In this laboratory exercise we will separate and identify Cations dissolved in an Aqueous system. Since we will not quantify the amount of each Cation present, but instead merely discern its presence, such a scheme for separation and identification is referred to as a Qualitative Analysis. In our particular case, we will be testing for the presence of the following nine Cations: Ag+, Pb2+, Cu2+, Bi3+, Fe3+, Mn2+, Ni2+, Ba2+, Na+

1. Author : Dr Robert D. Craig
The possible cations in your unknown sample are
given in the following list, organized according
to the separation scheme. These ions should all
be familiar to you.

2. The possible cations in your unknown sample
are given in the following list, organized
according to the separation scheme. These ions
should all be familiar to you.

4.  Group I: Hg2+, Pb2+, Ag+
Group II: Cu2+ ,Bi3+ Cd 2+, and Sn4+
Group III: Fe2+, Ni2+, Mn2+

5.  Theory will be place on last few slide

6.  Lets go right top procedure
 Will place theory at end

7. Bismuth nitrate penta hydrate
Cadmium Chloride Hemipentahydrate
Copper (ii) Nitrate Hemipentahydrate
Tin (iV) chloride pentahydrat

8.  Get solution containing 4 ions
 Add h2S test pH
 Interestiglg
 SnS2 is an acid

9.  GOTO HANDOUT WITH PIC OF WHAT
YOU SHOULD SEE

10.  Adjust pH with test paper
 Today you must work a little hsarder!
 pH > 0.8
 Ph < 0.2 are NO GOOD
 Make NH3
 Make HCl

11.  pH > 0.8
 Ph < 0.2 are NO GOOD
 Make NH3
 Make HCl

12.  Get solution containing 4 ions
 Add h2S test pH
 Interestiglg
 SnS2 is an acid

13. Precipitation of Group II Sulfides
Cu2+ + S2- CuS(s)- Brown Black
Confirmation test for copper: Formation of Cu2+
ion
Cu2++ 4 NH3 (aq) Cu(NH3)42+ (aq)- Blue

14. Dangers- must make several hot water baths!!!
Can boil chemicals
Caution when diliting acids and bases-to eyes
Source of H2S is toxic!

15. III. Analyzing a Group II Unknwn Solution
***Take 4 drops of each of the four Cations to
make Group II Known Solution For testing
• Bismuth nitrate penta hydrate
• Cadmium Chloride Hemipentahydrate
• Copper (ii) Nitrate Hemipentahydrate
• Tin (iV) chloride pentahydrate

16.  Get solution containing 4 ions
 Add h2S test pH
 Interestiglg
 SnS2 is an acid

17.  Adjust pH with test paper
 Today you must work a little hsarder!
 pH > 0.8
 Ph < 0.2 are NO GOOD
 Make NH3
 Make HCl

18.  pH > 0.8
 Ph < 0.2 are NO GOOD
 Make NH3
 Make HCl

19. When you Take 4 drops of each of the four
Cations to make Group II Known Solution For
testing-need to do the following
1 drop of 6M HCl + 11 drops of H2O -> 0.5 M
HCl
1 drop of 6M NH3 + 11 drops of H2O -> 0.5 M
NH3
Use Short Range Alkacid (blue green) paper to
adjust pH 0.5

20. 2. Part B : Add HCl until solution is 0.5 pH
with short range Alkacid paper instead of
litmus
3. Part D: Use Wide Range Alkacid (orange)
paper to determine if solution is strongly
basic

21. 4. Part B: Confirmation of Tin (IV)
SnS2 is a yellow precipitate A white solid does
not indicate present of Tin
DO NOT STOPPER the tube before heating

22.  SnS2 is a yellow precipitate
 YOU MUST DROP ALL 4 CATIONS FIRST –
AS SULFIDES—THEN ADD NaOH
 This will make Sn(OH)6-
 It is amphoteric!!!!!

23.  Go right to page 143 and your flow chart
 And goto data sheet 1 in blue book
 This is it rob!!!!

24.
Here is what we will look for !!!!!!
And, Let us review the concept of the
Ion product-Table 3 page 111 (video in
blackboard)
Ni 2+ , Fe2+ Cr 3+

28.  Pb2+ + CrO42- PbCrO4 (s)
 See adendum:
 CrO4- is Yellow-add acid
 CrO5 – is dark blue
 Cr(OH)3- is blue Green

29.  You will not see these pictures yet
 The three ions above separate out very easily
and at a low conc
 Of S2-

30.  Table 2 reveals that precipitating the 0.1 M
cations iron (II) (Fe2+, ferrous) and nickel (II)
(Ni2+, nickelous) as sulfides requires a S2- ion
concentration that is at least 1 x 10 6 times
larger than that required for precipitating Bi 3+
, Cu 2+ , Cd 2+ and Sn 4+ ions as their
respective sulfides

31. Thus, the precipitation of NiS and iron (II) sulfide
(FeS, ferrous sulfide) with their larger solubility
product constant can be avoided if the S 2- ion
concentration is
maintained below 1.8 x 10 -20 M

32. A Selected group of chemically important and
commonly encountered cations appear in table I
• *Please see this in lab manual
Of these cations, the group I cations
Ag+, Hg2+ , and Pb 2+ ions, may be removed from
solution by precipitating as chlorides
This is due the “ion product” for these ions-on the
Ksp

33. For instance
Ksp = [Pb2+][CRO4 2-] =
The group ii cations Bi3+ , Cu 2+ , Cd 2+ and Sn
4+
Form insoluble sulfide precipitates even at very
low sulfide ion (S 2-) concentrations.