9 - Tests for Cations & Anions Flashcards
What colour flame does a Lithium ion give?
Crimson / Red
What colour flame does a Sodium ion give?
Yellow
What colour flame does a Potassium ion give?
Lilac
What colour flame does a Calcium ion give?
Orange-Red
What colour flame does a Copper ion give?
Blue-Green
How do you carry out a flame test?
- Clean a nichrome wire loop in hydrochloric acid & rinse in distilled water
- Dip wire loop into sample of the metal compound & put wire into hottest bunsen burner flame
- Record the colour of the flame
How can you use NaOH to test for metal ions?
- Add a few drops of sodium hydroxide to a solution of mystery compound
- If a hydroxide precipitate forms, you can use the colour to tell what metal ion was in the compound
What colour precipitate is Aluminium?
White - then redissolves in excess NaOH to form colourless solution
What colour precipitate is Calcium?
White
What colour precipitate is Copper(II)?
Blue
What colour precipitate is Iron(II)?
Green
What colour precipitate is Iron(III)?
Brown
How do you work out if a solution contains Ammonium ions (NH₄⁺)?
Add Sodium Hydroxide solution to unknown solution & gently heat
If ammonia gas is given off, ammonium ions are present
How do you test for Ammonia Gas?
Hold damp litmus paper over it, it will turn blue if ammonia gas (also has a strong smell, however ammonia is toxic at high concs)
How do you test for Halide Ions with Silver Nitrate Solution?
Add dilute nitric acid followed by a few drops of AgNO3
Why is nitric acid added when testing for Halide Ions?
Nitric acid is added to get rid of carbonate ions (which can also form a white precipitate) so the results aren’t confusing
What colour precipitate do Chloride ions form when silver nitrate is added?
White of Silver Chloride
What colour precipitate do Bromide ions form when silver nitrate is added?
Cream of Silver Bromide
What colour precipitate do Iodide ions form when silver nitrate is added?
Yellow of Silver Iodide
How do you test for Carbonate Ions (CO₃²⁻)?
Add Dilute Acid to solution
If carbonate ions present, effervescence as carbon dioxide is produced
(Can check if gas is CO2 by bubbling through limewater - it’ll turn milky)
How do you test for Sulfate Ions (SO₄²-)?
Add Dilute Hydrochloric Acid to sample - stops any precipitation reactions not involving sulfate ions happening
Add Barium Chloride Solution - white precipitate of it will form if SO₄²- present
