Question

Calculate the acid dissociation constant of a weak monoprotic acid if a 0.5M solution of this acid gives a hydrogen-ion concentration of 0.000 1M? Show your work.

Answer 1

First we create a balanced equation

HA <-> H(+) + A(-)

Then, we set up an ICE table

        HA <--> H(+) +        A(-)
[]i     0.5M      0M             0M
Δ[]   -x           +x              +x
[]f     0.5M-x   0.0001M    0.0001M

From this, we can say that x = 0.0001.

Next, we set up the equation

Ka = [H+][A-]/[HA]

Ka = [0.0001][0.0001]/[0.5-0.0001]

Ka = 2x10^-8