[Vadym]

So, I'm working on some supplemental questions [to boost my mark up to an A for the term], and I've always been terrible at application questions.

Consider the following solution equilibrium reaction:
Fe³⁺_(aq) + SCN^-_(aq) <--> FeSCN²⁺_(aq)

Data was collected on adding various reagents to this system.

KNO_3(aq) = no change
Fe₂(SO₄)_3(aq) = solution darkens
KOH_(aq) = solution lightens
Na₂SO_4(aq) = no change

The question is, for each reagent, which ions are spectator ions and which ions caused the color change?

Now, I remember we had a lab where the temperate was the factor, making the solution lighter and darker in colder and warmer temperatures. It was so long ago, that this is literally all I remember.

Thank you for the help, and also, if you could explain why this happens as opposed to just the answers. Who knows when this question will show up on the provincial?

[Arkcon]

For starters, make a balanced ionization reaction for each one of the added reagents.  There are at least two exact similarities, so you'll have worked out the answer already.

[Vadym]

Thankyou, but this is actually part of the problem. When something is added to the system, what would the eq look like? For example, if D is added to A+B -> C, where would fit in for the balanced ionization reaction?

[Arkcon]

OK, a balanced ionic equation can be considered a decomposition reaction that occurs in aqueous solution:

For example:
Fe₂(SO₄)₃(aq) --> 2 Fe³⁺(aq) + 3 SO₄^2-(aq)

Now adding this changes the color of the solution.  Why?  And what would (possibly?) be just a spectator?

[Vadym]

Alright, so let me take a swing here.

The increased Fe³⁺ concentration in the eqm solution pushed the reaction to the right, creating more product, which in turn created the darker color?