A 20.0 mL of 0.27 M solution of the salt NaA has a pH of 8.70. a) Calculate the pk, value of the acid HA.

(Correct to 3 sig. fig)

b) Calculate the pH of a solution containing 0.3 M HA and 0.1 M NaA.

(Correct to 3 sig. fig)

a) 3.969

b) 3.489

Explanation:

a) Calculate the pk, value of the acid HA

PH of salt hydrolysis

P = 1/2 ( pkw + pka + logC )

8.7 * 2 =  14 + log ( 0.27 )  + Pka

∴ Pka = 3.9686  ≈  3.969

b) Calculate the PH of a solution containing 0.3 M HA and 0.1 M NaA

PH = Pka + log ( salt / acid )

    = 3.9686 + log ( 0.1 / 0.3 )

    =  3.9686 - 0.48  = 3.489

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