College of Staten Island Chemistry Quantitative Analysis Report

Qualatative Analysis: Group I ions
The directions and results for the analysis of the Group I cations can be summarized in a flow
diagram. The general format of a flow diagram begins with listing of all the possible ions including
charges at the top of the diagram. Within the diagram, vertical lines link successive steps in the
procedure. For each vertical line, the reactant cations or substances are at the top of end of each
line and the products are formed at the bottom end of each line. On the product end, a horizontal
line separates the solid products (left side) from the solution products (right side). On the right
side, ions in solution will be described as ions including charges where as on the left side, a
precipitate will be described as the solid formed (e.g. AgCl not Ag+). Reagents and conditions that
are used to carry out each step are placed alongside the vertical lines.
Finish the partially completed flow diagram for the Group I ions below. One can use this diagram
to serve as a brief guide to the procedure as well as it can be used directly record your observations
for your known solution.
Group I Flow Chart
Ag+ and Pb 2+
Add 6 M HCl
White precipitate
AgCl, PbCl2
Solution contains
other ions
Heat
White precipitate
AgCl
Solution contains____________
Solution contains____________
_____________
indicates the presence of ________
_____________
indicates the presence of ________
Qualatative Analysis: Group II ions
Qualatative Analysis: Group III ions
Post-Laboratory Exercises (32 points)
1. (0 points) A known solution contains Pb2+, Hg22+, and Ag+ ions. The chlorides of Pb2+, Hg2 2+
Ag+ are all insoluble in cold water. Lead(II) chloride is separated from silver chloride and
mercury(I) chloride by heating with water. The other two insoluble chlorides, AgCl, and
Hg2Cl2, can be separated each other by adding aqueous ammonia. The solid (AgCl) dissolves
by the addition of aqueous ammonia to afford the complex ion Ag(NH3)22+. Through an
oxidation-reduction reaction, ammonia reacts with Hg2Cl2 to afford finely divided elemental
mercury that is black and the compound HgNH2Cl that is white.
Hg2Cl2 (s) + 2 NH3 (aq) ® Hg (l) + HgNH2Cl (s) + NH4 + (aq) + Cl- (aq)
Black
White
Finish the partially completed flow diagram below.
Group I Flow Chart
Ag+, Hg22+, Pb 2+
Add 6 M HCl
White precipitate
AgCl, Hg2Cl2, PbCl2
White precipitate
AgCl, Hg2Cl2
Solution contains
other ions
Solution contains____________
Add NH3 (aq)
_____________
_____________
indicates ________
Solution contains____________
_____________
indicates ________
indicates ________
2. (3 points) A solution may contain Pb2+, Hg22+, and Ag+ ions. A white precipitate formed upon
the addition of 6 M HCl. This solid was heated for 10 minutes. After which, the solution was
decanted from the solid. No further tests were conducted on the decanted solution. The solid
turned black upon the addition of 6 M NH3. Acidification of this solution with nitric acid did
not reform a white precipitate. Which ions are present, which are absent, or which may remain
undetermined? Indicate if any test(s) are needed to verify the presence of the undetermined
ion.
Present:__________________
Absent:__________________
Yet to be determined:____________ Test needed to verify:____________________
3. (3 points) A solution may contain Pb2+, Hg22+, and Ag+ ions. A white precipitate formed upon
the addition of 6 M HCl solution. Some of the white precipitate dissolved in hot water. The
solution was decanted from the remaining white solid A. The addition of ammonium carbonate
to the decanted solution afforded a white precipitate B. The white solid A was then treated with
6 M NH3 in which afforded a black solid. Which ions are present, which are absent, or which
may remain undetermined? Indicate if any test(s) are needed to verify the presence of the
undetermined ion.
Present:__________________
Absent:__________________
Yet to be determined:____________ Test needed to verify:____________________
4. (3 points)A solution may contain Pb2+, Hg22+, and Ag+ ions. A white precipitate formed upon
the addition of 6 M HCl solution. After heating, the solution was decanted from solid A. The
addition of ammonium carbonate to the decanted solution afforded a precipitate B. Solid A
was then treated with 6 M NH3 that yielded a colorless solution with no observed solid. Which
ions are present, which are absent, or which may remain undetermined? Indicate the test(s)
needed to verify the presence of the undetermined ion.
