Fe3+ (aq) + SCN- (aq)Fe(SCN)2+
(aq)colorless colorless
]SCN[ ][Fe
][Fe(SCN)K
equilequil3
equil2
Fe3+ (aq) + SCN- (aq)Fe(SCN)2+
(aq)colorless colorless reddish-orange
A (blank) B C D E
volume of 0.200 M Fe3+ 10.0 mL 10.0 mL 10.0 mL 10.0 mL 10.0 mL
volume of 0.00200 M SCN- 0.00 mL 0.50 mL 1.00 mL 1.50 mL 2.00 mL
0.200 M HNO3 dilute to 25.00 mL mark
equilibrium [Fe(SCN)2+], M 0.00 4.00 x 10-5 8.00 x 10-5 12.0 x 10-5 16.0 x 10-5
Standard Solutions for calibration curve Pg. 32
Standards [Fe(SCN)2+], M absorbance
standard A 0.00
standard B 4.00 x 10-5
standard C 8.00 x 10-5
standard D 12.0 x 10-5
standard E 16.0 x 10-5
Pg. 36
Standard solutions
Standard solutions
Standards [Fe(SCN)2+], M absorbance
standard A 0.00 0.000
standard B 4.00 x 10-5 0.196
standard C 8.00 x 10-5 0.371
standard D 12.0 x 10-5 0.557
standard E 16.0 x 10-5 0.759
Pg. 36
Experimental test solutions
Experimental absorbance [Fe(SCN)2+], M
solution 1
solution 2
solution 3
solution 4
solution 5
Pg. 36
Blank 1 2 3 4 5
mL 0.00200 M SCN- 0.00 0.50 1.00 1.50 2.00 2.50
mL 0.00200 M Fe3+ 2.50 2.50 2.50 2.50 2.50 2.50
mL 0.200 M HNO3 2.50 2.00 1.50 1.00 0.50 0.00
Experimental Solutions Pg. 34
Experimental test solutions
Experimental absorbance [Fe(SCN)2+], M
solution 1 0.139
solution 2 0.278
solution 3 0.414
solution 4 0.546
solution 5 0.658
Pg. 36
Standard solutions
Standards [Fe(SCN)2+], M absorbance
standard A 0.00 0.000
standard B 4.00 x 10-5 0.196
standard C 8.00 x 10-5 0.371
standard D 12.0 x 10-5 0.557
standard E 16.0 x 10-5 0.759
Pg. 36
Calibration Curve
0.00E+00
4.00E-05
8.00E-05
1.200E-04
1.600E-04
2.96E-05
5.92E-05
1.40E-041.16E-04
8.81E-05
y = 4697.5x + 0.0008
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E-04
[Fe(SCN)2+], M
abs
orb
an
ce
Standards
Experimentals
Experimental absorbance [Fe(SCN)2+], M
solution 1 0.139 2.96 x 10-5
solution 2 0.278 from graph
solution 3 0.414 from graph
solution 4 0.546 from graph
solution 5 0.658 from graph
Experimental test solutions
Pg. 36
Calibration Curve
0.00E+00
4.00E-05
8.00E-05
1.200E-04
1.600E-04
2.96E-05
5.92E-05
1.40E-041.16E-04
8.81E-05
y = 4697.5x + 0.0008
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E-04
[Fe(SCN)2+], M
abs
orb
an
ce
Standards
Experimentals
Experimental absorbance [Fe(SCN)2+], M
solution 1 0.139 2.96 x 10-5
solution 2 0.278 5.92 x 10-5
solution 3 0.414 from graph
solution 4 0.546 from graph
solution 5 0.658 from graph
Experimental test solutions
Pg. 36
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial
[SCN-]initial
[Fe3+]equil
[SCN-]equil
K
Average K
Experimental test solutions
Initial Concentrations for Trial 1
mL00.5
)mL50.2()FeM00200.0(]Fe[ initial
33
33 Fe M 10 x 1.00
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3
[SCN-]initial
[Fe3+]equil
[SCN-]equil
K
Average K
Experimental test solutions
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3
[SCN-]initial
[Fe3+]equil
[SCN-]equil
K
Average K
Experimental test solutions
Initial Concentrations for Trial 1
mL00.5
)mL50.0()SCNM00200.0(]SCN[ initial
SCN M 10 x 2.00 4
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3
[SCN-]initial 2.00 x 10-4
[Fe3+]equil
[SCN-]equil
K
Average K
Experimental test solutions
[ ], M Fe3+ (aq) + SCN- (aq) Fe(SCN)2+ (aq)
initial 1.00 x 10-3 2.00 x 10-4 0
change x x +x
equilibrium 1.00 x 10-3 x 2.00 x 10-4 x x
x = [Fe(SCN)2+]equil (obtained from graph)
Equilibrium Concentrations for Trial 1
[Fe3+]equil = [Fe3+] initial – [Fe(SCN)2+]equil
[SCN-]equil = [SCN-] initial – [Fe(SCN)2+]equil
[Fe3+]equil = 1.00 x 10-3 M – 2.96 x 10-5 M = 9.70 x 10-4 M
[SCN-]equil = 2.00 x 10-4 M – 2.96 x 10-5 M = 1.70 x 10-4 M
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3
[SCN-]initial 2.00 x 10-4
[Fe3+]equil 9.70 x 10-4
[SCN-]equil
K
Average K
Experimental test solutions
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3
[SCN-]initial 2.00 x 10-4
[Fe3+]equil 9.70 x 10-4
[SCN-]equil 1.70 x 10-4
K
Average K
Experimental test solutions
]SCN[ ][Fe
][Fe(SCN)K
equilequil3
equil2
Determine the numerical value of the equilibrium constant, K
M) 10 x 70.1( M) 10 x 70.9(
M) 10 x 96.2( K
44
5
= 179
units are M 1 2 3 4 5
[Fe(SCN)2+]equil (graph)
2.96 x 10-5
[Fe3+]initial 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3 1.00 x 10-3
[SCN-]initial 2.00 x 10-4
[Fe3+]equil 9.70 x 10-4
[SCN-]equil 1.70 x 10-4
K 179
Average K
Experimental test solutions
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