Respuesta :

The pH of a solution that is 0.50 M in HCOOH is 2.045.

How do we calculate the pH?

pH of the solution will be calculated by taking the negative logarithm of the concentration of H⁺ ion.

Given chemical reaction will be:

                            HCOOH(aq)   ⇄   H⁺(aq)   +   HCOO⁻(aq)

Initial:                         0.50                    0                    0

Equilibrium:              0.50-x                  x                    x

Given that, pKa = 3.75

Ka = [tex]10^{-pKa}[/tex]

Ka = [tex]10^{-3.75}[/tex] = 0.000178

Ka for the above equation will be written as:
Ka = [H⁺][HCOO⁻]/[HCOOH]

Ka = (x)² / (0.50-x)

x is negligible as compared to 0.5, so the equation becomes

0.000178 = (x)² / 0.50

x² = (0.000178)(0.5) = 0.000089

x = 0.009

[H⁺] = 0.009M

pH will be calculated as:

pH = -log(0.009) = -(-2.045) = 2.045

Hence pH of the solution is 2.045.

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