Question

#9 and #10 Thank you

solubility of the slightly soluble salt The solubility of AgCl is the same in a 1.0 M NH, solution vs. in pure water because the Ksp of AgCl is a constant at 25°C. D) 9. Calculate the molar solubity of AgBrts) in 0.500 M NH, at 25°C. Kup of AgBr is 1.8 x 10-5, K of Ag(NHs)2" is 1.7 x 10 A) 8.7 x 104 M B) 1.2x 10-3 M C) 4.2 x 10-7 M D) 7.7 x 10-7 M 10. Which of the following compounds, when added to a saturated solution of zinc carbonate, will decrease the solubility of zinc carbonate? Kap of ZnCOs is 1.0 x 10-10, K of Zn(CN) is 4.2x 1019 A) HIl(aq) B) Na COs(a) C) NaCN(aq) D) NaCl(aq)

Answer 1

9.

AgBr(s) <==> Ag⁺(aq) + Br^-(aq);          Ksp = 1.8 x 10^-13 ----------------(1)
Ag⁺(aq) + 2NH₃(aq) <==> [Ag(NH₃)₂]⁺   Kf   = 1.7 x 10⁷   ----------------(2)
------------------------------------------------------------------------------------------.
AgBr(s) + 2NH3(aq) <==> [Ag(NH₃)₂]⁺(aq) + Br^-(aq); Kc = Ksp x Kf

So,
Kc = (1.8 x 10^-13) x (1.7 x 10⁷)
     = 3.06 x 10^-6

But,

Kc = [Ag(NH₃)₂⁺] [Br^-] / [NH₃]²
3.06 x 10^-6 = (x)(x) / (0.5 - 2x)²
3.06 x 10^-6 = x² / (0.5)²
x² = (3.06 x 10^-6) x (0.25)
x² = 7.65 x 10^-7
x = 8.75 x 10^-4

So, answer is option (A) 8.7 x 10^-4 M

10.

ZnCO₃ will dissociate as follows;

ZnCO₃ <==>   Zn²⁺    + CO₃^2-(aq);         

When Na₂CO₃ is added, it will dissociate as follows;

Na₂CO₃ <==>   2 Na⁺    + CO₃^2-(aq);

So, more CO₃^2-(aq) formed will react with Zn²⁺ to produce back ZnCO₃.

So, answer is option (B) Na₂CO₃.