Show the calculations for determining the equilibrium FeSCN2

Show the calculations for determining the equilibrium [Fe(SCN)]2+concentration forsolution6. Show how you used the Beer-Lambert Law (A= ·l·c), your data, and your determined constant ·l.Remember lis the path length and is 1 cm, and·l is m, the slope of the line.

Solution

FeSCN2+ complexation:-

Fe³⁺ (aq) +SCN^-(aq) <---> FeSCN²⁺

1) Prepare standard solutions of known concentrations.Either one of the Fe3+ or SCN- solution is taken in excess (large concentration) to drive the reaction equilibrium in forward direction.(according to Le chatlier\'s principle).

If [SCN-]<<<[Fe3+] ,so it is assumed that the reaction is driven to completion as it is forward directed due to excess of one of the reactant .(le chatlier\'s principle). and the lesser reactant [SCN-] here, is the limiting reactant

The limiting reagent [SCN-] is completely used up ,and form equal concentration of product, FeSCN²⁺

^[ FeSCN²⁺]equilibrium= [SCN-]initial

You now hve the values of ^[ FeSCN²⁺]equilibriumfor the known standards ,so measure their absorbances and plot the callibration curve between the ^[ FeSCN²⁺]equilibrium and their corresponding Absorbance values.

Using Beer\'s law ,

Absorbance=e*l*C

where e=absorptivity of species(FeSCN2+)

l=path length of light(1 cm)

C=concentration of species (in mg/L)

Absorbance Vs C (as per given data) gives a linear plot of the form y=mx+c ,c=intercept=0,m=slope=el

2) Use the value of el and put it in the equation Concentration(unknown)=Absorbance(unknown)/el to calculate the concentration of unknown solution.