m shom sig figs, and units, bullet often deducted for long drown helpful in will

Question

m shom sig figs, and units, bullet often deducted for long drown helpful in will be ou is that are not meth should be in bullet format points nations). You have ses minutes. Arns or the solubility product constant, K for strontium sulfate. srso. is Z6xua The solubility product L for fluoride, srF, x 10 at 25 o c? is the olan solubility of Srso4 in Pure water (X) 183 g. 7 A 10 or Fz What is the mo solubility of srF, in pure water at 25 orc? 7.2 x10 x containing 0.020 mole of F 2 X 10 to 1o -stirred on materially affect the solution of Sr(NO,) is added slowly L of a solution does not and 0.10 male 25.0 C. ou may assume that added sroNO) 0.0 20 m 01 F total volume of the system.) Justify. h SP vino 204 i Which salt precipitates first? Q U .10 -3 002 2.4 x 10 020 x 10 0.10 M s64 becausc its Ksp 13 gr carer many F bigger me Ksp, me more so lub ic ir is. s- 8.7 x 10 4 M What is the concentration of strontium ion, Sr 2, in the solution when the first precipitate begins to form? 7 x 10 l, l 1 X10

Explanation / Answer

1. (a) molar solubility of SrSO4 in pure water

with x amount of salt in solution

Ksp = [Sr^2+][SO4^2-]

7.6 x 10^-7 = x^2

x = 8.72 x 10^-4 M

(b) molar solubility of SrF2 in pure water

with x amount of salt in solution

Ksp = [Sr^2+][F-]^2

7.9 x 10^-10 = (x)(2x)^2

x = 5.82 x 10^-4 M

(c) (i) the salt having lowest Ksp value is least soluble in solution and thus would precipitate first out of the solution. Thus, SrF2 would precipitate first.

(ii) [Sr2+] when SrF2 precipitates = Ksp/[F-]^2

                                                      = 7.9 x 10^-10/(0.02)^2     

                                                      = 1.975 x 10^-6 M

2. For NH3 + H2O <==> NH4+ + OH-

a. Equilibrium constant Kc = [NH4+][OH-]/[NH3]

b. pH of 0.018 M NH3

[OH-] = 5.6 x 10^-4 M

pOH = -log[OH-] = 3.25

pH = 14 - pOH = 10.75

c. Kb = (5.6 x 10^-4)^2/(0.018)

         = 1.74 x 10^-8

d. % ionization = 5.6 x 10^-4 x 100/0.018 = 3.11%

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