ch17 keseimbangan ion

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:


Fenomena garam sukar larut dalam air

CaF2(s) Ca2+(aq) + 2F-(aq)

Contoh:


Konstanta hasil kali ion terlarut


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:


Arti konstanta hasil kali ion terlarut


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


(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]


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


I N/A 0 0C -x +x +x

E N/A x x

x2 = 1.8 10-10


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


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


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


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 >


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


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


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


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


Contoh:

20



Contoh:

21


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


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

= = =

=


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


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


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


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.


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


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-

ch17 keseimbangan ion

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