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Identification of ions and gases - Coggle Diagram
Identification of ions and gases
Identification of cation
Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide and ammonia
Metal cation:
Aluminum(Al3+)
Ammonium(NH4 +)
Chromium(lll)(Cr3+)
Copper(III)(Cu3+)
light blue precipitate insoluble in excess
EFFECT OF ADDING
NaOH
white precipitate is formed and dissolve in excess to create a colorless solution
white precipitate is formed and is insoluble in excess solution
ammonia gas is formed if heated
green precipitate is formed and form a green solution in excess
pale green precipitate is formed and insoluble in excess
2 more items...
grey green precipitate and insoluble in excess
1 more item...
do not have reaction
very faint white precipitate is formed
white precipitate is formed and insoluble in excess
light blue precipitate is formed and dark blue solution is formed in excess
EFFECTS OF ADDING AMMONIA SOLUTION
Calcium(Ca2+)
iron(II)(Fe2+)
iron(III)(Fe3+)
zinc(Zn2+)
lead(pb2+)
white precipitate is formed and produce colorless solution in excess
Identification of anions
Common methods
Precipitation reactions
With silver nitrate (AgNO3)
Br⁻: Cream precipitate (partly soluble in NH3)
I⁻: Yellow precipitate (insoluble in NH3)
Cl⁻: White precipitate (soluble in NH3)
With barium chloride (BaCl2)
SO4²⁻ = White precipitate (insoluble in dilute HCl)
Identification of gases
Gas test
Carbon dioxide
Add acid, releases CO2 gas (turns limewater milky).
Sulfur dioxide
Add acid, releases SO₂ gas (smells like burning sulfur).
Nitrate
add a dilute aqueous sodium hydroxide , if ammonia is given off the substance contains nitrate ions
chloride ion
Add silver nitrate (AgNO3) solution, which forms a white precipitate of silver chloride (AgCl).
hydroxide ion
When hydrogen ions react with hydroxide ions, they form water (H2O). If a solution contains an excess of hydrogen ions, it's acidic and usually lacks hydroxide ions. Conversely, if a solution contains hydroxide ions in excess, it's basic (alkaline) and usually lacks hydrogen ions.
oxygen
Collect the gas in a tube and hold a glowing splint near it.
Flame test
Colors of flames
Lithium = red
Sodium Ion = yellow
Potassium = lilac
Calcium = orange-red
Barium = light green
Copper(ii) = blue-green