Laboratory6 Spectroscopic Determination of an Equilibrium Constant DATE: NAME SE
ID: 712532 • Letter: L
Question
Laboratory6 Spectroscopic Determination of an Equilibrium Constant DATE: NAME SECTION: INSTRUCTOR In-Lab Guidelines (This is a guide to the information that you should be observing while in the laboratory. Record this information in the Laboratory Notebook. Turn in the duplicat period.) e pages of your observations to your Instructor before you leave the laboratory 2S Laboratory Temperature Concentration of Stock Fe(NO,), soln 0020 Concentration of stock KSCN soln. Trhal eKSCVHO Total Vol Fe(NO)KSCN H,o mL %T Observations: (anything you observed that may have affected your experiment, formation of a precipitate, spils, etc.) LABORATORY SPECTROSCOPIC RETERMDLExplanation / Answer
Using = 4400 L/mol-cm
Path length, b = 1 cm
C = A / ( b)
A = 2 – log(%T)
We get below table:
Trial
% Transmittance
Absorption
[FeSCN]
1
7.2
1.14
0.00026
2
10.4
0.98
0.000223
3
16
0.80
0.000181
4
25.6
0.59
0.000134
Initial concentrations are obtained by using, M1 * V1 = M2 * V2
Trial
Total volume
Fe(NO3)3 volume, mL
KSCN volume, mL
Initial [Fe3+], M
Initial [SCN-], M
1
10
5
5
0.001
0.001
2
10
5
4
0.001
0.0008
3
10
5
3
0.001
0.0006
4
10
5
2
0.001
0.0004
Equilibrium concentrations:
[Fe3+]eq = [Fe3+]0 – [FeSCN]eq
[SCN-]eq = [SCN-]0 – [FeSCN]eq
Keq = [FeSCN]eq / ([Fe3+]eq [SCN-]eq)
Trial
Initial [Fe3+]
Initial [SCN-]
Eq. [FeSCN]
Eq. [Fe3+]
Eq. [SCN-]
Keq
Average Keq
1
0.001
0.001
0.00026
0.00074
0.00074
473.9
521.2
2
0.001
0.0008
0.000223
0.00078
0.00058
498.9
3
0.001
0.0006
0.000181
0.00082
0.00042
526.9
4
0.001
0.0004
0.000134
0.00087
0.00027
585.3
Possible errors in experiment:
a) Inaccurate preparation of initial solutions.
b) Improper readings given by instruments.
c) Temperature variations of the solution.
Trial
% Transmittance
Absorption
[FeSCN]
1
7.2
1.14
0.00026
2
10.4
0.98
0.000223
3
16
0.80
0.000181
4
25.6
0.59
0.000134
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