Chemistry Lab 12 2x6954

Experiment 12 Period 4

Austin Grant Miranda Began January 5, 2012 AP Chemistry The Determination of Keq for FeSCN2+

OBJECTIVE: 1. To determination of Keq for FeSCN2+ PROCEDURE: See laboratory worksheet “The Determination of Keq for FeSCN2+” attached. EXPERIMENTAL DATA: Reference Solution Temperature

20.25°C [FeSCN2+]

Sample

Absorbance -5

Reference Solution #1

4.0 x 10 M

0.150

Reference Solution #2

6.0 x 10-5 M

0.184

Reference Solution #3

8.0 x 10-5 M

0.316

Reference Solution #4

1.0 x 10-4 M

0.365

Reference Solution #5

1.2 x 10-4 M

0.454

Test Solution Temperature Sample Reference Solution #1

20.25°C [FeSCN2+]

[SCN-] -3

1.0 x 10 M -3

Absorbance -4

0.112

-4

2.0 x 10 M

Reference Solution #2

1.0 x 10 M

4.0 x 10 M

0.182

Reference Solution #3

1.0 x 10-3 M

6.0 x 10-4 M

0.264

Reference Solution #4

1.0 x 10-3 M

8.0 x 10-4 M

0.357

Reference Solution #5

1.0 x 10-3 M

1.0 x 10-3 M

0.407

Results Solution Sample

[FeSCN2+]eq

Reference Solution #6

3.37 x 10-5 M

9.66 x 10-4 M 1.66 x 10-4 M

210

Reference Solution #7

5.15 x 10-5 M

9.48 x 10-4 M 3.49 x 10-4 M

155

-5

Reference Solution #8

7.22 x 10 M -5

[SCN-]eq

[Fe3+]eq

Keq

-4

147

-4

9.28 x 10 M 5.28 x 10-4 M

Reference Solution #9

9.58 x 10 M

9.04 x 10 M 7.04 x 10-4 M

150

Reference Solution #10

1.08 x 10-4 M

8.82 x 10-4 M 8.92 x 10-4 M

137

Average Value

160

Average deviation

20

Calculations: Calculating Resultant Concentration of [FeSCN2+] using slope formula and absorbance Y = 3945X – 0.021 Test Solution #6 Absorbance = 0.112 X = 3.37 x 10-5 M FeSCN2+

0.112 = 3945X – 0.21

Calculating Resultant Concentration of [Fe3+] and [SCN-] using ICE [Fe3+]eq I C E

+

1.0 x 10-3 M -3.37 x 10-5 M 9.66 x 10-4 M

SCN1-eq 2.0 x 10-4 M -3.37 x 10-5 M 1.66 x 10-4 M

↔

FeSCN2+ 0 0 3.37 x 10-5 M

Calculating K for the Test K K K

= = =

[FeSCN2+] / [Fe3+] x [SCN1-] [3.37 x 10-5 M FeSCN2+] / [9.66 x 10-4 M Fe3+] x [1.66 x 10-4 M SCN1-] 210.2 = 210 M-1S-1

Graph: Equation Determined by Calculator Y = 3945X – 0.021 Calibration Curve for Absorbance of FeSCN2+

Absorbance at 450 nm

0.500 0.400 0.300

Absorbance Linear regression for Absorbance

0.200 0.100 0.000 2.00 4.00

6.00

8.00 10.00 12.00 14.00

Molar Concentration of FeSCN2+ (x 10-5)