Question

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)

Answer 1

a) 3.969

b) 3.489

Step-by-step explanation:

a) Calculate the pk, value of the acid HA

PH of salt hydrolysis

P
`^(H)` = 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