# Equilibrium chem lab (FeSCN2+)

1. Mar 1, 2010

### mill0132

1. The problem statement, all variables and given/known data

Chem lab on equilibrium. We added the same amount of Fe(NO3)2 (5ml) to varying amounts of KSCN and used a given Beer's law and absorption data to calculate concentration of FeSCN2+ and then calculate the Eq. constant (K).

I calculated the Eq. constant, but I'm stuck on two follow up questions:

Consider the equation Fe+3(aq) + SCN(-)(aq) <---> FeSCN 2+

Which ion (Fe3+) or SCN (-) is never in excess? Why?
What experimental conditions are needed to ensure "all" SCN(-) is present as FeSCN2+

2. Relevant equations

The intro we were given in our lab manual described the instability of Fe2+ in water (how it forms Fe3+). Also described the colors of Fe and FeSCN2+. Also defined complex ions and oxidation states.

3. The attempt at a solution

I don't understand how I would know which ion is limiting. We used varying amounts of KSCN and kept the amount of FeNO3 consistent. The stoichiometry would indicate it's a 1:1 ratio. According to the calculations I did for one trial, I end up with fewer moles of SCN(-) at equilibrium, so does that mean it's limiting?

Any guidance on how to figure this out would be appreciated.