Constants Periodic Table Part A Lead thiocyanate, Pb(SCN)2. has a Kip value of 2

Question

Constants Periodic Table Part A Lead thiocyanate, Pb(SCN)2. has a Kip value of 2.00 x 10-5 Calculate the molar solubility of lead thiocyanate in pure water. The molar solubility is the maximum amount of lead thiocyanate the solution can hold Express your answer with the appropriate units. View Available Hint(s) ValueUnits Submit Common-lon Effect Consider the dissolution of AB(s): AB(s) A (aq) +B (aq) Le Chatelier's principle tells us that an increase in either [A or B-] will shift this equilibrium to the left, reducing the solubility of AB. In other words AB is more soluble in pure water than in a solution that already contains A or B ions. This is an example of the common-ion effect. Part B Calculate the molar solubility of lead thiocyanate in 0.600 MKSCN Express your answer with the appropriate units.

Explanation / Answer

A)

At equilibrium:
Pb(SCN)2 <---->     Pb2+     +         2 SCN-  

                     s                  2s      

Ksp = [Pb2+][SCN-]^2
2*10^-5=(s)*(2s)^2
2*10^-5= 4(s)^3
s = 1.71*10^-2 M
Answer: 1.71*10^-2 M

B)
KSCN here is Strong electrolyte
It will dissociate completely to give [SCN-] = 0.600 M

At equilibrium:
Pb(SCN)2 <---->     Pb2+     +         2 SCN-  
                     s                  0.600 + 2s
Ksp = [Pb2+][SCN-]^2
2*10^-5=(s)*(0.6+ 2s)^2
Since Ksp is small, s can be ignored as compared to 0.600
Above expression thus becomes:
2*10^-5=(s)*(0.6)^2
2*10^-5= (s) * 0.36
s = 5.56*10^-5 M
Answer:   5.56*10^-5 M

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