The document provides instructions for qualitative analysis to identify cations like Pb2+, Hg2+, and Ag+. It describes separating these group I cations from solution by adding HCl to precipitate them as chlorides. Lead chloride can then be separated from AgCl and Hg2Cl2 by heating with water. Hg2Cl2 can be identified by its reaction with ammonia, forming metallic mercury and aminomercuric chloride. Silver chloride is also soluble in ammonia but will re-precipitate upon addition of acid.

2. Separate /save some unknown
• DR ROB’S “Get to the point of this lab!”
• Worksheet
• Postive cations like Pb2+ , Ag + and Hg+
• Can be ptt by OH-, Cr2O72-, S2-
• And Cl-

3. Pb2+ Cr2O72-

4. .
• The most confusing ion is the S2- ion
• In acidic and in basic solutiopn
• Chemlab sheet
• Centiguge sheet

5. Best website
• http://www.dartmouth.edu/~chemlab/chem3
-5/qual_cat/full_text/procedure.html

6. .
• FROM BOOK RIGHT TO ADEMDUM
• MENTION 12 IONS
• YOU WILL DO THREE TODAY
• DO ADDEMDUM FIRST
• THEN GO TO BOOK
• REVIEW CENTRIFUGE

7. .
• EASY FOR SOMETHING TO OCCUR DURING
THESE LABS
• MUST PLAN BEFORE YOU GET HERE
• USE OR LAB BOOK TO WRITE DOWN
REACTIONS-MANY TESTSTUBES ALL AT
ONCE!

8. .
#1 – Qualitative Analysis
• Principles of Qualitative Analysis
1.Confirmatory Tests:
These are tests that determine conclusively that
a certain ion is present. Interfering ions are
removed before a confirmatory test is done.
• .

9. .
Separations:
These are procedures that separate groups of
ions from other groups, or individual ions in a
mixture of ions. Separations are followed by
confirmatory tests to identify the separated
ion.

10. Precipitation and Separation of Group
I Cations:
• Group 1: The silver group: Ag+, Hg22+,
Pb2+ -----These ions precipitate (as the
chlorides) from 0.3M HCl solution.
• « » »Rationale: Softest acids>>>>>>>>
• react strongly enough with a borderline base
• to precipitate in acid solution..

11. You know some of this already
• You have already done lead in CHM121
• And,
• You have just done another ion similar to Ni–
which will get to shorty (Cu(NH3)4)

12. Just add hot water
These cations are Pb+2, Hg2
• +2, and Ag+ are all insoluble in cold water.

13. Precipitation and Separation of Group
I Cations:
• Precipitation and Separation of Group I
Cations:
• Pb+2, Hg2+2, and Ag+ are all insoluble in cold
water.
• They can be removed as a group from
solution by the addition of HCl via simple
precipitation:
Ag+ + Cl- → AgCl(s)

14. chloro-complexes may form !!
• It is important to add enough HCl to ensure
complete precipitation, but not too large an
excess. In highly concentrated HCl solutions,
chloro-complexes may form such as
• AgCl2-1.

15. Precipitation and Separation of Group
I Cations:
• Lead chloride can be separated from AgCl
and Hg2Cl2 by heating with water, essentially
reversing the above reaction.
• Once Pb+2 is in solution, you can discern its
presence by adding chromate ion to produce a
yellow solid:
• Pb+2 + CrO4-2 → PbCrO4(s) (yellow)

16. Begin . . . . . .
• Show the PDF
• Show the word files
• Show flow chart now

17. Precipitation and Separation of Group
I Cations:
• Hg2Cl2 can be distinguished from AgCl by
reaction with ammonia via oxidation
reduction to yield finely divided black
metallic mercury and a white complex
compound HgNH2Cl. As the reaction
proceeds, the solid appears to change colors
from white to black or gray:

18. .
• Hg2Cl2(white solid) + 2 NH3(aq)
→
• NH4+(aq) + Cl-(aq) + Hg(black
liquid) + HgNH2Cl(white solid)

19. Hg2Cl2(white solid) + 2 NH3(aq) →
NH4+(aq) + Cl-(aq) + Hg(black liquid) +
HgNH2Cl(white solid)

20. Aminomercuric chloride
and,

21. • Silver chloride also reacts with aqueous
ammonia to form a complex ion that remains
in solution. Addition of a
• strong acid will destroy the complex and
confirm the presence of silver ion by re-
precipitating the white AgCl solid:

22. • Silver chloride also reacts with aqueous ammonia to form a complex ion that remains in
solution. Addition of a
• strong acid will destroy the complex and confirm the presence of silver ion by re-precipitatin
the white AgCl solid:
• AgCl(s) + 2 NH3(aq) → Ag(NH3)2 +(aq) + Cl-(aq)
• Ag(NH3)2+(aq) + 2 H+(aq)+ Cl-(aq) → AgCl(s) + 2 NH4aq)