Salt Ion(s) that will hydrolyze Spectator Ions Universal indicator color Measure
ID: 1004688 • Letter: S
Question
Salt
Ion(s) that will hydrolyze
Spectator Ions
Universal indicator color
Measured pH (sensor)
[H+] From pH
[OH-] From pH
Net Ionic equation
Ka/Kb expression
Ka/Kb value (use ICE tables)
Tap
Water
------
------
Gn
8.46
3.46E-9
2.88E-6
------
------
------
D.I.
H2O
------
------
Or
5.00
1.00
E-5
1.00E-9
------
------
------
NaCl
------
Na+,Cl-
Y/Or
6.40
3.89E-7
2.51E-8
------
------
------
NaC2H3O2
C2H3O2-
Na+
Y/Gn
7.70
2.00
E-8
5.01E-7
C2H3O2-+H2O <->HC2H3O2+OH-
Kb= 2.51E-12
NH4Cl
NH4+
Cl-
Y
5.84
1.45E-6
6.92E-9
NH4++H2O <-> NH4OH + H+
Ka = 2.10E-11
ZnCl2
Zn2+
2Cl-
Y
4.49
3.24E-5
3.09E-10
Zn2++H2O <-> ZnOH+ + H+
Ka = 1.05E-8
KAl(SO4)2
Al3+
K-2SO4-
R
3.03
9.33E-4
1.01E-11
Al3++H2O <-> AlOH2++H+
Ka = 8.79E-6
Na2CO3
CO32-
2Na+
Dark Blue
11.2
6.31E-12
1.58E-3
CO32-+H2O <-> HCO3-+OH-
Kb = 2.54E-5
B)
Using Kb for NH3, calculate Ka for the NH4+ ion. Compare this value with that calculated from your measured pH’s.
Salt
Ion(s) that will hydrolyze
Spectator Ions
Universal indicator color
Measured pH (sensor)
[H+] From pH
[OH-] From pH
Net Ionic equation
Ka/Kb expression
Ka/Kb value (use ICE tables)
Tap
Water
------
------
Gn
8.46
3.46E-9
2.88E-6
------
------
------
D.I.
H2O
------
------
Or
5.00
1.00
E-5
1.00E-9
------
------
------
NaCl
------
Na+,Cl-
Y/Or
6.40
3.89E-7
2.51E-8
------
------
------
NaC2H3O2
C2H3O2-
Na+
Y/Gn
7.70
2.00
E-8
5.01E-7
C2H3O2-+H2O <->HC2H3O2+OH-
Kb= 2.51E-12
NH4Cl
NH4+
Cl-
Y
5.84
1.45E-6
6.92E-9
NH4++H2O <-> NH4OH + H+
Ka = 2.10E-11
ZnCl2
Zn2+
2Cl-
Y
4.49
3.24E-5
3.09E-10
Zn2++H2O <-> ZnOH+ + H+
Ka = 1.05E-8
KAl(SO4)2
Al3+
K-2SO4-
R
3.03
9.33E-4
1.01E-11
Al3++H2O <-> AlOH2++H+
Ka = 8.79E-6
Na2CO3
CO32-
2Na+
Dark Blue
11.2
6.31E-12
1.58E-3
CO32-+H2O <-> HCO3-+OH-
Kb = 2.54E-5
Explanation / Answer
Kb of NH3 = 1.8*10-5
Kw = 10-14
Ka = Kw/Kb = 10-14/1.8*10-5
= 0.56*10-9 = 5.6*10-10
For reaction from table,
NH4++H2O <-> NH4OH + H+
At pH = 5.84, obtained Ka = 2.10*10-11
% error = Obtained/theoretical*100
= (2.10*10-11/5.6*10-10)*100
= 3.75%
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