# chemistry

Hi DrBob, I was wondering if you can help me with a few questions? If you can I would truly appreciate your time

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1. post away. One question per post and tell me your best guess or explain why you don't know your next step.

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posted by DrBob222
2. What is the Ksp of aluminum hydroxide when dealing with a saturated solution of aluminum hydroxide, and the concentration of aluminum ion is 2.4 x 10^-8 mol/L.

DrBob, could you please write down the answer only I want to see if I can get to it myself. I am asking this becuase I forgot to bring home the answer sheet to my questions from school.

Thank you so much

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posted by MikeSo
3. The answer I get on my calculator, with all the digits, is 8.95795 x 10^-30 which would round to 9.0 x 10^-30 to two s.f.

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posted by DrBob222
4. Yes! This is the value I got as well!

In a saturated solution of PbBr2, the concentration of Br^-1 is 8.2 x 10^-2 mol/L. What is the [Pb^2+] in mol/l?

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posted by MikeSo
5. OK. for this one only. Why? We would rather check your answers (and let you do the typing) instead of us doing all the typing and you checking your answers. There is another reason, also. If we see how you work the problem we may pick up on some mistake you are making in your thought process. The answer for Ksp for PbBr2 is 2.7568 x 10^-4 which would round to 2.8 x 10^-4 to two s.f.(based on the solubility you listed in the problem.)

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posted by DrBob222

I have a question about Ksp though. Say you have a Ksp value of 1.9 x 10^-8 and 1.8 x 10^-5. Which Ksp would be more soluble?

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posted by MikeSo
7. Never mind I found the naswer---the higher the solubility product, the higher the Ksp value

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posted by MikeSo
8. You need to think this through. You may NOT look at Ksp and determine that one salt is more soluble than another. Let me give you an example.
For AgCl, Ksp = 1.82 x 10^-10
Solubility = sqrt (1.82 x 10^-10) = 1.35 x 10^-5 M.

Now look at the solubility of Ag2CrO4.
Ksp = 1.1 x 10^-12
Solubility = 4x^3 = 1.1 x 10^-12
Solubility = 6.5 x 10^-5 M.
Note that the smaller Ksp of Ag2CrO4 gives a larger solubility (about 6 times larger). So the Ksp will not allow you to estimate which salt is more soluble AND more soluble salt will not always give you larger Ksp.
IT is OK to compare the same type formula; i.e., comparing Ksp for BaSO4 and AgCl is OK since both are 1:1 salts. The reason it didn't work in the example I used is because AgCl is a 1:1 salt while Ag2CrO4 is a 2:1 salt.
So compare Al(OH)3 and any other M(OH)3 OR compare Zn(OH)2 with Ba(OH)2 or Sr(OH_2 OR BaSO4 and AgCl but you can't mix them and get a reasonable answer.

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posted by DrBob222
9. Read my post to your other questions. This statement isn't exactly true.

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posted by DrBob222

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