1Chapter 17 Kelarutan dan Keseimbangan
Brady and Senese5th Edition
Fakta-fakta menunjukkan terdapat sejumlah garam yang mudah larut (... NaCl dan AgNO3, ...) dan yang tidak larut (... AgCl dan CaCO3, ...).
Kenyataannya: pada garam-garam tidak larut, ketika dimasukkan ke dalam air, terdapat sejumlah kecil garam yang larut dan membentuk suatu keseimbangan ion-ion terlarut, contoh:
Kajian lebih lanjut menunjukkan setiap garam tidak larut memiliki karakteristik kelarutan masing-masing, yang ditunjukkan oleh nilai keseimbangan Ksp.
17.1. An insoluble salt is in equilibrium with the solution around it 2
Fenomena garam sukar larut dalam air
AgCl(s) Ag+(aq) + Cl-(aq)
Fakta-fakta menunjukkan terdapat sejumlah garam yang mudah larut (... NaCl dan AgNO3, ...) dan yang tidak larut (... AgCl dan CaF2, ...).
Kenyataannya: pada garam-garam tidak larut, ketika dimasukkan ke dalam air, terdapat sejumlah kecil garam yang larut dan membentuk suatu keseimbangan ion-ion terlarut, contoh:
17.1. An insoluble salt is in equilibrium with the solution around it 3
Fenomena garam sukar larut dalam air
CaF2(s) Ca2+(aq) + 2F-(aq)
Contoh:
17.1. An insoluble salt is in equilibrium with the solution around it 4
Konstanta hasil kali ion terlarut
AgCl(s) Ag+(aq) + Cl-(aq)
Ksp = [Ag+][Cl] = 1,8 10-10konstanta hasil kali ion terlarut
Kajian lebih lanjut menunjukkan setiap garam tidak larut
memiliki karakteristik kelarutan masing-
masing, yang ditunjukkan oleh nilai
keseimbangan Ksp.
Contoh:
17.1. An insoluble salt is in equilibrium with the solution around it 5
Arti konstanta hasil kali ion terlarut
AgCl(s) Ag+(aq) + Cl-(aq)
Ksp = [Ag+][Cl] = 1,8 10-10
Kelarutan AgCl = 1,34 x 10-5 M
Nilai yang tetap pada suhu tetap penambahan salah satu ion ke
dalam air akan mengurangi kelarutan (efek ion senama)
Apabila dalam suatu larutan hasil kali ion-ion terlarut (Q) melebihi Ksp garam akan diendapkan digunakan sebagai dasar pada pemurnian dengan cara kristalisasi
Q > Ksp lewat jenuhQ = Ksp jenuhQ < Ksp tidak jenuh
Contoh:
6
Efek ion senama
17.1. An insoluble salt is in equilibrium with the solution around it 7
(NH4)2SO4(s) 2NH4+(aq) + SO42-(aq)
Ag2CO3(s) 2Ag+(aq) + CO32-(aq)
Learning Check
Write the reactions and mass action expressions for the dissolution of the following substances in water:
Ag2CO3
(NH4)2SO4Ksp = [Ag+]2[CO32]
Ksp = [NH4+]2[SO42]
17.1. An insoluble salt is in equilibrium with the solution around it 8
Learning Check
What is the molar solubility of AgCl at 25 C?
AgCl Ksp 1.8 10-10
molar solubility = 1.3 10-5 M
AgCl(s) Ag+(aq) + Cl-(aq)
I N/A 0 0C -x +x +x
E N/A x x
x2 = 1.8 10-10
17.1. An insoluble salt is in equilibrium with the solution around it 9
Learning Check
What is the molar solubility of Ca3(PO4)2 at 25 C?
Ca3(PO4)2 Ksp 2.0 10-29
> molar solubility = 7.1 10-7 M
I N/A 0 0C -x +3x +2xE N/A 3x 2x
Ca3(PO4)2(s) 3Ca2+(aq) + 2PO43-(aq)
> (3x)3(2x)2 = Ksp
17.1. An insoluble salt is in equilibrium with the solution around it 10
Your Turn!
