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

To calculate CF and CS in the colorimetric equilibrium study of the complex ion, you will indeed need the absorbance and volume information in addition to the concentrations.

Here's how you can calculate CF and CS:

1. Prepare solutions: Start by preparing solutions with known concentrations of [KSCN], [HNO3], and [FeNO3]. These concentrations will be used to find the equilibrium concentrations of various species.

2. Determine the equilibrium concentrations: Perform the chemical reaction and allow it to reach equilibrium. Measure the absorbance of the solution at a specific wavelength. The absorbance is directly proportional to the concentration of the colored complex.

3. Use Beer-Lambert Law: Apply the Beer-Lambert Law, which states that absorbance (A) is directly proportional to the concentration (C) and the path length (b) traveled by light through the solution. The equation is given as A = εcb, where ε is the molar absorptivity or extinction coefficient specific to the complex.

4. Calculate CF: Use the absorbance measurement at a specific wavelength to determine the concentration of the complex [Fe(NCS)] by rearranging the Beer-Lambert Law equation and solving for CF: [Fe(NCS)] = A / (ε × b).
Then, calculate CF by adding the concentration of [Fe] to [Fe(NCS)].

5. Calculate CS: Since CS is the stoichiometric molarity of thiocyanate ion, you need to consider the equilibrium concentrations of the reactants involved. Use the equation CS = [SCN] + [Fe(NCS)] to calculate CS. [SCN] is the initial concentration of [KSCN] used, and [Fe(NCS)] is the equilibrium concentration of the complex determined from the absorbance measurement.

In summary, to calculate CF, use the Beer-Lambert Law equation and the absorbance measurement to determine [Fe(NCS)], and then add [Fe] to obtain CF. To calculate CS, use the equation CS = [SCN] + [Fe(NCS)], considering the initial concentration of [KSCN] and the equilibrium concentration of the complex.

Make sure to consult your lab manual or ask your instructor for any specific requirements or adjustments in the calculations for your experiment.