form a green precipitate
Iron III
Fe3+
- when mixed with sodium hydroxide this will form a brown precipitate
If testing for anions, what do we do? Given examples using chloride ions, bromide ions and iodide ions…
If testing for anions, we group the substances together and judge them by the precipitate formed…
Chloride ions + nitric acid + silver nitrate -> white precipitate which is formed from silver chloride
Cl- + HNO3(aq) + AgNO3 -> AgCl
(^^ other substances are produced from this reaction but the AgCl is insoluble so will form as a powder)
Bromide ions + nitric acid + silver nitrate -> cream precipitate which is formed from silver bromide
Iodide ions + nitric acid + silver nitrate -> yellow precipitate which is formed from silver iodide
If testing for SO4 2- what reactants would we use?
We would use barium chloride and hydrochloric acid which would form a white precipitate
If testing for CO3 2- what reactants would we use?
We would use HCl and the result would be a production of CO2
How do we test for halide ions?
To test for halide ions (ions of the group 7 halogen elements), dilute nitric acid and sliver nitrate solution are added to the test solution. Different coloured precipitates (insoluble products) will be formed to show the presence of different halide ions.
How do you see if a solution contains sulphate ions?
You can test to see if a solution contains sulfate ions by using barium chloride. If barium chloride solution is added to a sample of water containing sulfate ions, barium sulfate is formed. Barium sulfate is insoluble in water, and will be seen as a white precipitate.
How would we test for chloride ions?
You can test to see if a solution contains chloride, bromide or iodide ions by using silver nitrate. If silver nitrate solution is added to a sample of water containing halide ions the silver halide is precipitated. This is because the silver halides are all insoluble in water.
