One Point Quiz

1
One Point Quiz

• One quiz per table, list everyones name
• Agree on an answer
• You have two minutes

2
Did You Know?
Problem Set Answers are posted outside the
Chemistry Laboratory in a glass case
3
Problem Set Iron and Barium
4
Sulfide Precipitation

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

5
Soluble Sulfides
6
Insoluble Sulfides
7
Preparation of Hydrogen Sulfide(acidic solution)
An aqueous solution H2S of is called
hydrosulfuric acid
thioacetamide
8
Preparation of Sulfide Ion(basic solution)
0.1 M Na2S S2 5.0 x 102 M
0.1 M (NH4)2S S2 2.0 x 105 M
Write the reaction of aqueous ammonia and
hydrosulfuric acid to give sulfide ion.
9
Reactions of Hydrosulfuric Acid(polyprotic acid)
hydrosulfuric acid.
bisulfide ion
sulfide ion
10
First Dissociation of H2S
Also called Ka,1
11
Second Dissociation of H2S
12
Double Dissociation of H2S
K1?K2
1.3 x 1020 M2
This equilibrium constant can be used for any
sulfide ion and pH calculation at room temperature
13
Dissociation of Hydrosulfuric Acid
The solubility of H2S in water decreases with
increasing temperature.
The amount of sulfide ion in solution is pH
dependent.
14
Thioacetamide is heated in boiling water for 5
minutes
H2S 0.10 M
Determine the concentration of the other sulfur
containing species
15
The Effect of pH on the Sulfide Ion Concentration
16
What would a graph of the various sulfide
containing species versus pH look like?
S2
HS
H2S
acidic
basic
Excel
Graph
17
Graph
18
(No Transcript)
19
0.10 M Silver Ion Solution
What sulfide ion concentration is needed to
precipitate silver sulfide?
If the concentration of H2S in the aqueous
solution is 0.10 M, what will be the pH of the
solution when silver sulfide begins to
precipitate?
20
0.10 M Silver Ion Solution
Ag2 S2 Ksp
S2

21
0.10 M Silver Ion Solution
S2 6.8 x 1048 M
0.10 M
Remember this equilibrium constant? It can be
used for any sulfide ion and pH calculation
pH -13.1
22
An aqueous solution contains 0.1 M concentrations
of the following ions
Ag, Cd2, Co2, Cu2, Fe2, Mn2, Ni2, Pb2
In what order will these ions precipitate when
sulfide is added to the solution?
If the H2S concentration is 0.10 M, at what pH
will each ion begin to precipitate?
Select a 2 metal ion (0.1 M) and calculate the
pH at which the metal sulfide of that ion will
begin to precipitate.
23
Sulfide Precipitation Values
24
One Point Quiz

• One quiz per table, list everyones name
• Agree on an answer
• You have two minutes

25
Problem Set Sulfide Precipitation Reactions
26
Selective Precipitation
27
Sulfide Ion Precipitation
A solution has the following composition 10 drops
0.10 M Ni2 10 drops 0.10 M Pb2 2 drops 0.10 M
Cu2 6 drops thioacetamide 2 drops 6 M HCl 20
drops water
What is the concentration of each cation?
28
Sulfide Ion Precipitation

• 10 drops 0.10 M Ni2
• 10 drops 0.10 M Pb2
• 2 drops 0.10 M Cu2
• 6 drops thioacetamide
• 2 drops 6 M HCl
• 20 drops water
• 50 drops total volume

