Calculating pH of a solution?

[bearingseat]

I'm having trouble working these two problems, please help with the steps:

Calculate the pH of 233 mL of a saturated calcium hydroxide solution. (Answer is 12.37)

Calculate the mass (mg) of calcium hydroxide that will dissolve in 73 mL of a solution that has a pH = (12.35). [Answer should be 70 mg]

[Red Iron Crown]

Welcome aboard, bearingseat!

Not really a KSP question, moving this to the Science Labs and giving it a more descriptive title.

[K^2]

First of all, "Having trouble with," and "Do my homework for me," are different in that you show us how far you've gotten with your own attempt. Then we can help you out.

Second, there is a lot of missing data here. What other information are you given on C(OH)₂? You might have something like pK_b, solubility, etc. I'm getting slightly different number for pH, for example, and it might be just the matter of me using tables for different temperature. So you'll need to share whatever you're given on this substance.

[Hcube]

Pretty much impossible without any other data... It looks like Ca(OH)2 is a double acid so you should know what couple you are working with. It also looks like it is a weak acid but i can't really tell for sure... that should be given data, along with solubility values. Then the pKa of the couple you are working with are always good to have. Then, pH=-log© or pH=-pKa + log( [base]/[acid] ) should do the job....?

[YNM]

The later question is easy - get molar mass of Ca(OH)2, then the [OH-] out of the pOH (you should know this anyway), then as Ca(OH)2 is strong base, get the molarity of Ca(OH)2. You can work it out yourself.

The former is a bit harder - you lacked the Ksp of Ca(OH)2. One search gives a Ksp of 5.5*10^(-6), you should be good to go I guess.

[K^2]

The later question is easy - get molar mass of Ca(OH)2, then the [OH-] out of the pOH (you should know this anyway), then as Ca(OH)2 is strong base, get the molarity of Ca(OH)2. You can work it out yourself.

Strong base assumption gives pH higher than the answer. And if you look up literature values for pK_a, it seems to indicate reason why. I've gotten pretty close to the answer with numbers from Wikipedia, but not close enough to be sure that they are the same values as given for the problem.