PH and the Acid Dissociation Constant

[Soaring Crane]

1. What is the hydronium ion concentration and the pH for an aqueous solution of NH3 that has a hydroxide ion concentration of 2.25E-3 M?

a. 4.44 x 10-11 M, 3.65
b. 4.44 x 10-11 M, 10.35
c. 4.44 x 10-12 M, 2.65
d. 4.44 x 10-12 M, 11.35

[OH] = 2.25E-3
pOH = -log(2.25E-3) = 2.6478
-log[H3O+] = 14 - 2.6478 = 11.352 = pH
[H3O+] = antilog(-11.352] = 4.44E-12


2. Determine the acid dissociation constant for a 0.010 M nitrous acid solution that has a pH of 2.70. Nitrous acid is a weak monoprotic acid and the equilibrium equation of interest is HNO2 + H2O <-> H3O+ + NO2-.

a. 8.0 x 10-3
b. 2.0 x 10-3
c. 5.0 x 10-4
d. 4.0 x 10-4

K_a = [NO2-][H30+]/[HNO2]

pH = -log[H3O+]
2.70 = -log[H3O+]
[H3O+] = antilog(-2.70) = 0.001995 M

K_a = [0.001995 M]^2/[0.010 M - 0.001995 M] = 4.97E-4

Thanks.

 

[Borek]

2xOK