What is the molar solubility of Ba3(PO4)2?Ksp = 1.30 10-29
A. 1.17 10-7 MB. 2.17 10-20 MC. 6.55 10-7 MD. None of these
17.1. An insoluble salt is in equilibrium with the solution around it 11
Learning Check
Given solubilities, we can find Ksp The solubility of an salt, A2B3, is found to be
3.0 10-5 M. What is the value of Ksp?
If the solubility of a salt, AB2, is found to be 2.5 10-6 M, what is its Ksp?
6.3 10-17
2.6 10-21
17.1. An insoluble salt is in equilibrium with the solution around it 12
Learning Check: Common Ion Effect
What is the molar solubility of Ca3(PO4)2 in 0.1 MNa3PO4? Ksp= 2.0 1029
molar solubility 4.2 10-10 M
1. Na3PO4 is strong electrolyte - ionized at the startNa3PO4 3Na+(aq) + PO43-(aq)0.1 M 0.3 M 0.1 M
I N/A 0 0.1 MC -x +3x +2xE N/A 3x 0.1 + 2x 0.1
2. Ca3(PO4)2 3Ca2+(aq) + 2PO43-(aq)
> (3x)3(0.1)2 = Ksp >
17.1. An insoluble salt is in equilibrium with the solution around it 13
Learning Check: Common Ion Effect
Calculate the molar solubility of BaSO4 in 0.1 MBaCl2. Ksp = 1.1 10-10
> 1.1 10-9 M
1. BaCl2 is a strong electrolyte.
BaCl2 Ba2+(aq) + 2Cl-(aq)0.1 M 0.1 M 0.2 M
2. BaSO4(s) Ba2+(aq) + SO42-(aq) I N/A 0.1 M 0C -x +x +xE N/A 0.1 + x 0.1 x
> x(0.1) = Ksp
17.1. An insoluble salt is in equilibrium with the solution around it 14
Your Turn!
What will happen to the solubility of Ba3(PO4)2 if solid BaCl2 is added?
A. It increasesB. It decreasesC. It does not changeD. Not enough information given
17.1. An insoluble salt is in equilibrium with the solution around it 15
Learning Check
Will the following form a precipitate? 20.00 mL of 0.1 M CaCl2 + 20.00 mL 0.01 M Na2CO4
10.00 mL of 0.1 M Pb(NO3)2 + 10.00 mL of 0.001 M CaCl2
Qsp = 1.3 10-8
Qsp = 0.00025
CaC2O4(s) Ca2+(aq) + C2O42-(aq) Ksp = 2.3 109
Ksp = 2.3 109 = [Ca2+][C2O42]
PbCl2(s) Pb2+(aq) + 2Cl-(aq) Ksp = 1.7 105
Ksp = 1.7 105 = [Pb2+][Cl-]2
Qsp > Ksp a precipitate will form
Qsp < Ksp no precipitate will form
17.1. An insoluble salt is in equilibrium with the solution around it 16
Your Turn!
