Posted by Abigail on Tuesday, April 15, 2008 at 4:56pm.
Please let me know if my answer to the following question is correct.
Question:
What is the concentration of a weak base if its Kb = 1.4 x 1011 and its pH = 8.75?
Answer:
Converting pH to H^+ concentration using the formula H^+ = 10^ph, therefore 10^8.75 gives an H^+ concentration value of 1.0 x 10^9. Now, using the formula Ka=Kw/Kb and subsitituing in the values (Ka = 1.4 x10^14/1.4 x 10^11) gives 1.0 x 10^3.
Now, subtracting 1.0 x 10^3 from 1.0x 10^9 gives a concentration of 9.9 x 10^4 mol/L

chemistry  DrBob222, Tuesday, April 15, 2008 at 5:34pm
No, I don't think so. First, pH = 8.75 gives (H^+) = 1.77 x 10^9.
Then I would say (OH^) = Kw/(H^+) = ??
Then BOH <==>B^+ + OH^
Kb = (B^+)(OH^)/(BOH) = 1.4 x 10^11
You now have (B^+)=(OH^) = 5.62 x 10^6 and you can solve for (BOH).

chemistry  Abigail, Tuesday, April 15, 2008 at 5:38pm
rats....:)
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