Question

it has been found that the pH of 0.01M solution of an organic acid is 4.15 calculate the concentration of the anion the ionization constant of the acid and its pka.​

Answer 1

Heya mate Bon Jour

Here is ur answer

concept :- organic acids are weak so, dissociate as HA <=> H+ + A-

so, Ionisation constant , Ka = [H+][A-]/[HA]

you can see that ,

for finding Ka we have to require [H+] and [A-]

[H+] , we can find by using the Arrhenius formula, pH = -log[H+]

and [A-], we can find by using the equation

HA <=> H+ + A-

then, calculate Ka and find pKa by using formula pKa = - logKa

HA <=> H+ + A-

pH = -log[H+]

4.15 = -log[H+] => log[H+] = -4.15

log[H+] = \overline {5}.85log[H+]=

5

.85

[H+] = 7.079 × 10^-5 M

hence, [A-] = 7.079 × 10^-5 M

Ka = [ H+][A-]/[HA]

= (7.079 × 10^-5)(7.079 × 10^-5)/0.01

= 5011.22 × 10^-10

= 5.01122 × 10^-7

= 5 × 10^-7 M

pKa = -logKa

= - log(5 × 10^-7)

= 7 - log5 = 7 - 0.699 = 6.301

hence, pKa = 6.301

Hope it helps

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