Answer to Question #335086 in General Chemistry for Ana

Question

A. Calculate the pH of a buffer made from 0.28 M HNO2 and 0.23

M NO2-. The ka for HNO2 is 4.6 x 10-4.

B. What is the pH of the solution containing 0.20 M NH3 and 0.15

M NHACI?

Answer 1

А. pH = pK_a + log A/HA

pKa = logK_a = log 4.6•10^-4 = 3.34

pH = 3.34 + log (0.23/0.28) = 3.25

B. K_b (NH₃) = 1.8•10^-5 pK_b= 4.74

pOH = pK_b - log (NH₄Cl/NH₃)

pOH = 4.74 - log(0.2/0.15)= 4.62

pH = 14 - pOH = 14 - 4.62 = 9.38