Posted by **Katie** on Thursday, September 13, 2012 at 8:30pm.

I'm doing a chemistry lab called colorimetric equilibrium study of a complex ion. But I just have one question which is how to obtain CS which is the total stoichiometric molarity of thiocynate ion and CF which is iron (III) iron.

Fe+3 + SCN --> Fe(NCS)^+2

Fe(NCS)^+2 + SCN ---> Fe(NCS) (SQUARED ON THE BOTTOM OF (NCS)

Fe(NCS)^-2 (SQUARED ON THE BOTTOM OF (NCS) BUT BY A FACTOR OF 5

+ SCN ---> Fe(NCS)^-3 (SQUARED ON THE BOTTOM OF (NCS) BUT BY A FACTOR OF 6

This lab is stating CS AND CF can be expressed as the sum of the equilibrium concentrations of the various species.

CS = [SCN] + [Fe(NCS)]

CF = [Fe] + [Fe(NCS)]

Concentration:

[KSCN]= 0.002 M

[HNO3] = 0.5 M

[FeNO3] = 0.1 M

Would I need the absorbance and volume to calculate CF and CS? If so, how do I calculate CF and CS? I was wondering the concentrations would equal to [SCN] and etc but I believe I'm wrong since the absorbance has to be used in order to calculate CF and CS.

thank you very much for any help