Tuesday, February 16, 2010

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.
Ag+(aq) + OH-(aq) --> Ag2O(s).

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. Left out bits from your notes:
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)

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