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An unknown weak acid with a concentration of 0.072 M has a pH of 1.80. What is the Ka of the weak acid

Respuesta :

The value of Ka of the weak acid is 4.47 x 10^-3.

The acids that do not dissociate completely in the aqueous solution and remains in equilibrium are called weak acids. The acid dissociation constant of the weak acid is represented as Ka.

Consider a weak acid HA. Its dissociation reaction will be:

      HA        ----->      H+         +          A-

I    0.072                    0                       0

C     -x                       +x                      +x

E  0.072-x                  x                        x

Calculations:

pH = -log[H+]

1.80 = -log[H+]

[H+] = 0.01585 M

Hence, x = 0.01585 M

The value of Ka is calculated as:

Ka = x^2/0.072-x

= (0.01585)^2/(0.072 - 0.01585)

= 4.47 x 10^-3

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