Question

15.) a.)In the laboratory, a general chemistry student measured the pH of a 0.376 M aqueous solution of nitrous acid to be 1.872.

Use the information she obtained to determine the K_a for this acid.

K_a(experiment) =

b.)In the laboratory, a general chemistry student measured the pH of a 0.376 M aqueous solution of nitrous acid to be 1.870.

Use the information she obtained to determine the K_a for this acid.

K_a(experiment) =

c.)In the laboratory, a general chemistry student measured the pH of a 0.376 M aqueous solution of hydrocyanic acid to be 4.928.

Use the information she obtained to determine the K_a for this acid.

K_a(experiment) =

Answer 1

15)

a) [HNO2] = 0.376 M

pH = -log[H+] = 1.872

[H+] = 0.01343 M

[H+] = [A-] = 0.01343 M

[HNO2] at equilibrium = 0.376 - 0.01343 = 0.3626 M

Ka (experimental) = [H+][A-]/[HA]

                             = (0.01343)^2/(0.3626)

                             = 4.97 x 10^-4

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b) [HNO2] = 0.376 M

pH = -log[H+] = 1.870

[H+] = 0.01350 M

[H+] = [A-] = 0.01350 M

[HNO2] at equilibrium = 0.376 - 0.01350 = 0.3625 M

Ka (experimental) = [H+][A-]/[HA]

                             = (0.01350)^2/(0.3625)

                             = 5.03 x 10^-4

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c) [HCN] = 0.376 M

pH = -log[H+] = 4.928

[H+] = 1.18 x 10^-5 M

[H+] = [A-] = 1.18 x 10^-5 M

[HCN] at equilibrium = 0.376

Ka (experimental) = [H+][A-]/[HA]

                             = (1.18 x 10^-5)^2/(0.376)

                             = 3.70 x 10^-10