DETERMINATION OF THE Kc FOR FeSCN2+
DATA:
Absorbance of Standard Solution:
Solution #
Absorbance
Temperature
1
2
3
4
5
CALCULATIONS:
Calculate the initial concentration of SCN- in the Standard solution based on dilution with the ferric ion solution. (For "initial" concentration, assume no reaction has occurred yet. After reaction in the Standard Solution, the equilibrium concentration of FeSCN2+ is considered to be equal to the initial concentration of SCN-)
Respond to Items 2-5 below to complete the data table. Show a sample calculation for each Item. ("ini" refers to after mixing but before reaction)
Table
1
2
3
4
5
[Fe3+]ini, M
[SCN-]ini, M
Absorbance
[FeSCN2+]eq, M
[Fe3+]eq, M
[SCN-]eq, M
Kc
For the equilibrium samples 1-5, calculate the initial concentrations of Fe3+(aq) and SCN-(aq) based on their original concentrations and the dilution involved in preparing the solutions.
From the measured absorbance for each equilibrium sample, calculate the equilibrium concentration of FeSCN2+.
From the concentration of FeSCN2+ at equilibrium and the initial concentration of Fe3+ and SCN-, calculate the equilibrium concentrations of Fe3+ and SCN- for the equilibrium solutions.
Calculate Kc for each equilibrium solution.
Data:
Straight stock Absorbance: 0.795
Trial 1 absorbance: 0.540
Trial 2 absorbance: 0.720
Trial 3 absorbance: 0.8802
Trial 4 absorbance: 0.947
Trial 5 absorbance: 2.40
Table 1: Solution Composition for Iron-Thiocyanate Solutions
Standard Equilibrium Solutions
1
2
3
4
5
Volume 0.200 M Fe3+, mL
18.0
____
____
____
____
____
Volume 0.0020 M Fe3+, mL
____
5.0
5.0
5.0
5.0
5.0
Volume 0.0020 M SCN-, mL
2.0
1.0
2.0
3.0
4.0
5.0
Volume water, mL
____
4.0
3.0
2.0
1.0
0.0
[Fe3+]ini, M (Calculated)
____
[SCN-]ini, M (Calculated)
Absorbance
[FeSCN2+]eq, M
[Fe3+]eq, M (Calculated)
____
[SCN-]eq, M (Calculated)
~ 0
Kc