2.1 qualitative chem -Hints for the internal

Hints for your internal
1. Write down EVERY test you do on each unknown

2. Write an ionic equation foe EVERY precipitate that you form and EVERY complex ion that you form.

3. If you are not sure about the state symbols [(s), (aq)] then leave them out of your equations.


Odd bits and pieces.
1. Reactions in your internal that do not follow the rules.

When you react silver ions (Ag+) with sodium hydroxide (NaOH) a brown precipitate of silver oxide is formed instead of the expected silver hydroxide.
2Ag+(aq) + 2OH-(aq) --> Ag2O(s) + H2O.

2.Other odd bits:

When you are identifying chloride ions in a solution of copper chloride CuCl2.
The addition of silver nitrate to identify the Cl- ions forms a white ppt of silver chloride.
Ag+(aq) + Cl-(aq) --> AgCl(s)

When ammonia is added to this white ppt of silver chloride the ppt will disappear, BUT
The addition of ammonia will also result in the formation of the following ppt:
Cu2+ + OH- --> Cu(OH)2 (light blue ppt)

So the ppt of silver chloride disappears and the silver complex ion [Ag(NH3)2]+(aq) is formed. But a light blue ppt of Cu(OH)2(s) remains.

You will observe a white ppt turning from white AgCl to light blue Cu(OH)2.


3. When your add potassium thiocynate to iron (III) ions, a complex ion is formed that is blood red in colour.
Fe3+(aq) + SCN-(aq) --> [Fe(SCN)]2+ (aq).

4. A confirming test for I-(aq) ions
If you are unsure if you have Cl- or I- ions, then you can check by adding lead ions (Pb2+)
If you have I- ions then you will get a bright yellow ppt of PbI2(S)