If the concentration of KCN at the equivalence point is 0.1M and the Ka for HCN is 6.2*10^-10 find the pH at the equivalence point.

The reaction is between KOH and HCN
From my understanding I have to do a stoichiometric calculation and then use the Henderson-Hasselback equation to find pH. Is this correct?

Is the equation for the stoichiometry as follows:
HCN+ H2O --> H30+ + CN- ????
Does the 0.1M concentration of KCN represent the end point of the CN- concentration?

Is it possible to calculate the pH with only the limited information?

I believe you're on the wrong track.

This is a hydrolysis equation; i.e., at the equivalence point of an acid/base titration, you are left with the salt and water. The salt hydrolyzes (unless it is the salt of a strong base/strong acid such as NaCl, KCl, KBr etc).
......CN^- + HOH ==> HCN + OH^-
I.....0.1.............0.....0
C.....-x..............x.....x
E....0.1-x............x.....x

Kb of CN^- = (Kw/Ka of HCN)= (x)(x)/(0.1-x)
Solve for x = (OH^-). Convert to pH.

To find the pH at the equivalence point, you are on the right track by considering the stoichiometry of the reaction and using the Henderson-Hasselbalch equation.

First, let's establish the balanced equation for the reaction between KOH and HCN:
HCN + KOH → H2O + KCN

The balanced equation you provided, HCN + H2O → H3O+ + CN-, represents the dissociation of HCN in water, but in this case, we are dealing with the neutralization of HCN by KOH.

Now, let's consider the equivalence point. At the equivalence point, the moles of KOH added are equal to the moles of HCN present initially. This means that all the HCN has been neutralized, leaving only the salt, KCN, in solution.

Given that the concentration of KCN at the equivalence point is 0.1 M, we can assume that the concentration of CN- ions is also 0.1 M, since KCN dissociates into K+ and CN- ions in water.

However, we don't have direct information about the HCN concentration at the equivalence point. To calculate the pH at the equivalence point, we need to know the initial concentration of HCN and the volume of KOH solution added up to the equivalence point.

Without this information, it is not possible to calculate the exact pH at the equivalence point. You would need to know either the initial concentration of HCN or the volume of KOH solution added, in addition to the Ka of HCN, to determine the pH.

In summary, the information provided is not sufficient to calculate the pH at the equivalence point.