[Bioinorganic78]

I have an analytical chemistry exam on Monday and was given a practice test, but the practice test has no solutions. I did the problems and would like to confirm I did them right, or what I did wrong if I didn't so I know if I am studying right for the test.

1. Calculate the molar ratio of ethylamine (CH3CH2NH2) to the ethylammonium (CH3CH2NH3+) in a solution with a pH of 10 pKa for CH3CH2NH3+ is 10.6
pH=pKa + log([Base]/[Acid])
10=10.6 + log(x)
-0.6=log(x) -> 10^x=-0.6
x=.25= 1/4   1/4 ratio of ethylamine/ethylammonium

Thank You for any help.

2. Estimate Solubility of Mg(OH)2 at pH 12. Ksp = 6*10^-10
pH=12 -> pOH=2
[OH-]=10^-2 M
Ksp=[Mg2+][OH-]^2
6.0*10^-10=x(0.01)^2
x=6.0*10^-6 M

3. Calculate pH of 0.05 M solution of potassium hydrogen carbonate. Pk1= 6.35 Pk2=10.33
pH=(Pk1+Pk2)/2
pH=(6.35+10.33)/2= 8.34

4. Estimate molarity of silver ions Ag+ in a mixture that contains AgCl and 10^-3 M KCl. Ksp AgCl = 1.8*10^-10
Ksp=[Ag+][Cl-]
1.8*10^-10=[Ag+][.001+x] Assume x is small so negligible
1.8*10^-10=.001[Ag+]
[Ag+]= 1.8*10^-7 M

[Borek]

Just skimmed, looks OK.