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04/18/23
One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
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Problem Set Answersare posted
outside the Chemistry Laboratoryin a glass case
Problem Set
Iron and Barium
Sulfide PrecipitationEdward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/18/23
Soluble Sulfides
Na2S 15.4 (10 °C) 1.97 M
(NH4)2S very soluble
5460 m H2S 18600 (40 °C)0.34 (100 °C) 0.10 M
g/100 g H2Omolar
solubility
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Insoluble Sulfides
Ag2SCdSCoSCuSFeSMnSNiSPbS
g/100 g H2O
6.4 x 10-16
1.4 x 10-13
2.0 x 10-10
2.8 x 10-16
1.9 x 10-8
6.2 x 10-7
5.0 x 10-10
4.9 x 10-13
molarsolubility
2.6 x 10-17
1.0 x 10-14
2.2 x 10-11
2.9 x 10-18
2.2 x 10-9
7.1 x 10-8
5.5 x 10-11
2.0 x 10-14
Ksp
6.8 x 10-50
1.0 x 10-28
5.0 x 10-22
8.7 x 10-36
4.9 x 10-18
5.1 x 10-15
3.0 x 10-21
4.2 x 10-28
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Preparation of Hydrogen Sulfide(acidic solution)
2 H+(aq) + S2–(aq) H2S(aq)
HH
CH
H
H
C N
S
+ H2O(l) H2S(aq)
thioacetamideAn aqueous solution H2S ofis called hydrosulfuric acid
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Preparation of Sulfide Ion(basic solution)
H2S(aq) + 2 OH–(aq) S2–(aq) + 2 H2O(l)
0.1 M Na2S [S2–] = 5.0 x 10–2 M
0.1 M (NH4)2S [S2–] = 2.0 x 10–5 M
Write the reaction of aqueous ammonia and hydrosulfuric acid to give sulfide ion.
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Reactions of Hydrosulfuric Acid(polyprotic acid)
2 H+(aq) + S2–(aq) H2S(aq)
H+(aq) + HS–(aq) H2S(aq)
H+(aq) + S2–(aq) HS–(aq)
hydrosulfuric acid. bisulfide ion
sulfide ion
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First Dissociation of H2S
H+(aq) + HS–(aq) H2S(aq)
[H+] [HS–]
[H2S]= K1 = 1.0 x 10–7 M
1 indicates it is theionization of the
first hydrogen ionAlso called Ka,1
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H+(aq) + S2–(aq) HS–(aq)
Second Dissociation of H2S
[H+] [S2–]
[HS–]= K2 = 1.3 x 10–13 M
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2 H+(aq) + S2–(aq) H2S(aq)
Double Dissociation of H2S
[H+]2 [S2–]
[H2S]= K12 = K1K2 =1.3 x 10–20 M2
This equilibrium constantcan be used for any sulfide ion
and pH calculation at room temperature
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Dissociation of Hydrosulfuric Acid
H+(aq) + HS–(aq) H2S(aq) 2 H+(aq) + S2–(aq)
very acidic neutral very basic
The solubility of H2S in water decreaseswith increasing temperature.
The amount of sulfide ion in solution ispH dependent.
Thioacetamide is heated in boiling water for 5 minutes
Determine the concentrationof the other sulfur containing species
[H2S] = 0.10 M
pH = 1.0 pH = 5.0 pH = 9.0
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The Effect of pH on the Sulfide Ion Concentration pH [H+] [S2–]
0
1
2
3
4
5
6
7
8
9
1.0 M
10–1
10–2
10–3
10–4
10–5
10–6
10–7
10–8
10–9
1.3 x 10–21 M
1.3 x 10–19
1.3 x 10–17
1.3 x 10–15
1.3 x 10–13
1.3 x 10–11
1.3 x 10–9
1.3 x 10–7
1.3 x 10–5
1.3 x 10–3
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What would a graph of the various sulfide containing species versus pH
look like?
pH
Mol
e F
ract
ion
acidic basic
H2S
HS–
S2–
ExcelGraph
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0.10 M Silver Ion Solution
If the concentration of H2S in theaqueous solution is 0.10 M,
what will be the pH of the solution whensilver sulfide begins to precipitate?
What sulfide ion concentration isneeded to precipitate silver sulfide?
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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 precipitatewhen 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 pHat which the metal sulfide of that ion
will begin to precipitate.
