96577
Testing for metal ions
- flame tests (3 common ways)
- different metal ions give off different
coloured flames when solutions of those
ions are heated in a bunsen burner flame
- spray metal compound solution into a bunsen burner flame
- use wooden splints soaked overnight in the metal compound solution
- use a loop of nichrome wire to hold a small volume of solution in the flame
- if nichrome wire used - must be cleaned between each flame test.... dip
loop into concentrated hydrochloric acid and hold in flame.....process
repeated until wire no longer affects the flame colour...... traces of sodium
ions are particuarly difficult to remove
- if nichrome wire used - must be cleaned between each flame test.... dip
loop into concentrated hydrochloric acid and hold in flame.....process
repeated until wire no longer affects the flame colour...... traces of sodium
ions are particuarly difficult to remove
- different metal ions give off different
coloured flames when solutions of those
ions are heated in a bunsen burner flame
- lithium ( crimson)
- sodium (yellow)
- potassium (lilac)
- calcium (red)
- barium (green)
- hydroxide precipitates
- copper and iron form coloured compounds
- coloured hydroxide precipitate is
formed when a few drops of sodium
hydroxide solution are added to
solutions of metal ions
- eg Cu+2 + OH = Cu(OH)2
- eg Cu+2 + OH = Cu(OH)2
- copper(ii) ( blue )
- iron(ii) ( green )
- iron(iii) (brown)
- aluminium , calcium and magnesium
ions form hydroxide precipitate with
sodium hydroxide solution.
- difficult to tell apart as they are all white
- though..... aluminium hydroxide
precipitate dissolves to form a
colourless solution when excess
sodium hydroxide solution is added
- though..... aluminium hydroxide
precipitate dissolves to form a
colourless solution when excess
sodium hydroxide solution is added
- difficult to tell apart as they are all white
- copper and iron form coloured compounds
- Testing for negative ions
- Carbonate ions
- compounds containg carbonate ions react with dilute acids to form carbon dioxide
- eg.....drops of hydrochloric acid added to calcium
carbonate causes bubbling on the surface of the
solid
- eg.....drops of hydrochloric acid added to calcium
carbonate causes bubbling on the surface of the
solid
- most carbonates are insoluble in water
........HOWEVER sodium carbonate is soluble
- sodium carbonate
solution addded to dilute
acid causes brief
bubbling
- sodium carbonate
solution addded to dilute
acid causes brief
bubbling
- limewater, calcium hydroxide solution is used
as a comfirmatory test for production of
CO2...........white precipitate of calcium
carbonate formed when CO2 is bubbled
through limewater
- Ca(OH)2 (aq) + CO2 (g) = CaCO3 (s) + H2O (l)
- Ca(OH)2 (aq) + CO2 (g) = CaCO3 (s) + H2O (l)
- compounds containg carbonate ions react with dilute acids to form carbon dioxide
- Sulfate ions
- barium sulfate insoluble in water BUT not barium chloride
- white precipitate of barium sulfate forms when barium chloride solution is added to solutions containing sulfate ions
- eg........... Na2SO4 (aq) +BaCl2 (aq) = 2NaCl (aq) + BaSO4 (s)
- eg........... Na2SO4 (aq) +BaCl2 (aq) = 2NaCl (aq) + BaSO4 (s)
- white precipitate of barium sulfate forms when barium chloride solution is added to solutions containing sulfate ions
- barium sulfate insoluble in water BUT not barium chloride
- Halide ions
- formed by halogens
- silver fluoride is soluble in
water but other silver halides
are insoluble
- their insolubility is basis for test for the presence
of chloride ions bromide ions or iodine ions
- Precipitate forms when silver nitrate solution is added to
solutions containing these ions
- eg.......NaCl2(aq) + AgNO3 (aq) =
NaNo3(aq) + AgCl (s)
- eg.......NaCl2(aq) + AgNO3 (aq) =
NaNo3(aq) + AgCl (s)
- Precipitate forms when silver nitrate solution is added to
solutions containing these ions
- their insolubility is basis for test for the presence
of chloride ions bromide ions or iodine ions
- halide ion
- Chloride
- Bromide
- Iodide
- Iodide
- Bromide
- Chloride
- precipitate formed
- silver chloride
- silver bromide
- silver iodide
- silver iodide
- silver bromide
- silver chloride
- colour of precipitate
- white
- cream
- yellow
- yellow
- cream
- white
- formed by halogens
- Carbonate ions
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