1. The insoluble Chlorides AgCl, Hg2Cl2, PbCl2
Type I Cations
The insoluble Chlorides
AgCl, Hg2Cl2, PbCl2

2. The only metals to make insoluble chlorides
Formula Ksp
AgCl x 10-10
Hg2Cl x 10-19
PbCl x 10-5
Make the chlorides by reacting with Ag+, Hg22+ and Pb2+ with HCl
If you don’t add too much HCl they all precipitate out of solution they are all white solids
If you add too much HCl then the PbCl2 and AgCl dissolve
PbCl2(s) + 2Cl-(aq)  [PbCl42-](aq)
AgCl(s) + Cl-(aq)  [AgCl2-](aq)
Once we have these as the metal chlorides we need a way to identify which of the metals are present, is it just one or all of them?

3. Separate the Pb and Confirm
Of the chlorides PbCl2 has the largest Ksp – in hot water some of the PbCl2 dissolves (PbCl2 has a 3-fold increase in solubility from 20—100oC while the AgCl and the Hg2Cl2 stay as solids) PbCl2(s) → Pb2+(aq) + 2 Cl-(aq) Separate by centrifuging. To the supernatant add Lead(II)Chromate Pb2+(aq) + CrO42-(aq) → PbCrO4(s, yellow) A yellow PPT confirms Pb2+

4. Separate Ag+ from Hg22+
To the PPT from the first step, add 10 drops of 4M or 6M NH4OH AgCl(s) will dissolve in NH3(aq) AgCl(s) + 2 NH3(aq) → [Ag(NH3)2+](aq) + Cl-(aq) meanwhile the mercurous chloride, disproportionates Hg2Cl2 (s) (white) + 2NH3(aq) → Hg(s, black) + HgNH2Cl (s, white) + NH4Cl(aq) A black/white/grey PPT confirms the presence of the mercurous cation

5. Confirm Ag To the solution (supernatant) add 6M HNO3 till acidic
Ag(NH3)2+(aq) + 2H+(aq) → Ag+(aq) + 2 NH4+(aq)
Ag+(aq) + Cl-(aq) → AgCl(s)
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Ag(NH3)2+(aq) + 2 H+(aq) + Cl-(aq) → AgCl(s, white) + 2 NH4+(aq)
White PPT of AgCl(s) confirms Ag+

6. Flow Diagram Ag+(aq), Hg22+(aq), Pb2+(aq) HCl
AgCl(s,white), Hg2Cl2(s, white), PbCl2(s, white)
Hot water
Pb2+(aq)
AgCl(s,white), Hg2Cl2(s, white)
NH3(aq)
K2CrO4(aq)
PbCrO4(s, yellow)
Ag(NH3)2+(aq)
Hg(s, black), HgNH2Cl (s, white)
Yellow ppt confirms Pb2+
Grey ppt confirms Hg22+
HNO3(aq)
AgCl (s, white)
White ppt confirms Ag+

7. Technique Tips
Cleanliness is VITAL use clean test tubes, stirring rods etc
Dispense from clean droppers, or the droppers that are reserved for that particular reagent
Do not place the tip of the dropper into the solution in the test tube
Always screw the cap back on the reagent bottle after use
Mixing of a reaction mixture:
Small amounts in the bottom of the test tube can be mixed by flicking the bottom of the test tube
Larger amounts stir with a clean glass stirring rod
Use small test tubes for centrifuging and always ensure there is a test tube in the slot opposite the one you are using otherwise the centrifuge is unbalanced
After centrifuging carefully pour off the liquid (decantate or supernatant) into a clean test tube
Wash the precipitate with deionized water so that subsequent chemical tests are not interfered with by contaminants
Heat test tubes in a water bath
Test pH by placing the wet stirring rod on the pH paper (do not put the pH paper in the test tube)

8. Today and Monday Work individually
Run the known along with your unknown
Record observations of each step
Use your observations to determine what you have in the unknown
Check with me
Bottle beer?