In: Chemistry
Calculate the [H3O+] of the following polyprotic acid solution: 0.135 M H3C6H5O7.
Express your answer using two significant figures.
Calculate the pH of this solution
Express your answer to two decimal places.
For H3C6H5O7,
We have, ka1 = 7.5 x 10-4 > ka2 = 1.7 x 10-5 > ka3 = 4.0 x 10-7
Here, the second and third dissociations are negligible when compared to the first one
H3C6H5O7 + H2O H2C6H5O7- + H3O+
Initial 0.135 M 0 0
Change -x x x
Equilibrium 0.135-x x x
Ka1 = 7.5 x 10-4 = x2/(0.135-x) (x in the denominator can be neglected in comparison with 0.135 M)
Therefore,
x2 = 1.08 x 10-4
x = [H3O+] = 0.01 M
pH = -log[H3O+] = -log(0.01) = 2
pH = 2