[navneet]

We are doing a lab, in which we compare colour intensity as the reaction approaches equilibrium for the reaction.

Fe³⁺_(aq)+SCN^-_(aq) <-------> FeSCN²⁺_(aq)

FeSCN²⁺_(aq), which is red colour

And the Mole ratio is 1 to 1 if im correct. And SCN^-_(aq) is limiting reagent and the concentration of SCN^-_(aq) 0.0010 mol/L .

In Class we prepair 5 test tubes, for this sake lets say we prepair two test tubes.

The first test tube is the standard soloution, and the second test tube is different concentration soloution.  Now we put the two soloutions on a projection which passes light through it, and if we look from the top we will see the colours red for both test tubes, but test tube 1 or 2 can be lighter or darker than each other.

Lets say if test tube #1 is lighter than #2, therefore we add more concentration in test tube #1, but keep in mind that in this experiment we dont add or remove concentration in Test Tube #2 for the whole experiment, but we can remove or add concentration in test tube #1 only, adding more concentration will make it darker, and lighter if we remove concentration. Once the colour matches than we record the depth for each Test Tubes in Milimeters.

Now my question is that there are three formulas, I know why two of them works. Note "[ ]" means Mol/L (concentration).

I know why these two work.

[Fe⁺³]_{(equlilbrium)} = [Fe⁺³]_initial - [FeSCN²⁺]_equlilbrium

I think this formula works because the ration of Mols is 1 to 1 for all three, and simply change in concentration gives us the Equlilbrium of Fe ion. Which is what we are doing in this formula calculating change in concentration.

And second formula is [SCN^-]_{(equlilbrium)} = [SCN^-]_initial - [FeSCN²⁺]_equlilbrium

Same for this formula.

Please correct me if im wrong.

Can someone please explain why this formula works.

[FeSCN²⁺]_equilibrium = Depth Ration x [FeSCN²⁺]_std

Where Depth Ration= Depth of of Liquid in Test Tube 1 (standard tube) / Depth of liquid in tube # 2

remeber that depth ration can we different, and is measured in milimeters.  Lets the the depth ration in T.T.  1 is 20 ml and in T.T.2 is 10 ml
we divide these two and multiply it by [FeSCN²⁺]_std

And the value for [FeSCN²⁺]_std is = to 0.0010 mol/L, since SCN -1 is limiting reagent.

Example:  20 ml/10 ml  x  [0.0010] = 0.0020 mol/l

Can anyone explain why this formula works please?

Because I dont understand what does the depth ration has to do with the formula. Actaully I just dont understand the formula.

Thx for reading