Question

Calculate the [H3O+] of the following polyprotic acid solution: 0.145M H3C6H5O7.

Calculate the pH of this solution.

Answer 1

ka1=7.5x10^-4

ka2=1.7x10^-5

ka3=4.0x10^-7

since ka1>ka2,ka2 Ka2 the primary source of H3O+ in the solution will be the 1st ionization so we use it for the calculation

   H3C6H5O7 +H2O<------->    H2C6H5O7- +    H3O+

I     0.145M                                   0             0

c        -x                                       x             x

E    0.145-x                                  x              x

7.5x10^-4=x2/0.145-x     (neglecting x in the denominator)

x2=1.08x10^-4

x=0.01039=[H3O+]=[H2C6H5O7-]

pH=-log(0.01039)=1.98