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Sulfide Precipitation ValuesIon
0.1 M Ag+
0.1 M Cd2+
0.1 M Co2+
0.1 M Cu2+
0.1 M Fe2+
0.1 M Mn2+
0.1 M Ni2+
0.1 M Pb2+
[S2–] Required
6.8 x 10–48 M1.0 x 10–27 M5.0 x 10–21 M8.7 x 10–35 M4.9 x 10–17 M5.1 x 10–14 M3.0 x 10–20 M4.2 x 10–27 M
[H+]
1.4 x 1013 M1.1 x 103 M5.1 x 10–1 M3.9 x 106 M5.2 x 10–3 M1.6 x 10–4 M2.1 x 10–1 M5.6 x 102 M
pH
-13.1-3.10.3
-6.62.33.80.7
-2.7
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One Point Quiz
One quiz per table, list everyone’s name Agree on an answer You have two minutes
Problem Set
Sulfide Precipitation Reactions
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Selective Precipitation14
10
6
2
pH
-2
-6
basic
neutral
acidic
veryacidic
FeS MnS
some metal sulfidescan be easily dissolved
CoS NiS
some metal sulfidesrequire concentratedacids to dissolve
CdS PbS
some metal sulfidesrequire concentratedacids and specialligands to dissolve
CuSAg2S some metal sulfideswill not dissolve, but can
only be destroyed with nitric acid
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Sulfide Ion Precipitation
A solution has the following composition10 drops 0.10 M Ni2+
10 drops 0.10 M Pb2+
2 drops 0.10 M Cu2+
6 drops thioacetamide 2 drops 6 M HCl20 drops water
What is the concentration of each cation?
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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 HCl20 drops water
50 drops total volume
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Cation Concentrations
[Ni2+] = x 0.10 M10 drops50 drops
[Pb2+] = x 0.10 M = 0.020 M10 drops50 drops
[Cu2+] = x 0.10 M = 0.004 M 2 drops50 drops
[H+] = x 6.0 M = 0.24 M 2 drops50 drops
= 0.020 M
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Sulfide Ion Generation
The solution is boiled for 5 minutesto generate a saturated H2S solution.
What is the concentration of sulfide ionin this solution, if [H+] = 0.24 M?
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Sulfide Ion Generation
[H2S] =
2 H+(aq) + S2–(aq) H2S(aq)
[H+]2 [S2–]
[H2S]= K12 = 1.3 x 10–20 M2
H2S(aq) H2S(g)fromthioacetamidedecomposition 0.10 M
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Sulfide Ion Generation
[H2S] = 0.10 M
[H+] = 0.24 M
[S2–] = 2.3 x 10–20 M
H2S(aq) H2S(g)
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Which of the metal ions remain in solution and which precipitate?
Ni2+, Pb2+, Cu2+
2 drops 6 M HClthioacetamide
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Which of the metal ions remain in solution and which precipitate?
NiS:
Ksp, NiS = 3.0 x 10–21 M2
Ni2+ in solution
[Ni2+] [S2–] = (0.020)(2.3 x 10–20) = 4.6 x 10–22 M2
Determine if lead(II) ionwill precipitate or remain in solution.
This is what wehave
This is thesolubility limit compare these
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Which of the metal ions remain in solution and which precipitate?
PbS:
Ksp, PbS = 4.2 x 10–28 M2
PbS precipitates
[Pb2+] [S2–] = (0.020)(2.3 x 10–20) = 4.6 x 10–22 M2
< 4.6 x 10–22 M2
Determine if copper(II) ionwill precipitate or remain in solution.
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Which of the metal ions remain in solution and which precipitate?
CuS:
Ksp, CuS = 8.7 x 10–36 M2
CuS precipitates
[Cu2+] [S2–] = (0.004)(2.3 x 10–20) = 9 x 10–23 M2
< 9 x 10–23 M2
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Which of the metal ions remain in solution and which precipitate?
PbS, CuS
Ni2+, Pb2+, Cu2+
2 drops 6 M HClthioacetamide
Ni2+
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Metal Sulfide Dissolution Reactions
Sulfuric Acid
• The acidity of the solution will determine if the metal sulfide will dissolve.
FeS(s) + 2 H+(aq) Fe2+(aq) + H2S(g)
• 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.
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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.
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Metal Sulfide Dissolution Reactions
Hydrochloric Acid
CdS(s) + 2 H+(aq) + 4 Cl–(aq) [CdCl4]2– + H2S(g)
tetrachlorocadmate ion?
Cadmium sulfidewill not dissolve in 6 M sulfuric acidbut will dissolve in 6 M hydrochloric acid
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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.
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Metal Sulfide Dissolution ReactionsNitric Acid
Ag2S(s) + H+(aq) + NO3–(aq)
Ag+(aq) + NO2(g) + H2O(l) + S(s)
Ag2S(s) 2 Ag+(aq)
NO3–(aq) NO2(g)2 H+(aq) +e– + + H2O(l)
+ S(s) + 2 e–
2 242 2
4 2
2 2 2
Balance this redox equation in acidic solution
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End of Part 1
Be sure to review theExam I Objective Sheet
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
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