Part I:  Preparation of a standard absorption curve for FeSCN+2

Standard	0.20M Fe(NO3)3	0.0020 M KSCN	0.100M HNO3	[FeSCN+2]	Absorbance
A	10.0 mL	0.0 mL	15.0 mL	0	0
B	10.0 mL	1.0 mL	14.0 mL	M	0.343
C	10.0 mL	1.5 mL	13.5 mL	M	0.518
D	10.0 mL	2.0 mL	13.0 mL	M	0.706
E	10.0 mL	2.5 mL	12.5 mL	M	0.860
F	10.0 mL	3.0 mL	12.0 mL	M	1.130

 

EQUATION:

Y : 4572.1x – 0.0068 | 

 

Part 2: Measuring Equilibrium

Test Solution	0.0020 M Fe(NO3)3	0.0020 M KSCN	0.10 M HNO3	Initial [Fe+3]	Initial [SCN–]	Absorbance	Equilibrium [FeSCN+2]*
I	5.0 mL	0	5.0 mL	M	0	0	0
II	5.0 mL	1.0 mL	4.0 mL	M	M	0.174
III	5.0 mL	2.0 mL	3.0 mL	M	M	0.370
IV	5.0 mL	3.0 mL	2.0 mL	M	M	0.512
V	5.0 mL	4.0 mL	1.0 mL	M	M	0.696
VI	5.0 mL	5.0 mL	0.0 mL	M	M	0.836

 

ICE Charts

Test Solution Keq = 260	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 280	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 260	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 290	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 280	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

CONCLUSION AND EVALUATION:

1. Comment on your Keq values.  Do your results convince you that Keq is a constant value regardless of the initial concentrations of the reactants?  Why or why not?The results of our Keq values convinced me that Keq is not a constant value. Our values jumped around between 260 and 290, leading us to the conclusion that Keq is not a constant value and will change if you alter any of the initial concentrations.
2. Calculate the average value of Keq from your five trials.  The actual value of Keq  for this reaction at 25oC is reported as 280.  Calculate (should you use all of your values?) the percent difference of your average value from the reported value:
   Actual Value: 280
   Experimental Value: 273.91
   % difference: (273.91 – 280) / 280 = 2.17%