What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of 0.050 M NaCN? Assume that the volumes of the solutions are additive and that Ka = 4.9 × 10-10 for HCN.

2.  What is the [CH3CO2-]/[CH3CO2H] ratio necessary to make a buffer solution with a pH of 4.44? Ka = 1.8 ×10-5 for CH3CO2H.
For this one do I just use the Hasselbaclch equation?

Thanks again..