Tests For Ions Flashcards
Flame test : sodium
Yellow
Flame test : copper
Blue/green
Flame test : lithium
Red
Flame test : calcium
Red/orange
Flame test : potassium
Lilac
Sulphate ions test
Add hydrochloric acid to remove contaminants. Add barium chloride (soluble) to the solution. If sulphate ions are present, a white precipitate (barium sulphate) will form.
Precipitation reaction of aluminium cations
Forms white precipitate in a few drops of sodium hydroxide solution. This dissolves when more sodium hydroxide is added
Precipitation reaction of calcium cations
Forms a white precipitate when sodium hydroxide is added. No change happens when more is added
Precipitation reaction of copper cations (II)
Pale blue precipitate forms when sodium hydroxide solution is added
Precipitation reaction of iron cations (II)
Green precipitate is formed when sodium hydroxide solution is added
Precipitation reaction of iron (III)
Brown precipitate formed when sodium hydroxide solution is added
Test for carbonates
Add dilute hydrochloric acid to ionic substance so it can react. If it contains carbonate ions, it will give off carbon dioxide gas. Use a delivery tube to bubble this through limewater where it should turn from clear and colourless to cloudy
How to be more accurate in identifying flame colours
Use a spectroscope - detects different wavelengths to produce a line spectrum. They are fast, sensitive and accurate
How does flame emission spectroscopy work?
Electrons jump energy orbits as they gain energy from the heat of the flame but lose it by giving off visible light. The wavelength depends on the charge and electron arrangement which is specific to only one type of ion. The intensity indicates the concentration
Test for halides
Add silver nitrate (silver halides are insoluble). Add nitric acid first to remove contaminants. Chloride - white, bromide - cream, iodide - yellow
