Equilibrium

Standard solutions



Pg. 28 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

Standard solutions



Pg. 28 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

Experimental test solutions





Pg. 30 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

Calibration Curve



0.8

y = 4697.5x + 0.0008 1.600E-04

0.7

1.40E-04

0.6 1.16E-04

absorbance









1.200E-04

0.5

8.81E-05

0.4 8.00E-05

0.3 5.92E-05 Standards

0.2 4.00E-05 Experimentals

2.96E-05

0.1

0 0.00E+00

0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E

[Fe(SCN)2+], M

Experimental test solutions



Pg. 30 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



units are M 1 2 3 4 5

[Fe(SCN)2+]equil

2.96 x 10-5

(graph)

[Fe3+]initial



[SCN-]initial



[Fe3+]equil



[SCN-]equil



K



Average K

Initial Concentrations for Trial 1



(0.00200 M Fe3 ) (2.50 mL)

initial [Fe3 ]   1.00 x 103 M Fe3

5.00 mL

Experimental test solutions



units are M 1 2 3 4 5

[Fe(SCN)2+]equil

2.96 x 10-5

(graph)

[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

2.96 x 10-5

(graph)

[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

Initial Concentrations for Trial 1



(0.00200 M SCN ) (0.50 mL)

initial [SCN ]   2.00 x 104 M SCN

5.00 mL

Experimental test solutions



units are M 1 2 3 4 5

[Fe(SCN)2+]equil

2.96 x 10-5

(graph)

[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

[ ], 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



[Fe3+]equil = 1.00 x 10-3 M – 2.96 x 10-5 M = 9.70 x 10-4 M









[SCN-]equil = [SCN-]-initial – [Fe(SCN)2+]equil



[SCN-]equil = 2.00 x 10-4 M – 2.96 x 10-5 M = 1.70 x 10-4 M

Experimental test solutions



units are M 1 2 3 4 5

[Fe(SCN)2+]equil

2.96 x 10-5

(graph)

[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

2.96 x 10-5

(graph)

[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

Determine the numerical value of the equilibrium constant, K





[Fe(SCN)2 ]equil

K  3 

[Fe ]equil [SCN ]equil



5

(2.96 x 10 M)

K  4 4 = 179

(9.70 x 10 M) (1.70 x 10 M)

Experimental test solutions



units are M 1 2 3 4 5

[Fe(SCN)2+]equil

2.96 x 10-5

(graph)

[Fe3+]initial 1.0 x 10-3 1.0 x 10-3 1.0 x 10-3 1.0 x 10-3 1.0 x 10-3



[SCN-]initial 2.0 x 10-4



[Fe3+]equil 9.7 x 10-4



[SCN-]equil 1.7 x 10-4



K 180



Average K