FORMATIVE ASSESSMENT: CHAPTER 19
Name:
1. Find the pH, pOH, [H+] and [OH-] of 5.5 x 10-4M Ba(OH)2
pH = 11.04
pOH = 2.96
[H+] = 9.1
x 10-12M
[OH-] = 0.0011M
SHOW ALL WORK FOR WEAK ACID AND WEAK BASE PROBLEMS, INCLUDING THE DISSOCIATION EQUATION,
CONCENTRATIONS AT EQUILIBRIUM, THE EQUATION FOR Ka (OR Kb) AND SUBSTITUTION.
2. Find the pH and % dissociation (ionization) of:
a.
0.0031M HCN
HCN ↔
init 0.0031M
Δ
-x
Eq 0.0031 –x
≈0.0031
(Ka = 4.0 x 10-10)
H+1
0M
+x
x
+
CN-1
0M
+x
x
Ka = [H+][CN-]
[HCN]
x2_____ = 4.0 x 10-10
0.0031
x = 1.11 x 10-6M = [H+]
pH = 5.95
b. 0.054M NaC2H3O2
H2O + C2H3O2- ↔
init 0.054M
Δ
-x
Eq 0.054 –x
≈0.054
pOH = 5.26
= 4.0 x 10-10
%d = 1.11 x 10-6/0.0031 x 100 = 0.036%
(Kb for C2H3O2- is 5.6 x 10-10)
HC2H3O2
0M
+x
x
+
pH = 8.74
OH-1
0M
+x
x
Kb = [OH-][ HC2H3O2]
[C2H3O2-]
= 5.6 x 10-10
x2_____ = 5.6 x 10-10
0.054
x = 5.50 x 10-6M = [OH-]
%d = 5.50 x 10-6/0.054 x 100 = 0.010%
3. The pH of a 0.450M solution of a weak acid, HX, is 2.475. Find the Ka of the acid.
HX ↔
init 0.450M
Δ
-0.00335M
Eq 0.44665M
H+1 +
0M
+0.00335M
0.00335M
X-1
0M
+0.00335M
0.00335M
Ka = [H+][X-]
[HX]
= ?
(0.00335M)2
0.44665M
=
2.51 x 10-5
4. A 0.0275M solution of a weak acid, HA is 6.54% dissociated. Find its Ka.
HA ↔
H+1 +
A-1
init 0.0275M
0M
0M
Δ
-0.001799M +0.001799M +0.001799M
Eq 0.0257M
0.001799M
0.001799M
Ka = [H+][A-]
[HA]
= ?
(0.001799M)2
0.0257M
=
1.26 x 10-4
5. 25.22mL of a 0.0453M solution of barium hydroxide is titrated with 15.76mL of phosphoric acid. Write the equation
for the reaction that occurs, and find the concentration of the phosphoric acid solution.
3 Ba(OH)2 + 2 H3PO4  Ba3(PO4)2 + 6 H2O
0.02522L x 0.04353mol Ba(OH)2 x 2 mol H3PO4 = 7.616 x 10-4 mol/0.01576L
1L
3 mol Ba(OH)2
= 0.0483M
6. The [IO3-] in a buffer solution is 0.045M. The [HIO3] in the same solution is 0.037M. Find the pH of the solution.
(Ka = 1.6 x 10-1)
HIO3 ↔
0.037M
0.16 = [H+] 0.045
0.037
H+1
0M
+
[H+] = 0.13M
IO3-1
0.045M
Ka = [H+][IO3-]
[HIO3]
pH = 0.88
= 0.16
Write the equation for the reaction that would occur if NaOH were added to the buffer solution.
OH- + HIO3  H2O + IO3Write the equation for the reaction that would occur if HCl were added to the buffer solution.
H+ + IO3-  HIO3
7. Label the salts below as acidic, basic or neutral.
KClO
Cu(NO3)2
LiF
NH4BrO
Basic
acidic
basic
neutral
8. Write the equation for the water dissociation of each Bronsted Lowry acid/base below. Label the weak acid, weak
base, conjugate acid and conjugate base.
HCHO + H2O ↔ H3O+ + CHOwa
wb
ca
cb
CH3NH2
wb
+ H2 O
wa
↔
OH- + CH3NH3+
cb
ca