Points to consider
Finding an equilibrium constant is a bit different from most experiments in that there are several stages to it. First you have to mix the reagents together, then you have to leave them so that they're undisturbed for a time and finally you have to analyse the mixture to find the concentration of one of the products. You need to think about each of these stages before you start.
How long should the mixture be left so that it can achieve equilibrium?
Where can the mixture be safely left to achieve equilibrium?
What techniques might you use to find the concentration of one of the components of an equilibrium mixture?