21
ACEE 219 ACEE 219 E i t lCh it E i t lCh it Environmental Chemistry Environmental Chemistry W k5 Week 5 March 30, 2010 Innovation Hall 127 ACEE 219 Spring 2010 HDP 1 Innovation Hall 127
ACEE 219ACEE 219E i t l Ch i tE i t l Ch i tEnvironmental ChemistryEnvironmental Chemistry
W k 5Week 5March 30, 2010
Innovation Hall 127
ACEE 219 Spring 2010 HDP 1
Innovation Hall 127
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH Diagram
pC-pH diagram for 10-3 moles of HCN to 1 liter of pure water.
1. Mass balance on CNCT,CN = [HCN] + [CN-] = 10-3
2. Equilibrium relationshipsKw = [H+][OH-] = 10-14
3.9-
a 10[HCN]]][CN[HK
+==
3. Charge balance, Proton condition[H+] = [CN-] + [OH-]
ACEE 219 Spring 2010 HDP 2
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
2
4
n
,
p
C Line 1 (pCT - pH)- logCT CN = pCT CN = 3
6
e
n
t
r
a
t
i
o
n
logCT,CN pCT,CN 3
8
10
l
o
g
C
o
n
c
12
14
l
ACEE 219 Spring 2010 HDP 3
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
2
4
n
,
p
C
Line 2 (pOH - pH)
-logKw = -log[H+] - log[OH-]
6
e
n
t
r
a
t
i
o
n
14 = pH + pOH
pOH = 14 - pH8
10
l
o
g
C
o
n
c
12
14
l
ACEE 219 Spring 2010 HDP 4
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
2
4
n
,
p
C
6
e
n
t
r
a
t
i
o
n
8
10
l
o
g
C
o
n
c Line 3 (pH - pH)
- log[H+] = pH
12
14
l
ACEE 219 Spring 2010 HDP 5
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
2
4
n
,
p
C
Line 4 (pCN - pH)6
e
n
t
r
a
t
i
o
n Line 4 (pCN - pH)when Ka >> [H+] (i.e., pH > pKa)
1 = C][CN CNT,8
10
l
o
g
C
o
n
c
10
3
1
+= +C][CN
CK][HK
][CNT,
aa
CNT,
12
14
l
3
10 3
===
]p[CNC][CN CNT,
ACEE 219 Spring 2010 HDP 6
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
2
4
n
,
p
C
1 = C][CN CNT,6
e
n
t
r
a
t
i
o
n
+= +K
CK][HK
CNT,a
a
,
8
10
l
o
g
C
o
n
c
pCpHp CNT,a +==
+
K]p[CNC][H
K][CN CNT,a
12
14
l
Li 5 ( CN H)
pH - 12.3 ,
=
ACEE 219 Spring 2010 HDP 7
Line 5 (pCN - pH)when Ka
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
Line 6 (pHCN - pH)2
4
n
,
p
C
Line 6 (pHCN - pH)when Ka
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH
0
0 2 4 6 8 10 12 14
pH
Line 7 (pHCN)2
4
n
,
p
C
Line 7 (pHCN)when Ka >> [H+] (i.e., pH > pKa)
0 = C[HCN] CNT,6
e
n
t
r
a
t
i
o
n
+=+
++
CK][H][H
CNT,a
,
8
10
l
o
g
C
o
n
c
pCp-pH CNTa +==
+
K]p[CNCK
][H[HCN] CNT,a
12
14
l
6.3- pH pCpp CNT,a
=]p[
ACEE 219 Spring 2010 HDP 9
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH Diagram
2
6 7 8 9 10 11 12
pH
pKa
2.5
3
o
n
,
p
C
0.3 unit below CT
1.0 unit right pKa1.0 unit left pKa
3 33.5
4
c
e
n
t
r
a
t
i
o
T
logC = log([CN]+[HCN])
3.3
4.5
5
l
o
g
C
o
n
c
logCT = log([CN]+[HCN])= log2[HCN]
log[HCN] = logCT - log25.5
6
log[HCN] logCT log2= - 3 -log2 = -3.3
8.3 9.3 10.3
ACEE 219 Spring 2010 HDP 10
pCpC pH DiagrampH DiagrampCpC--pH DiagrampH DiagrampH pK = 9 3
0
0 2 4 6 8 10 12 14
pH pKa = 9.3
2
4
n
,
p
C pCT,CN = 3
6
e
n
t
r
a
t
i
o
n
[HCN]
[CN-]8
10
l
o
g
C
o
n
c
[H+][OH ]
[CN ]
12
14
l [H+][OH-]
ACEE 219 Spring 2010 HDP 11
How to determine Eq. pHHow to determine Eq. pHusing using pCpC--pH diagrampH diagram
Find pH (or pOH) where the proton condition or charge balanceis satisfied.
0
0 2 4 6 8 10 12 14
C
pH[H+] [OH-]
Example 4-162
4
a
t
i
o
n
,
p
C
[HCN] [CN-]
Example 4-1610-3 M HCNProton condition:
6
8
10on
c
e
n
t
r
a
[H+] = [CN-] + [OH-]
10
12
14
l
o
g
C
ACEE 219 Spring 2010 HDP 12
6.2 (equilibrium pH)
How to determine Eq. pHHow to determine Eq. pHusing using pCpC--pH diagrampH diagram
Find pH (or pOH) where the proton condition or charge balanceis satisfied.
