Which of the following species is amphoteric? CO_3^2^- HF NH_4^+ HPO_4^2^- None

Question

Which of the following species is amphoteric? CO_3^2^- HF NH_4^+ HPO_4^2^- None of the above are amphoteric. A 0.20 M sodium chlorobenzoate (NaC_7H_4CIO_2) has a pH of 8.62. Calculate the pH of a 0 20 chlorobenzoic acid (HC_7H_4CIO_2) solution. Additional problems: Brown 16.53 -16.66, 16.79 -16.82 7. Using the following K, values, indicate the correct order of BASE strength HNO_2 K_a = 4.0 times 10^-4 HF K_a = 7.2 times 10^-4 HCN K_a = 6.2 times 10^-10 Additional problems: Brown 16.81 and 16.82 8. Calculate the [H^+] in a solution that is 0.17 M in NaF and 0.25 M in HF. (K_a = 7 2 times 10^-4) Additional problems: Brown 17.21 and 17.22 What volume of 0.0100 M NaOH must be added to 1.001 of 0.500 M HOCI to achieve, 1 oh of 8.00? Additional problems: Brown 17.25-17.28 Calculate the pH of a solution prepared by mixing 45.0 ml of 0.183 M KOH and 65 0 - of 0.145 MHCI. Additional problems: Brown 17.39a, 17.40a, 17.41, 17.42, 17 45a 1: Methylamine, CH_3NH_2 has a Kb of 5.0 times 10^-4 What is the pH of a 0.080 M methylamine (CH_3NH_2) solution? If 20.0 ml if a methylamine is titrated with a 0.10 M solution of HCI, what will be tr, of the solution at the equivalence point? What is the pH of the solution at the midpoint? What is the pH of the solution after the addition of 25 ml of HCI? Additional problems: Brown 17.38-17.46

Explanation / Answer

(5) The chemical species that is able to react with both acids and bases is called amphoteric

Here the amphoteric species is (D) HPO42-

(6)

pH = -log[H+] = 8.62 => [H+] = 2.398 x 10-9 M

Kw = [H+][OH-] = 10-14 => [OH-] = 4.168x 10-6 M

C7H4ClO2- + H2O <=> HC7H4ClO2 + OH-

Kb = [HC7H4ClO2][OH-]/[C7H4ClO2-]

Kb = (4.168 x 10-6)2/0.20 = 8.689 x 10-11

HC7H4ClO2 <=> C7H4ClO2- + H+

Ka = [C7H4ClO2-] [H+]/[HC7H4ClO2]

Also Ka x Kb = Kw = 10-14

[H+]2/[HC7H4ClO2] = [H+]2/0.20 = 10-14/Kb

= 10-14/8.689 x 10-11

[H+] = 0.00479 M

pH = -log[H+] = 2.318 = 2.32

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