Hi, I\'m not sure how to do this question based on labratory data. Any help is a

Question

Hi, I'm not sure how to do this question based on labratory data. Any help is appreciated thanks!

1. Looking at Table 5 (data sheet), how is Kc related to the initial concentrations ( [Fe3+]o and [SCN–]o)? Is it what you expected? (Explain briefly)

Table 5 - Equilibrium constant, at room temperature Tube # Absorbance             Initial concentrations Concentrations at equilibrium Kc* [Fe3+]o [SCN-]0 [FeSCN2+]eq [Fe3+]eq [SCN-]eq (au) (M) (M) (M) (M) (M) (M-1) 5 0.622 0.180 0.00019 0.00016 1 0.303 0.001 0.00038 0.00015 0.00085 0.00023 767.3 2 0.456 0.001 0.00057 0.00035 0.00065 0.00022 2447.6 3 0.581 0.001 0.00076 0.00059 0.00041 0.00017 8464.8 4 0.686 0.001 0.00095 0.00089 0.00011 0.00060 13,484.8 Average 6291.1 *temperature 19.8 degree C Total volume tube #5 10.1 mL

Explanation / Answer

Write down the reaction taking place (and the ICE CHART) as

Fe3+ (aq)          +          SCN- (aq) -------->       [Fe(SCN)]2+ (aq)

Initial                      [Fe3+]0                     [SCN-]0                                0

Change             -[Fe(SCN)2+]              –[Fe(SCN)2+]                  [Fe(SCN)2+]

Equilibrium ([Fe3+]0 – [Fe(SCN)2+] ([SCN]0 – [Fe(SCN)2+]     [Fe(SCN)2+]

The equilibrium constant is given by

Kc = [Fe(SCN)2+]eq/[Fe3+]eq[SCN-]eq = [Fe(SCN)2+]eq/([Fe3+]0 – [Fe(SCN)2+]eq)([SCN-]0 – [Fe(SCN)2+]0)

Fill up the table as given:

Tube

Absorbance

Initial concentrations

Concentrations at equilibrium

Kc

[Fe3+]0 (M)

[SCN-]0 (M)

[Fe(SCN)2+] (M)

[Fe3+]eq (M)

[SCN-] (M)

1

0.303

0.001

0.00038

0.00015

0.00085

0.00023

767.3

2

0.456

0.001

0.00057

0.00035

0.00065

0.00022

2447.5

3

0.581

0.001

0.00076

0.00059

0.00041

0.00017

8464.8

4

0.686

0.001

0.00095

0.00089

0.00011

0.00006

134848.5

5

0.622

0.180

0.00019

0.00016

0.17984

0.00003

29.6

Tube

Absorbance

Initial concentrations

Concentrations at equilibrium

Kc

[Fe3+]0 (M)

[SCN-]0 (M)

[Fe(SCN)2+] (M)

[Fe3+]eq (M)

[SCN-] (M)

1

0.303

0.001

0.00038

0.00015

0.00085

0.00023

767.3

2

0.456

0.001

0.00057

0.00035

0.00065

0.00022

2447.5

3

0.581

0.001

0.00076

0.00059

0.00041

0.00017

8464.8

4

0.686

0.001

0.00095

0.00089

0.00011

0.00006

134848.5

5

0.622

0.180

0.00019

0.00016

0.17984

0.00003

29.6

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