[jonjon1324]

A solution of hydrogen cyanide, HCN, has a 0.025 M concentration. The cyanide ion concentration is found to be 3.16 x 10^-6 M

--What is the concentration of nonionized HCN in the solution?

How am I supposed to find that? Doesn't it already give it? 0.025 M wouldn't be it? What does it mean by..nonionized? Lol.

[Borek]

Write reaction equation for HCN dissociation. 0.025M is so called analytical (or formal) concentration - it sums both dissociated and undissociated HCN.

[shelanachium]

And HCN is a VERY weak acid!

[constant thinker]

If you start with what Borek said you get:

HCN_(*) --> H⁺_(aq) + CN^-_(aq)

*It's technically a liquid at room temp but the boiling temp is so close to room temp and it's such a volatile compound that I'm not going to label it as a liquid or a gas.

As you can see, for ever one mole of HCN you get you get one mole of CN^-. This makes your life simple and all you have to do is subtract the concentration of CN^- ions from the total concentration of HCN (the .025M). This should give you the concentration of undissociated HCN.

It becomes more complicated with other compounds like say citric acid [C₃OH₅(COOH)₃] for multiple reasons.