Question

the Ka of HClO is 3.0x10^-8 at 25C. calculate pH of a .0385

10) The K of hypochlorous acid (HCIO) is 3.0x10*at 25.0 °C. Calculate the pH of a 0.0385 M hypochlorous acid solution. A) 1.41 B) 8.94 C) 4.47 D) 7.52 E) -1.41 Answer: C 11) Determine the pH of a 0.35 M aqueous solution of CH, NH, (methylamine). The K, of methylamine is 4.4x104 A) 10.00 B) 3.86 C) 12.09 D) 1.96 E) 13.24 Answer: C

Answer 1

10)

Since, HClO is weak acid. Then, [H+] is given by below equation;

[H+]^2 = [HClO] * Ka

[H+]^2 = 0.0385 * 3 * 10^-8

[H+] = 0.00003398 M

pH = - log [H+] = - log (0.00003398) = 4.47 .... Answer

11)

Methyl amine is weak base. Hence, [OH-] will be given by below equation;

[OH-]^2 = [CH3NH2] * Kb

[OH-]^2 = 0.35 * 4.4 * 10^-4

[OH-] = 0.0124 M

pOH = - log (OH-) = - log (0.0124) = 1.906

pH = 14 - pOH = 14 - 1.906 = 12.09 ....Answer