Pb(NO3)2 is added to a solution of HCl until the mixture is 0.1 M in Pb2+ and 0.005 M in Cl-. Will a precipitate form? Ksp = 1.7 10-5
A. NoB. YesC. Not enough information is given
Garam-garam atau oksida yang sukar larut dalam air, dapat ditingkatkan kelarutannya dengan penambahan asam
Contoh:
17
Meningkatkan kelarutan garam atau oksida
Ksp (CaCO3) 1/K2 (H2CO3)
Ktotal = Ksp (CaCO3)/K2 (H2CO3)
Ksp (CaCO3) = 4,5 x 10-9
K2 (H2CO3) = 4,7 x 10-11
Ktotal = 4,5 x 4,7 x 102 = 2,1 x 103
Ktotal =[Ca2+] [HCO3-]
[H3O+]
[Ca2+] [HCO3-] = [H3O+] 2,1 x 103
jauh lebih besar dari Ksp
kelarutan semakin besar jika [H3O+] semakin tinggi
18
Meningkatkan kelarutan garam atau oksida
Kelarutan CaCO3semakin bertambah pada kondisi larutan yang lebih asam
Garam-garam yang sukar larut dalam air, dapat ditingkatkan kelarutannya dengan penambahan basa Lewis senyawa kompleks
Contoh:
19
Meningkatkan kelarutan garam
AgCl dalam
air
AgCl dalam air dan ditambah-kan NH3
Garam-garam yang sukar larut dalam air, dapat ditingkatkan kelarutannya dengan penambahan basa Lewis senyawa kompleks
Contoh:
20
Meningkatkan kelarutan garam
Garam-garam yang sukar larut dalam air, dapat ditingkatkan kelarutannya dengan penambahan basa Lewis senyawa kompleks
Contoh:
21
Meningkatkan kelarutan garam
17.2. Solubility equilibria of metal oxides and sulfides involve reaction with water 22
b(aq)(l)2 (aq)-2 K OH 2 O HO +
net (aq)-
(aq)(l)2(s)2 K2OH Ag 2 OH OAg ++ +
sp (aq)-2
(aq)(s)2 KO Ag 2 OAg + +
Kelarutan oksida dan sulfidaKelarutan oksida atau sulfida dalam air bisa terjadi karena O2- atau S2-bersifat sangat basa, sehingga bereaksi dengan air membentuk OH-
Contoh:
S2-(aq) + H2O OH-(aq) + HS-(aq) KbAg2S(s) + H2O OH-(aq) + HS-(aq) + 2Ag+(aq) Knet
Ag2S(s) 2Ag+(aq) + S2-(aq) Ksp
17.2. Solubility equilibria of metal oxides and sulfides involve reaction with water 23
Learning CheckWhat is the molar solubility of BaCO3 in 3 M HCl?
BaCO3 Ksp = 5.0 109
H2CO3 Ka1= 4.3 107 Ka2 = 4.7 10
11
1.50 M
BaCO3(s) + 2H+(aq) H2CO3(aq) + Ba2+(aq)I N/A 3 0 0C -x -2x +x +xE N/A 3 - 2x x x
( ) ( )( )
1 2
9sp 10
net 9 11a a
210
2
K 5.0 10K 2.47 10K K 4.3 10 4.7 10
x 2.47 103 2x
= = =
=
17.2. Solubility equilibria of metal oxides and sulfides involve reaction with water 24
Your Turn!
What is Knet for the molar solubility of Ba3(PO4)2 in 6 M HCl?
Ba3(PO4)2(s) + 6HCl(aq) 2H3PO4(aq) + 3BaCl2(aq)
1 2 2
1 2 2
sp2
a2
a
sp
2 2 2a a a
sp
sp2 2 2
a a a
KA.
K
KB.
K
K K KC.
K
KD.
K K K
17.3. Metal ions can be separated by selective precipitation 25
Pengendapan garam secara selektifSuatu ion dapat berkompetisi dalam mengendapkan suatu garam dari campuran ion-ion karena nilai Ksp yang berbeda-beda
Contoh: penambahan ion Cl- ke dalam campuran garam nitrat dari Ag dan Pb, akan mengendapkan AgCl ketika nilai Ksp-nya terlampaui
Learning CheckWhat concentration of I- is needed to precipitate one ion but not the other in a mixture of 0.1 M Pb2+ and 0.1 M Ag+?
