Answer to Question #307645 in General Chemistry for termite

Question

1.Calculate the pH of a base buffer solution composed of 0.20 M NH₃ and 0.15 M NH₄Cl after the addition of 0.10 M HCl. The K_b of NH₃ at 25^oC is 1.80 × 10^-5.

2.What is the pOH of a buffer solution that is 0.150 M chloroacetic acid and 0.250 M sodium chloroacetate, after the addition of 0.100 M HNO₃? The value of K_a for chloroacetic acid is 1.3 x 10^-3.

Answer 1

1) The following reaction occurs during the addition of acid:

NH₃ + HCl = NH₄Cl

After the addition of acid, the new concentrations of the components will be as follows(assume that the volume of the solution remains unchanged):

С(NH₃) = 0.2 - 0.1 = 0.1 M

С(NH₄Cl) = 0.1 + 0.15 = 0.25 M

For base buffer solution pH = 14 + lgK_b + lg(C_b/C_salt) = 8.86

2) The following reaction occurs during the addition of acid:

ClCH₂COONa + HNO₃ = ClCH₂COOH + NaNO₃

New concentrations of chloroacetic acid and sodium chloroacetate (assume that the volume of the solution remains unchanged) is:

С(ClCH₂COOH) = 0.15 + 0.1 = 0.25 M

С(ClCH₂COONal) = 0.25 - 0.1 = 0.15 M

For acid buffer solution pH = -l gK_a - lg(C_a/C_salt) = 2.886 - 0.221 = 2.664

pOH = 14 - pH = 11.336