Basics
Periodic Table
Industrial
Organic Chem.

Analytic
Analysing Gases
Quantative Chemistry
Solubility of Salts
Testing for Anions
Testing for Cations
Titration

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.