Question

34. Chromium(III) hydroxide has Ksp 1.6 x 10-30. What is the molar solubility of Cr(OH)3 in a solution whose pH is maintained at 6.00? (A) 1.6 x 10-12 mol L-1 (C) 3.6 х 10-8 mol L-1 (B) 1.6 x 10- mol L-1 (D) 1.6 x 106 mol L-1 35. At 400 K, this reaction has Kp- 8.2 x 10. SO3(g)SO2(g)/ 02(g) What is Kp at 400 K for the following reaction? 2 SO3(g) 2 SO2(g) + O2(g) (B) 8.2 x 104 (D) 2.9 x 10-2 (A) 6.7 x 10-7 (C) 1.6 x 103

Answer 1

34)

use:

pH = -log [H+]

6 = -log [H+]

[H+] = 1*10^-6 M

use:

[OH-] = Kw/[H+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

[OH-] = (1.0*10^-14)/[H+]

[OH-] = (1.0*10^-14)/(1*10^-6)

[OH-] = 1*10^-8 M

pH here is Strong electrolyte

It will dissociate completely to give [OH-] = 1.0*10^-8 M

At equilibrium:

Cr(OH)3 <----> Cr3+ + 3 OH-

   s 1*10^-8

Ksp = [Cr3+][OH-]^3

1.6*10^-30=(s)*(1*10^-8)^3

1.6*10^-30= (s) * 10^-24

s = 1.6*10^-6 M

Answer: D

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