# What is the appropriate way of writing the Iron/thiocyanate equilibrium? I understand the theory, but am struggling to answer the following discussion questions:

(i)
Why isn't this represented by: $\ce{Fe^{3+} (aq) + 3 SCN- (aq) <=> Fe(SCN)3 (aq)}$
Why do we dilute the solution with water?

(ii)
I don't understand what the question is asking, can someone please explain

(iii)
I understand this.

(iv)
I am unsure, can someone suggest a reason.

(v)
I understand this.

(vi)
Constant volume of container?

1. I thought ALL equilibrium reactions needed to be in a closed vessel - so if this experiment was conducted in an open test tube, wouldn't this be an error? How would this affect the accuracy of the results - would it be under/over estimated and why?

The second representation is more accurate because in water there can be no naked'' $\ce{Fe^3+}$ ion; as it goes into solution, iron combines with water to form an ion consisting of a $\ce{Fe}$ atom surrounded by six molecules of water. It is the oxygens that form bonds with the iron atom, in a roughly octahedral arrangement: two oxygen atoms in each coordinate direction, one on either side. The reaction consists of the replacement of one of these coordinated water molecules by the $\ce{SCN-}$ ion; now the iron has bonds to 5 oxygens and 1 nitrogen atom.
The addition of $\ce{H2O}$ to the formula doesn't mean we are diluting the solution with water. It just means we're letting the water that's present anyway play a role in the equation, to reflect reality.
It's not clear to me what they are asking in (ii). The colors change dramatically when you mix $\ce{[Fe(H2O)6]^3+}$ (pale yellow) with $\ce{SCN-}$ (colorless); the result is deep red. Perhaps some context will help. Read the discussion of the reaction in the text to see what they say about color intensity.