Part A The removal of an ion is sometimes considered to be complete when its con

Question

Part A

The removal of an ion is sometimes considered to be complete when its concentration drops to 1.00×106 M. What concentration of hydroxide would cause Y2+ to "completely" precipitate from a solution?

Express your answer with the appropriate units.

Part B

At a pH of 10.5, arrange the solutions containing the following generic hydroxides in order of decreasing concentration of the cation remaining in the solution (i.e., in order of increasing completeness of precipitation).

Rank from highest to lowest cation concentration. To rank items as equivalent, overlap them.

The hydroxide ion has the formula OH. The solubility-product constants for three generic hydroxides are given here.

Use these values to answer the following questions.

Explanation / Answer

Ksp of Y(OH)2     2.4*10^-10

[Y^2+]     = 1*10^-6 M

Y(OH)2 -------------> Y^2+ (aq) + 2OH^-

   Ksp   = [Y2^+][OH^-]^2

2.4*10^-10 = 1*10^-6 *[OH^-]^2

[OH^-] ^2     = 2.4*10^-10/1*10^-6     = 2.4*10^-4

[OH^-]      = 1.55*10^-2 M

B. PH = 10.5

   POH   = 14-PH

             = 14-10.5   = 3.5

POH = 3.5

-log[OH^-] = 3.5

[OH^-]   = 10^-3.5 = 0.00032M

XOH -------------> X^+ (aq) + OH^- (aq)

   Ksp = [X^+][OH^-]

1.4*10^-8 = [X^+] *0.00032

[X^+]    = 1.4*10^-8/0.00032   = 4.375*10^-5 M

Y(OH)2 -----------> Y^2+ (aq) + 2OH^-

Ksp = [Y2+][OH^-]^2

2.4*10^-10    = [Y2^+] *(0.00032)^2

[Y2+]      = 2.4*10^-10/(0.00032)^2   = 0.00234375M

Z(OH)3 --------> Z^3+ (aq) + 3(OH)^-

   Ksp = [Z^3+][OH^-]^3

8.6*10^-15 = [Z^3+]*(0.00032)^3

[Z^3+]      = 8.6*10^-15/(0.00032)^3   = 0.00026M

y^2+]>[Z^3+] > [X^+] increasing order of conc of ions

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