The pH of an acid solution is 511 Calculate the Ka for the m

The pH of an acid solution is 5.11. Calculate the Ka for the monoprotic acid. The initial acid concentration is 0.010 M. X 10 Enter your answer in scientific notation

Solution

Weak monoprotic acid dissociates as

AH +H₂O A- + H₃O⁺

K_a = [A^-][H₃O⁺] / [AH]

Acid is monoprotic therefore

[A^-] = [H₃O⁺] = x

[H₃O⁺] = 10^-pH = 10^-5.11 = 7.76 X 10^-6 M

[A^-] = [H₃O⁺] = x = 7.76 X 10^-6 M

K_a = [x][x] / [AH]

Substitute the value in equation

K_a = [7.76 X 10^-6M][7.76 X 10^-6 M]/ 0.010

K_a  = 6.02 x 10^-9