2 questions eating me!!!

[Pisiform]

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Hey guys!!! my last resort to this problem is SDN 🙄 . Ok so have trouble with the following questions. I just don't understand why and how to do these questions without putting 2x as stated in TBR Gen, Chem Book pg. 194 Q 28 and Q 29.

Q1 - What is the molar solubility of CaCl2 (s) in 0.01M of NaCl (aq) solution?

Ans: 2.5 * 10^-6

Q2 - What is the molar solubility of Ca(OH)2 in an aqueous solution at pH 13 given that Ksp for Ca(OH)2 is 6.5*10^-6 M^3

Ans: 6.5 * 10^-4

I would really appreciate your input and remember u guys/girls in prayers 😍

 

[Misc]

Q1 - was a Ksp given for CaCl2?

Q2

pH13 = pOH1 so [OH]=0.1M

Ca(OH)2 <-> Ca + 2OH
so given initial concentration of [OH]=0.1 and that x Ca(OH)2 turns into x Ca and 2x OH, we have
Ksp=[Ca]*[OH]^2
6.5*10^-6=x(0.1+2x)^2
assuming x is small compared to 0.1, we get
6.5*10^-6=x(0.1^2)
6.5*10^-6=x*10^-2
x=6.5*10^-4 which is the answer

 

[TheBoondocks]

Hey guys!!! my last resort to this problem is SDN 🙄 . Ok so have trouble with the following questions. I just don't understand why and how to do these questions without putting 2x as stated in TBR Gen, Chem Book pg. 194 Q 28 and Q 29.

Q1 - What is the molar solubility of CaCl2 (s) in 0.01M of NaCl (aq) solution?

Ans: 2.5 * 10^-6

Q2 - What is the molar solubility of Ca(OH)2 in an aqueous solution at pH 13 given that Ksp for Ca(OH)2 is 6.5*10^-6 M^3

Ans: 6.5 * 10^-4

I would really appreciate your input and remember u guys/girls in prayers 😍

I remember this from TBR.

The Ksp of CaCl2 is 2.5e-10. so 2.5e-10=(x of Ca)(2x OH + .01)^2 You assume that the x (molar solubility is insignificant). so 2.5e-10 =x(1e-4)

this gives you 2.5e-6