For HCN in water, Ka = 2.0E-10. Calculate the fraction of cyanide that exists as the anion rather than in the molecular form at pH values of 4, 7, and 10.
This is a question on buffers. The equation Ka = [H+] * [CN-]/[HCN] will work here.
You are given ...
The solution explains which area of chemistry this question pertains to and provides an equation that can find the fraction of cyanide existing at the anion (as opposed to in molecular form) at all three pH levels specified.