Question

Answer the questions below about a solution that is 0.0360 M in KClO4 and 0.0231 M in HClO4. What is the ionic strength? μ = What is the activity coefficient of H+ ion? γ = What is the activity of H+ ion? A = What is the pH of the solution? Take activity effects into account. pH =

Answer 1

a)

I.S...

Recall that ionic strength considers all ions in solution, and its charges. It is typically used to calculate the ionic activity of other ions. The stronger the electrolytes, the more ionic strength they will have.

The formula:

I.S. = 1/2*sum( Ci * Zi^2)

Where

I.S. = ionic strength, M (also miu / μ ) used

Ci = concentration of ion “i”

Zi = Charge of ion “i”

then

IS = 1/2*( (0.036)(1) + (0.036)(-1)^2 + (0.0231)(1)^2 +  (0.0231)(-1)^2)

IS = 0.0591 M

b)

Acitivty for H+

Recall that:

-log(γ) = 0.51*(Zi^2)*sqrt(I.S.) / ( 1 + (α * sqrt(I.S)/305))

Where

γi = activity coefficient for species “i”

αi = theoretical diameter in pm (10^-12 m)

Zi = Charge of ion

I.S. = ionic Strength (usually used as μ as well)

If we wanted only γ

γ = 10^-(0.51*(Zi^2)*sqrt(I.S.) / ( 1 + (α * sqrt(I.S)/305)))

for H+ , Zi = +1, IS = 0.0591 , α = 900

γ = 10^-(0.51*(1^2)*sqrt(0.0591) / ( 1 + (900 * sqrt(0.0591)/305)))

γ = 0.8468

c)

find acitvity of H+ ion

Activity = Y-H+ * [H*] = 0.8468 * 0.0231

Activity of H+ = 0.01956108

pH = -log(Activity of H+)

pH = -log(0.01956108) = 1.708