Question

  12. In a solution, when the concentrations of a weak acid and its conjugate base are equal,….

[A] the system is not at equilibrium

[B] the -log of the [H⁺] and the -log of the K_a are equal

[C] the buffering capacity is significantly decreased

[D] the buffering capacity is significantly increased

[E] All of the above are true.

13. The concentration of iodide ions in a saturated solution of lead (II) iodide is ________ M.

The solubility product constant of PbI₂ is 1.4 x 10^-8.

[A] 1.4 x 10^-8 [B] 1.5 x 10^-3 [C] 3.5 x 10^-9 [D] 3.8 x 10^-4 [E] 3.0 x 10^-3

14. The solubility of lead (II) chloride (PbCl₂) is 1.6 x 10^-2 M. What is the K_sp of PbCl₂?

   [A] 4.1 x 10^-6 [B] 1.6 x 10^-5 [C] 3.1 x 10^-7 [D] 5.0 x 10^-4 [E] 1.6 x 10^-2

  15. The solubility of manganese (II) hydroxide (Mn(OH)₂) is 2.2 x 10^-5 M. What is the K_sp of

   Mn(OH)₂?

[A] 2.2 x 10^-5 [B] 2.1 x 10^-14 [C] 1.1 x 10^-14 [D] 4.8 x 10^-10 [E] 4.3 x 10^-14

16. Which of these expressions correctly expresses the solubility-product constant for

Ag₃PO₄ in water?

[A] [Ag][PO₄] [B] [Ag⁺][PO₄³⁻] [C] [Ag⁺]³[PO₄³⁻]

   [D] [Ag⁺][PO₄³⁻]³ [E] [Ag⁺]³[PO₄³⁻]³

  17. A solution of NaF is added dropwise to a solution that is 0.0166 M in Ba²⁺. When the

   concentration of F^- exceeds ________ M, BaF₂ will precipitate. Neglect volume changes.

For BaF₂, K_sp = 1.7 ⋅ 10^-6.

[A] 1.0 x 10^-2 [B] 1.0 x 10^-4 [C] 5.1 x 10^-5 [D] 2.5 x 10^-3 [E] 2.8 x 10^-8

18. A solution contains 2.3 x 10^-4 M Ag⁺ and NaI solution is being added drop wise. What

   is the minimum concentration of I^- to begin precipitation of AgI? Ksp (AgI)= 8.3 x 10^-17

   [A] 8.32 x10^-17 M [B] 2.51 x 10^-17 M [C] 3.01 x 10^-15

   [D] 3.51 x 10^-14 M [E] 3.61 x 10^-13 M

Answer 1

12. In a solution, when the concentrations of a weak acid and its conjugate base are equal,….

[A] the system is not at equilibrium

[B] the -log of the [H+] and the -log of the Ka are equal; since pH = pKa + log(caonjugate/acid) and log(1) = 0 so pH = pKa

[C] the buffering capacity is significantly decreased

[D] the buffering capacity is significantly increased

[E] All of the above are true.

13. The concentration of iodide ions in a saturated solution of lead (II) iodide is ________ M.

The solubility product constant of PbI2 is 1.4 x 10-8.

[A] 1.4 x 10-8     [B] 1.5 x 10-3 [C] 3.5 x 10-9   [D] 3.8 x 10-4 [E] 3.0 x 10-3

Ksp = [Pb+2][I-]^2

1.4*10^-8 = S*(2S)^2

4S^3 = 1.4*10^-8

S = ((1.4*10^-8/4)^(1/3) = 0.00151829 M = 1.5*10^-3

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