[I-] = 8.3 10-16 M
AgI(s) Ag+(aq) + I-(aq)Ksp = [Ag+][I-] = 8.3 10-17
PbI2(s) Pb2+(aq) + 2I-(aq)Ksp = [Pb2+][I-]2 = 7.9 10-9
batas konsentrasi I- jenuh
AgI mengendapAgI tdk mengendap
[I-] = 2.8 10-4 M
batas konsentrasi I- jenuh
PbI2 mengendapPbI2 tdk mengendap
AgI
PbI2
AgI dan PbI2 tidak mengendap
AgI mengendapPbI2 tdk mengendap
AgI dan PbI2mengendap
17.3. Metal ions can be separated by selective precipitation 27
Learning CheckAt what pH will one ion ppt but not the other in a mixture of 0.1 M Mn2+, 0.1 M Fe3+?
Fe: pH = 1.40 Mn: pH = 8.10
pH
Fe(OH)3(s) Fe3+(aq) + 3OH-(aq)Ksp = [Fe3+][OH-]3 = 1.6 10-39
Mn(OH)2(s) Mn2+(aq) + 2OH-(aq)Ksp = [Mn2+][OH-]2 = 1.6 10-13
17.3. Metal ions can be separated by selective precipitation 28
Your Turn!
When a solution containing 0.1 M Ca2+ and 0.01 MMg2+, what concentration of CO32- will precipitate one but not the other?
A. 5 10-8
B. 5 10-7
C. 5 10-6
D. All of these will doE. None of these will do
KspCaCO3 4.8 10-9
MgCO33H2O 4.0 10-5
17.3. Metal ions can be separated by selective precipitation 29
Learning CheckWhat pH will prevent the precipitation of any metal ions in 0.1 M H2S, 0.1 M Cu2+, and 0.1 M Pb2+?
[ ]2+ 2162+
Cu H S6 10
H
=
[ ]2+ 272+
Pb H S3 10
H
=
pH
CuS pH= -6.61 PbS pH= -2.26
Cu2+(aq) + H2S(aq) 2H+(aq) + CuS(s)Kspa = 6 1016
Pb2+(aq) + H2S(aq) 2H+(aq) + PbS(s)Kspa = 3 107
17.4 Complex ions participate in equilibria in aqueous solutions 30
Complexation and Kinst
Complex ions are charged particles in which a metal ion is surrounded by anions or molecules called ligands, L
Complex ions are soluble, hence complexation is a means of dissolving some solids
Complexes are governed by the instability constant, Kinst
M(L)nm+(aq) Mm+(aq) + nL(aq) When we reverse an equation, we invert K, thus
Kform = 1/Kinst.
17.4 Complex ions participate in equilibria in aqueous solutions 31
Aqueous Metal Ions are Complex Ions
In the solvation of ionic compounds, ions are dissolved in water through ion-dipole interactions
Water acts as a ligand, the Lewis base that forms a coordinate covalent bond with the metal
17.4 Complex ions participate in equilibria in aqueous solutions 32
Learning Check
What is the concentration of Cu2+ available when 10.0 mL 0.1 M Cu2+ are combined with 10.0 mL of 0.01 M NH3?
Kform = 1.1 1013
0.048 M
Cu2+(aq) + 4NH3(aq) [Cu(NH3)4]2+(aq)
17.5 Complex ion formation increases the solubility of a salt 33
Learning Check
Calculate the molar solubility of Ag2S in 2 M NH3.Ag2S Ksp = 6.0 10-51 [Ag(NH3)2+] Kinst= 6.3 108
Ag2S(s) + 4NH3(aq) 2[Ag(NH3)2]+ + S2-(aq)
1.8 10-12 M
17.5 Complex ion formation increases the solubility of a salt 34
Your Turn!
What is the molar solubility of Co2S3 in 6.0 M NH3 A. 1.8 10-11 MB. 4.6 10-57 MC. 2.3 10-3 MD. None of these
[Co(NH3)6]3+ Kinst = 2.2 10-34
Co2S3 Ksp = 2.6 10 -124
2 3sp 57
212inst
557
12
(2x) (3x) 5.37 10(6 12x)
108x 5.37 106
= = =
KK
x = 1.61 10-10
Co2S3 + 12NH3 2Co(NH3)63+ + 3S2-
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