Aluminium
The Blast Furnace
Purification of Copper
Crude Oil
Electrolysis
Analysing Gases
Haber Process
Solubility of Salts
Steel
Test for Anions
Test for Cations
Titration

Other Section

Applied
Fundamental
Inorganic
Organic
Physical

Testing for Cations

Flame Test

A flame test can be used where a a compound is put under a flame. The procedure is as follows:

  • Heat the nichrome wire
  • Dip in the hydrochloric acid
  • Dip wire into compound so a small blob is collected on the wire
  • Put under a flame and see what colour it turns.

    • how to carry put the flame test

    These are the colours you will see for different ions...

    IonColour
    Na+Orange-yellow
    K+Lilac
    Ca2+Brick-red
    Cu2+Green

    Sodium hydroxide

  • Add several drops of sodium hydroxide (NaOH) solution to the solution being tested.

  • If a coloured precipitate is formed then stop and find out what the cation is.

  • If a white precipitate forms then continue to add NaOH to it and observe whether the precipitate dissolves.

    • AnionPrecipitate colourFurther results
    Aluminium
    Al3+    		WhitePrecipitate dissolves as more NaOH is added to the solution.
    Calcium
    Ca2+    		WhitePrecipitate will not dissolve in the NaOH solution
    Copper
    2+    		Pale bluenone
    Iron (II)
    Fe2+    		Pale greennone
    Iron (III)
    Fe3+    		Red-brownnone

    The ionic equation for these reactions are all very similar, here is an example it with Aluminium:

    Al3+ (aq) + 3OH- Al(OH)3 (s)

    All you have to do for any other ionic equations for this test is to change the number of OH- ions so that it balances with the oxidation state of the metal anion. E.g. Iron (II) would need two OH- whereas Iron(III) needs 3.