The pH of 0.15 mol/L of hydrocyanic acid is 5.07. Calculate Ka of hydrocyanic acid.
Chemistry - DrBob222, Saturday, November 26, 2011 at 6:41pm
Convert pH to (H^+). It's approximately, but you need to do it exactly, 9E-6
...............HCN ==> H^+ + CN^-
Ka = (H^+)(CN^-)/(HCN)
Substitute from the ICE chart and solve for Ka.
Chemistry - Brandon, Saturday, November 26, 2011 at 7:24pm
How do you calculate the [H^+] and where did you get the -1E-6 from?
Chemistry - DrBob222, Saturday, November 26, 2011 at 7:33pm
pH = -log(H^+)
5.07 = -log(H^+)
-5.07 = log(H^+)
(H^+) = 8.51E-6
Note that at the top of the page I estimated the (H^+) to be 9E-6M and noted that you should calculate it more accurately. Then I substituted into the ICE chart and I used 1E-6. That was a typo but since it was just an estimate it doesn't make much difference. You should substitute 8.51E-6 for (H^+).