Answer to Question #239579 in Chemistry for Fatima

Question

What is the pH of the solution given that the concentration of H2PO₄^- is 0.1 and that of HPO₄^2- is 0.066?

Answer 1

Solution:

The Henderson–Hasselbalch equation can be used.

The formula for the Henderson–Hasselbalch equation is: 

pH = pK_a + log([A⁻] / [HA]),

where [A^–] and [HA] are concentrations of the conjugate base and starting acid.

H₂PO₄^– – starting acid

HPO₄^2–– conjugate base

Thus,

[A⁻] = 0.066 M

[HA] = 0.100 M

H₂PO₄^– ⇔ HPO₄^2– + H⁺, pK_a = 7.2

Hence,

pH = 7.2 + log(0.066 / 0.100) = 7.2 + (-0.18) = 7.02

pH = 7.02

Answer: pH = 7.02