[BrahmaBull9813]

We conducted an experiment in Chemistry lab titled Colorimetric Determination of an Equilibrium Constant in Aqueous Solution.

We're given the following reaction.

Fe³⁺ (aq) + SCN^- (aq) ⇌ FeNCS²⁺ (aq)


In the midst of instruction for the first part (A) of the experiment, the directions say to calculate the values for the FeNCS²⁺ concentration using the values in 'Table 22.1'.

Solution

|

mL of 2.00 x 10-1 M Fe(NO3)3          in 0.10 M HNO3

|

mL of 2.00 x 10-3 M NaSCN          in 0.10 M HNO3

|

Total volume (mL)

1                   10.00                                      0.00                              50.00
2                   10.00                                      1.00                              50.00
3                   10.00                                      2.00                              50.00
4                   10.00                                      3.00                              50.00
5                   10.00                                      4.00                              50.00
6                   10.00                                      5.00                              50.00

Then, in the chart, it asks for the Initial [SCN^-], M and the Equil. [FeNCS²⁺], M for beakers 1-6. None of the calculations involve experimental data, but just the above table. That's why I feel so puzzled because I could not figure out how to utilize these values to find the calculated results needed to be plugged into the results table.

I understood that there is a dilution factor of 50, so I had to divide the molar concentrations by 50 in order to obtain the Concentrations of Fe(NO₃)₃ and NaSCN, respectively, in 0.10 M HNO₃ solution. I understood how to calculate the Percent Transmittance from the Absorbance values obtained from the Spectrophotometer.

I just can't seem to understand how to figure out the values for the Initial and Equilibrium concentrations. My professor kept giving me hints which I could not use to understand how to use to deduce what the values should be. He kept mentioning the RICE chart and the equation for an equilibrium constant, but refused to explain how to obtain these values.

Given the information above, can someone PLEASE assist me in understanding how to calculate these values and complete this lab experiment?

[Borek]

Not seeing all data and a whole procedure it is hard to say something 100% sure, but you have a large excess of iron present, so it is likely that you are to assume equilibrium is shifted far right.