29
Cation Concentrations
Ni2
x 0.10 M
0.020 M
Pb2
x 0.10 M 0.020 M
Cu2
x 0.10 M 0.004 M
H
x 6.0 M 0.24 M
30
Sulfide Ion Generation
The solution is boiled for 5 minutes to generate
a saturated H2S solution.
What is the concentration of sulfide ion in this
solution, if H 0.24 M?
31
Sulfide Ion Generation
H2S
0.10 M
K12 1.3 x 1020 M2
32
Sulfide Ion Generation
H2S 0.10 M
H 0.24 M
S2 2.3 x 1020 M
33
Which of the metal ions remain in solution and
which precipitate?
34
Which of the metal ions remain in solution and
which precipitate?
NiS
Ni2 S2
(0.020)(2.3 x 1020)
4.6 x 1022 M2
This is what we have
Ksp, NiS 3.0 x 1021 M2
This is the solubility limit
Determine if lead(II) ion will precipitate or
remain in solution.
35
Which of the metal ions remain in solution and
which precipitate?
PbS
Pb2 S2
(0.020)(2.3 x 1020)
4.6 x 1022 M2
Ksp, PbS 4.2 x 1028 M2
lt 4.6 x 1022 M2
Determine if copper(II) ion will precipitate or
remain in solution.
36
Which of the metal ions remain in solution and
which precipitate?
CuS
Cu2 S2
(0.004)(2.3 x 1020)
9 x 1023 M2
Ksp, CuS 8.7 x 1036 M2
lt 9 x 1023 M2
37
Which of the metal ions remain in solution and
which precipitate?
38
Metal Sulfide Dissolution Reactions

• Sulfuric Acid

• The acidity of the solution will determine if the
  metal sulfide will dissolve.

• Sulfate ion is a poor coordinating ligand, and
  does not assist in the dissolution process.
• Hydrogen sulfide gas is released if the metal
  sulfide dissolves.

FeS(s) 2 H(aq)
Fe2(aq) H2S(g)
39
Metal Sulfide Dissolution Reactions

• Hydrochloric Acid

• HCl will dissolve a few metal sulfides that
  sulfuric acid does not dissolve.

• Chloride ion coordinates to the metal ion to form
  a more soluble complex anion.
• Hydrogen sulfide gas is released if the metal
  sulfide dissolves.

40
Metal Sulfide Dissolution Reactions

• Hydrochloric Acid

CdS(s) 2 H(aq) 4 Cl(aq)
CdCl42 H2S(g)
?
tetrachlorocadmate ion
Cadmium sulfide will not dissolve in 6 M sulfuric
acid but will dissolve in 6 M hydrochloric acid
41
Metal Sulfide Dissolution Reactions

• Nitric Acid

• All metal sulfides dissolve in warm nitric acid.

• The nitrate ion is an oxidizing agent which
  oxidizes sulfide ion (S2 ) to white elemental
  sulfur (S).
• During the redox process, nitrate ion is reduced
  to NO2 gas, or in the case of nickel to NO gas.

42
Metal Sulfide Dissolution ReactionsNitric Acid
2 Ag(aq)
S(s)
2 e
NO3(aq)
NO2(g)
2 H(aq)
e
H2O(l)
2
2
4
2
2
4 2
Ag(aq) NO2(g) H2O(l) S(s)
2 2 2
Balance this redox equation in acidic solution
43
End of Part 1
Be sure to review the Exam I Objective Sheet
44
(No Transcript)
45
The organization of the elements by Moseley is
accepted as being superior to that of the Meyer
and Mendeleev.In which of the following ways is
it the most superior?
Prediction of missing elements
Prediction of elemental properties
Prediction of compounds formed with
hydrogen and oxygen
46
Write a balanced and completely annotated
(g,s,l,aq) chemical net ionic equation for the
reaction of diamminesilver ion with hydrochloric
acid to give insoluble silver chloride.
Ag(NH3)2 2 H(aq) Cl(aq)
AgCl(s) 2 NH4(aq)
47
Which of the following is the most basic?
Next
48
An aqueous solution contains0.1 M Cd2 and 0.1 M
Cu2
Ksp
Cd(OH)2
Cu(OH)2
Cu(OH)2
If the solution is slowly made basic, what will
be the formula of the first precipitate to form?
Next
49
(No Transcript)
50
One Point Quiz

• One quiz per table, list everyones name
• Agree on an answer
• You have two minutes