Present:__________________
Absent:__________________
Yet to be determined:____________ Test needed to verify:____________________
5. (5 points) A solution may contain Ag+, Pb2+, Al3+, Fe3+, and Mn2+ ions. Upon addition of 6 M
HCl, a white precipitate formed (solid A). The solution, which contained the group II ions, was
separated from solid A which in a later step completely dissolved in a hot water bath. This
homogeneous solution was then treated with ammonium carbonate to afford an insoluble
carbonate.
The group II ion solution was made slightly basic to yield a precipitate (solid B). After
decanting, 6 M NaOH was added to the solution until strongly basic in which some of solid B
dissolved. The resulting solution was then decanted from solid B. Phosphoric acid was added
to this solution that produced a white precipitate. Solid B dissolved upon treatment with nitric
acid to form solution C that was then divided between two test tubes. Solution C turned a
reddish-purple in the presence of NaBiO3 but there was no visible reaction in the presence of
KSCN. Which ion(s) are present and which are absent?
Present:__________________
Absent:__________________
Yet to be determined:__________ Test needed to verify:____________________
6. (5 points)A solution may contain Ag+, Pb2+, Al3+, Fe3+, and Mn2+ ions. Upon addition of 6 M
HCl, no precipitate formed. However, a precipitate (solid B) formed after the solution was
made slightly basic. After decanting, 6 M NaOH was added to the solution until strongly basic
that resulted in a fraction of solid B dissolving. The resulting solution was then decanted from
solid B. This solution was made slightly acidic that yielded a white precipitate. Solid B
dissolved upon treatment with nitric acid to form solution C that was then divided between
two test tubes. Solution C turned a dark red in the presence of KSCN. Which ion(s) are present,
which are absent, or which may remain undetermined? Indicate if any test(s) are needed to
verify the presence of the undetermined ion.
Present:__________________
Absent:__________________
Yet to be determined:__________ Test needed to verify:____________________
7. (5 points) A solution may contain Ag+, Pb2+, Al3+, Fe3+, and Mn2+ ions. Upon addition of 6 M
HCl, a white precipitate formed (solid A). The solution, which contained the group II ions, was
separated from solid A which in a later step was placed in a hot water bath. The solution was
decanted from the insoluble chloride. The silver chloride formed a soluble complex ion with
the addition of aqueous ammonia, then precipitated again upon the addition of nitric acid.
The group II ion solution was made slightly basic to yield a precipitate (solid B). Solid B
dissolved upon treatment with nitric acid to form solution C that was then divided between
two test tubes. Solution C turned a reddish-purple in the presence of NaBiO3 while the addition
of KSCN afforded a dark red color in the other test tube. Which ion(s) are present, which are
absent, or which may remain undetermined? Indicate if any test(s) are needed to verify the
presence of the undetermined ion.
Present:__________________
Absent:__________________
Yet to be determined:__________ Test needed to verify:____________________
8. (8 points) The unknown solution below may contain the following ions: Ag+, Pb2+, Al3+, Fe3+,
Mn2+, Mg2+, Co2+, Cu2+, Ni2+, NH4+.
Upon addition of 6 M HCl, a white precipitate formed (solid A). The solution, which contained
the group II ions, was separated from solid A. The solution II, which contains the group II
ions, was decanted from a white precipitate. This white solid did not dissolve in the hot water
bath but the solid did dissolve in aqueous ammonia. The same white precipitate was formed
after adding nitric acid. The addition of ammonium carbonate to the decanted solution did not
result in a precipitate despite the solution being basic.
The group II ion solution (solution II) was made slightly basic to yield a precipitate (solid C).
After decanting solid C from solution III, 6 M NaOH was added to solid C until strongly basic
in which some of solid C dissolved. The resulting solution was then decanted from solid C.
Phosphoric acid was added to this solution that produced a white precipitate. Solid C dissolved
upon treatment with nitric acid to form solution D that was then divided between two test tubes.
Solution D turned a reddish-purple in the presence of NaBiO3 but there was no visible reaction
in the presence of KSCN.
Treatment of solution III with a 1 M Na2HPO4 solution yielded a white precipitate that was
decanted from solution III. After heating to dryness, the resulting residue was acidified and
then the solution was partitioned between four small test tubes. To the first test tube, a spatula
tip of KI was added to produce a tan solid/brown liquid. In the second test tube, no change was
visible with the addition of a few drops of the DMG solution. To the third test tube, 1 mL of
the NN solution was added to the solution that resulted in the formation of a red-brown
precipitate. The contents of the fourth test tube were added to a hot NaOH solution that gave a
positive test for the ammonium ion.
Present:______________________________________________________________
A possible false positive:____________