Salt Ion(s) that will hydrolyze Spectator Ions Universal indicator color Measure

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

A)

Using the published Ka values for HC2H3O2 and HCO3-, calculate the Kb’s for the C2H3O2- and CO32- ions. Compare these values with those calculated from your measured pH’s. Constants are found in appendix D of your textbook.

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

from standard data

Ka of CH3COOH = 1.8*10^-5

so that

kb of CH3COO- = 10^-14/(1.8*10^-5 ) = 5.5*10^-10

Ka of HCO3- = 5.6*10^-11

so that

kb of CO3^2- = 10^-14/(5.6*10^-11) = 1.78*10^-4

BUT calculated value

kb of CH3COO- = 2.51*10^-12

kb of CO3^2- = 2.54*10^-5

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