0
0 2 4 6 8 10 12 14
C
pH[H+] [OH-]
Example 4-172
4
a
t
i
o
n
,
p
C
[HCN] [CN-]
Example 4-1710-3 M NaCNProton condition:
6
8
10on
c
e
n
t
r
a
[HCN] + [H+] = [OH-]
10
12
14
l
o
g
C
ACEE 219 Spring 2010 HDP 13
10.1 (equilibrium pH)
HOClHOClHOClHOCl
Draw a pC-pH diagram for 1.5x10-4 moles of HOCl to 1 liter of pure water.
1. Mass balance on OClCT,OCl = [HOCl] + [OCl-] = 1.5x10-4 (pCT,OCl = 3.8)
2. Equilibrium relationshipsKw = [H+][OH-] = 10-14
5.7+
== 10[HOCl]
]][OCl[HK-
a
3. Charge balance, Proton condition[H+] = [OCl-] + [OH-]
ACEE 219 Spring 2010 HDP 14
HOClHOClHOClHOClpH
0
0 2 4 6 8 10 12 14
pHpKa = 7.5
2
4
o
n
,
p
C
pCT,CN = 3.8
6
8
c
e
n
t
r
a
t
i
o
[HOCl][OCl-]8
10
l
o
g
C
o
n
c
[H+]
[OH-]12
14
[OH ]
ACEE 219 Spring 2010 HDP 15
HOClHOClHOClHOCl
0 2 4 6 8 10 12 14
pH
0
2
,
p
C
[H+] [OH-]
1 5 x 10-4 M HOCl4
6
n
t
r
a
t
i
o
n
,
[HOCl]
1.5 x 10 M HOClProton condition:[H+] = [OCl-] + [OH-]
8
10
g
C
o
n
c
e
n [HOCl][OCl-]
How about 1.5 x 10-4 M NaOCl ?
12
14
l
o
5 7 (equilibrium pH)
ACEE 219 Spring 2010 HDP 16
5.7 (equilibrium pH)
MultiproticMultiprotic AcidAcidMultiproticMultiprotic AcidAcid Example Draw a pC-pH diagram for 10-2 moles of H2A to 1 liter of pure water.
1 M b l OCl1. Mass balance on OClCT,A = [H2A] + [HA-] + [A2-] = 10-2 (pCT,A = 2)
2 E ilib i l ti hi2. Equilibrium relationshipsKw = [H+][OH-] = 10-14
4+
10]][HA[HK-
4== 10A][H
]][[K2
a,1
8+
== 10]][A[HK-2
a 2
3. Charge Balance[H+] = [OH-] + [HA-] + [A2-]
0][HA-a,2
ACEE 219 Spring 2010 HDP 17
[H ] [OH ] [HA ] [A ]
MultiproticMultiprotic AcidAcidMultiproticMultiprotic AcidAcidpH
0
0 2 4 6 8 10 12 14
pHpKa1= 4.0 pKa2= 8.0
[A2 ]2
4
n
,
p
C
[H2A]pCT,A = 2
[A2-]
6
e
n
t
r
a
t
i
o
n
[HA-]
8
10
o
g
C
o
n
c
e
12
14
l
o
[H+][OH-]
ACEE 219 Spring 2010 HDP 18
14
MultiproticMultiprotic AcidAcidMultiproticMultiprotic AcidAcid
0
0 2 4 6 8 10 12 14
pH
[H+] [OH-]0
2
4n,
p
C
[H+] [OH-]
[H2A] [HA-] [A2-]Example 4-20 (1)4
6
8en
t
r
a
t
i
o
n Example 4-20 (1)10-2 M H2AProton condition:
8
10
o
g
C
o
n
c
e
[H+] = [HA-] + 2[A2-] + [OH-]
12
14
l
3.05 (equilibrium pH)
ACEE 219 Spring 2010 HDP 19
MultiproticMultiprotic AcidAcidMultiproticMultiprotic AcidAcid
0
0 2 4 6 8 10 12 14
pH
[H+] [OH-]0
2
4n,
p
C
[H+] [OH-]
[H2A] [HA-] [A2-]Example 4-20 (1)4
6
8en
t
r
a
t
i
o
n Example 4-20 (1)10-2 M Na2AProton condition:
8
10
o
g
C
o
n
c
e
2[H2A] + [HA-] + [H+] = [OH-]
12
14
l
10 (equilibrium pH)
ACEE 219 Spring 2010 HDP 20
Summary for the Exam1Summary for the Exam1Summary for the Exam1Summary for the Exam1
1. Features of Water2 Rate laws (0 1st 2nd order chemical kinetics)2. Rate laws (0, 1st, 2nd order chemical kinetics)3. Arrhenius equation4 Bi l i l ki ti4. Biological kinetics5. Chemical equilibrium6. Gibbs free energy7. Equilibrium constant & effect of temperature on K8. Numerical and graphical methods for estimating
acid and base equilibrium concentrations.
ACEE 219 Spring 2010 HDP 21
acid and base equilibrium concentrations.