Question

What is the approximate pH of a 0.10 M solution of a weak acid that has a Ka of 5 x10^-5 M?

Answer 1

Answer:

pH = 2.66

Explanation:

weak acid:

• HA ↔ H+  + A-

∴ Ka = 5 E-5 M = [H+][A-]/[HA]

∴ [HA] = 0.10 M - [A-]

∴ [H+] = [A-]

⇒ Ka = [H+]²/(0.10 - [H+])

⇒ [H+]² + 5 E-5[H+] - 5 E-6 = 0

⇒ [H+] = 2.211 E-3 M

⇒ pH = - Log [H+]

⇒ pH = 2.6553