Question

A 1.0 M H2S solution has a pH = 3.75 at equilibrium. What is the value of Ka?

Answer 1

scientific notation on the calculator page, when youre in 0.00000000316390874 just click enter, it does it for you

Answer 2

Ka = 3.16 x 10⁻⁸.

Step-by-step explanation:

• We know that: pH = -log[H⁺],

3.75 = -log[H⁺].

log[H⁺] = -3.75.

∴ [H⁺] = 1.78 x 10⁻⁴ M.

• Also, we have that: [H⁺] =
  `√(Ka.C)`

where, Ka is the dissociation constant of the acid,

C is the concentration of the acid (C = 1.0 M).

∴ 1.78 x 10⁻⁴ M = √(Ka)(1.0 M),

by squaring the both sides:

∴ (1.78 x 10⁻⁴ M)² = (Ka)(1.0),

∴ Ka = 3.16 x 10⁻⁸.