Answer to Question #337775 in General Chemistry for soph

Question

4. What mass of CuI is present in a 1.2 L saturated solution at 25°C? Ksp = 1.3 x10-12 (5 marks)

5. Will a precipitate form when 125 mL of 4.0 x 10-2 M of CaCl2 is added to 175 mL of 2.9 x 10-2 M of NaOH? Ksp of Ca(OH)2 = 4.8 x 10-6. Show the dissociation equation for the possible precipitate and all formulas. (10 marks)

Answer 1

5.Ca(OH)₂ <---> Ca²⁺ + 2OH^-

Ksp = 4.8•10^-6 = [Ca²⁺][OH^-]²

And thus we must work out the concentrations with respect to Ca²⁺and OH^- and determine the initial ion product........Q

[Ca²⁺] = Moles of calcium ion / volume of solution = (0.125 L • 4.0 x 10^-2 M) / (0.125 L + 0.175 L) = 0.117 M

[OH^-]² = Moles of hydroxide ion / volume of solution = (0.175 L • 2.9 x 10^-2 M)/(0.125 L + 0.175 L) = 0.017 M

And the ion product 

Q = [Ca²⁺][OH^-]² = 0.117 • (0.017)² = 3.38x10^-5

Since K_sp > Q, precipitation SHOULD NOT occur