Sep 29, 2019
70
21
Status
  1. Pre-Pharmacy
been working on this problem all day and it doesn't make any sense to me

"find the molar solubility of calcium hydroxide in a solution buffered at each of the following pH's"

a. ph=4

b. ph=7

c. ph=9


Here's what I did for the first part

ph=4 , pOH=10

[OH] = 1.0E-10

Ca(OH)2 ---> Ca+2 + 2OH-
I - 1.0E-10M
C +x 1.0E-10M+2x
E x (1.0E-10M + 2x)^2

Ksp = 4.68E-6

I can plug in these values directly and wont get a reasonable answer for x

I have also figured that since the Ksp is orders of magnitude greater than the initial hydroxide concentration we can ignore it and thus assume its just the same as aqueous


the answer should be: 5*10^14M





wasted 5 hours of my life on this... hate myself
 
D

deleted936470

ICE? ew. don't.
Ksp @ 25°C = 5.02×10^–6 & molar solubility (s) of Ca(OH)2*[OH⁻] = 10^(pH - 14)
Ksp = s * (10^(pH - 14))^2 = s * 10^(2*pH - 28)
s = Ksp / 10^(2*pH - 28) = Ksp * 10^(28 - 2*pH)
for example, at neutral pH
s = 5.02*e–6*10^(28 - 2*7) = 5.02*e–6*10^(14) = 5.02*e8 mol/L
 

PlsLetMeIn21

2+ Year Member
Dec 5, 2017
695
452
Status
  1. Pre-Medical
It's all in the bigger picture with your question.

Ksp = [Ca2+][OH-]^2, so [Ca2+] = Ksp/[OH-]^2 where [Ca2+] is your molar solubility.

a) molar solubility = Ksp/(10^-10)^2 = Ksp x 10^20 = 5 x 10^-6 x 10^20 = 5 x 10^14

b) molar solubility = Ksp/(10^-7)^2 = Ksp x 10^14 = 5 x 10^-6 x 10^14 = 5 x 10^8

c) molar solubility = Ksp/(10^-5)^2 = Ksp x 10^10 = 5 x 10^-6 x 10^10 = 5 x 10^4
 

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.
About the Ads