Recitation Section Problems
February 17, 2020
Solutions
1. The pKaof chlorous acid (HClO2) is 1.96. A buffer is made that is 1.20 M in chlorous
acid and 0.50 M in sodium chlorite (NaClO2). Calculate the pH of the resulting solution.
You must solve the full quadratic equation for this system.
Answer:
HClO2(aq)+ H2O(`)*
)H3O+
(aq)+ ClO−
2(aq)
Ka=[ClO−
2][H3O+]
[HClO2]= 10−1.96 = 1.1×10−2
[HClO2] [ClO−
2] [H3O+]
initial 1.20 M 0.50 M 0 M
change -y y y
equilibrium (1.20 -y) M (0.50 + y) M yM
y(y+ 0.50)
1.20 −y= 1.1×10−2
y2+ 0.51y−0.013 = 0
y=−0.51 ±[(0.51)2+ 4(0.013)]1/2
2= 2.5×10−2negative solution ignored
[H3O+] = 2.5×10−2M pH = −log10(2.5×10−2) = 1.61
1
