Answer to Question #307369 in General Chemistry for Lawi

Question

1.Given below is the dissociation of NH₃ in water having a K_b value of 1.8 × 10^-5. The reaction started with the equilibration of 0.65 M NH₃. A common ion that is 0.25 M NH₄Cl, was added to the initial solution and waited for some time for the reaction to reach equilibrium once again.

NH_3(aq) + H₂O_(l) ↔ NH₄⁺_(aq) + OH^-_(aq)

Determine the pH of the solution given after the addition of the common ion. The K_w of water is 1.0 × 10^-14.

2.What is the pH of a buffer solution that is 0.350 M ethylamine and 0.200 Methylammonium chloride, after the addition of 0.100 M HNO₃? The value of K_b for ethylamine is 4.7 x 10^-4.

Answer 1

2. pOH = pKb + log₁₀(acid/base)

 

pOH = 3.32 + log₁₀(0.35/0.2)

Addition of HNO₃:

pOH = 3.32 + log₁₀(0.35+0.1/0.2)

pOH = 3.38

pH = 14 – 3.38 = 10.62