1. Use the Henderson-Hasselbalch to calculate the pH:
pH = pKa + log ( moles of CN�?/SUP> / moles of HCN)
Use Volume X Molarity to get the moles of CN�?/SUP> and HCN. You can divide them by the total volume to get the molarities, but in the ratio in the HH equation, this volume cancels (since the mole values in the numerator and denominator are each divided by this same volume), leaving just the ratio of the moles, which is why I wrote it that way.
Once you have the pH, you can calculate [H+] (which is the same thing as [H3O+] in aqueous solution) using [H+] = 10–pH.
2. That's right, just plug into the HH equation and solve for the ratio [CH3CO2�?/SUP>] / [CH3CO2H]. 
Steve
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