Testing for Cations
Edited by Jamie (ScienceAid Editor), SpellBot, Anonymous
A flame test can be used where a a compound is put under a flame. The procedure is as follows:
- 1Heat the nichrome wireAdvertisement
- 2Dip in the hydrochloric acid
- 3Dip wire into compound so a small blob is collected on the wire
- 4Put under a flame and see what color it turns.Advertisement
These are the colours you will see for different ions:
Sodium Hydroxide Test for Cations
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.
|Cation||Precipitate color||Further results|
|Aluminium (Al3+)||White||Precipitate dissolves as more NaOH is added to the solution|
|Calcium (Ca2+)||White||Precipitate will not dissolve in the NaOH solution|
|Copper (Cu2+)||Pale blue||none|
|Iron(II) (Fe2+)||Pale green||none|
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.
- If you have problems with any of these steps, ask a question for more help, or post in the comments section below.
Categories : Applied
Recent edits by: SpellBot, Jamie (ScienceAid Editor)