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P G6 Salt Hydrolysis Name______________________________Per___
- Which of the following salts, when dissolved in water, at 25ºC, cause a change in pH? If there is a pH change, will the pH be
above or below 7? Write a hydrolysis reaction that illustrates the cause of the pH change. Calculate the pH if 2.0 g of the salt
is dissolved to make 100 ml of solution.
a. barium chloride, BaCl 2 (208.2 g/mol) Acidic, Basic or Neutral?
b. ammonium perchlorate, NH 4 ClO 4 (117.492 g/mol) Acidic, Basic or Neutral?
c. sodium cyanide, NaCN (49.01 g/mol) Acidic, Basic or Neutral?
d. ammonium nitrate, NH 4 NO 3 (80.052 g/mol) Acidic, Basic or Neutral?
e. potassium acetate, KC 2 H 3 O 2 (98.144 g/mol) Acidic, Basic or Neutral?
f. diethylamide bromide, (C 2 H 5 ) 2 NH 2 Br (154.046 g/mol) Acidic, Basic or Neutral?
g. aluminum perchlorate, Al(ClO 4 ) 3 (325.33 g/mol) Acidic, Basic or Neutral?
K
w
= H
OH
−
K
a
× K
b
= K
w
M × V = M × V
B + H 2 O OH
+ HB
K
b
OH
−
HB
⎡ B
Li OH
Na OH
K OH
Rb OH
Cs OH
Ca (OH) 2
Sr (OH) 2
Ba (OH) 2
Strong Bases
HA H
+ A
K
a
H
A
−
⎡ HA
H Cl
H Br
H I
H NO 3
H 2 SO 4
H ClO 4
H ClO 3
Strong Acids
Really useful
information
Equilibrium Konstants
Ka or Kb as appropriate for
the listed substance.
HCN Ka = 4.9 × 10 − 10
HF Ka = 3.5 × 10 − 4
HC 2 H 3 O 2 Ka = 1.8 × 10 − 5
Al 3+ Ka = 1.5 × 10 − 5
NH 3 Kb = 1.8 × 10 − 5
(C 2 H 5 ) 2 NH Kb = 1.3 × 10 − 3
P G6 Salt Hydrolysis ANSWERS
- Which of the following salts, when dissolved in water, at 25ºC, cause a change in pH? If there is a pH change, will the pH be
above or below 7? Write a hydrolysis reaction that illustrates the cause of the pH change. Calculate the pH if 2.0 g of the salt
is dissolved in 100 ml of water.
a. barium chloride, BaCl 2 (208.2 g/mol)
b. ammonium perchlorate, NH 4 ClO 4 (117.492 g/mol)
c. sodium cyanide, NaCN (49.01 g/mol)
d. ammonium nitrate, NH 4 NO 3 (80.052 g/mol)
2 g ×
1 mol
49.01 g
= 0.0408 mol
0.0408 mol
0.1 L
= 0.408 M K
a
× K
b
= K
w
1 × 10
− 14
3.5 × 10
− 4
= 2.9 × 10
− 11
K
b
OH
−
[ HCN ]
CN
−
2.9 × 10
− 11
x
2
[ 0.408]
x = OH
−
= 3.4 × 10
− 6
pOH = 5.47 pH = 8.
2 g ×
1 mol
80.052 g
= 0.025 mol
0.025 mol
0.1 L
= 0.250 M K
a
× K
b
= K
w
1 × 10
− 14
1.8 × 10
− 5
= 5.56 × 10
− 10
K
b
H
NH
[ 3 ]
NH
4
5.56 × 10
− 10
x
2
[^ 0.25 ]
x = H
= 1.2 × 10
− 5
pH = 4.
pH will remain at 7. BaCl 2 → Ba 2+
- 2 Cl − (note the single arrow since BaCl 2 is a soluble ionic compound). The
Ba 2+ ions are “pathetic” meaning they do not hydrolyze in water and thus do not produce any extra H
or OH − ions. The
Cl − ions are also “pathetic” meaning they do not hydrolyze in water and thus do not produce any extra H
or OH − ions.
pH will change to above 7, basic. NaCN → Na
- CN − (note the single arrow since NaCN is a soluble ionic compound)
The Na
ions are “pathetic” meaning they do not hydrolyze in water and thus do not produce any extra H
or OH − ions. But the
CN
− ions are a conjugate WB which hydrolyzes in water and produces extra OH − ions. CN −
pH will change to below 7, acidic. NH 4 NO 3 → NH 4
- NO 3 − (note the single arrow since NH 4 NO 3 is a soluble ionic
compound) The NO 3 − ions are are “pathetic” meaning they do not hydrolyze in water and thus do not produce any extra H
or
OH
− ions. But the NH 4
ions are a conjugate WA and partially dissociate in water and produce H
ions. NH 4
H
pH will change to below 7, acidic. NH 4 ClO 3 → NH 4
- ClO 3 − (note the single arrow since NH 4 ClO 3 is a soluble ionic
compound) The ClO 3 − ions are are “pathetic” meaning they do not hydrolyze in water and thus do not produce any extra H
or
OH
− ions. But the NH 4
ions are a conjugate WA and partially dissociate in water and produce H
ions. NH 4
H
2 g ×
1 mol
80.052 g
= 0.025 mol
0.025 mol
0.1 L
= 0.250 M K
a
× K
b
= K
w
1 × 10
− 14
1.8 × 10
− 5
= 5.56 × 10
− 10
K
b
H
NH
[ 3 ]
NH
4
5.56 × 10
− 10
x
2
[^ 0.25 ]
x = H
= 1.2 × 10
− 5
pH = 4.
117.492 g
0.017 mol
0.017 mol
0.17 M
[0.17 M]
9.7 × 10
− 6
