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)



Thanks!!

Answer 1

a) 3.969

b) 3.487

Step-by-step explanation:

Given data:

m = 0.27 M

pH = 8.7

a) Calculate PKa of acid HA

pH value = 1/2 ( Pkw + Pka + log C )

8.7 * 2 = 14 + log C + Pka

17.4 = 14 + log ( 0.27 ) + Pka

∴Pka = 17.4 - 14.5686 = 3.9686 ≈ 3.969

b) Calculate the pH of solution

pH = pKa + log ( salt / acid )

= 3.9686 + log ( 0.1 / 0.3 )

= 3.487