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

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 Ka 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 Ksp 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 Ksp 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, Ksp = 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

Explanation / Answer

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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