Data Sheet 2 Preparing and Analyeing the Mixtures o \'M HNO, solution, mol L of

Question

Data Sheet 2 Preparing and Analyeing the Mixtures o 'M HNO, solution, mol L of RekNOsh in 10 of NascN in 10 to- M HNo, soluti an, mol L solution eemperature, c 10 x added, mL volume of NascN in x 10 'M HNO's solution L L initial Fe' ion concentration, mol L-1 initial SCN ion concentration, mol L percent transmittance. laboratory instructor approval of data final equilibrium FeNCs ion concentration, final equilibrium Fe ion concentration, mol L final equilibrium SCN ion concentration, equilibrium constant expression equilibrium constant,

Explanation / Answer

From the given set of data

1. (1) initial [SCN-] = [FeNCS]2+

For E2,

[SCN-] = [FeNCS]2+ = 0.002 M x 1 ml/10 ml

                                  = 0.0002 M

Similarly the calculation can be done for other samples

(2) slope of Beer's plot is molar absorptivity

slope = (0.443 - 0.22)/(0.0002)

              = 1115 M-1.cm-1

(3) Equilibrium concentrations can be calculated by,

Prepare another set of solutions

Find absorbance for each solution

Calculate [FeNCS]2+eq = absorbance/molar absorptivity

Calculate [Fe3+]eq = [Fe3+] initial - [FeNCS]2+eq

and,

[SCN-]eq = [SCN-] initial - [FeNCS]2+eq

(4) From the above data caluclate Keq

Keq = [FeNCS]2+eq/[Fe3+]eq.[SCN-]eq

2.(1) Fingerprints on the cuvette does not allow the light to be transmitted from the sample. Thus the %T would be lower. since,

absorbance = 2 - log(%T)

absorbance for the samples would appear higher than actual value

(2) The calculated [FeNCS]2+ would thus be higher than the actual value, as more complex absorbs more light and transmits less.

(3) The calculated Keq would thus be higher as [FeNCS]2+ is in numerator.

3. concentration of [SCN-] is much lower than [Fe3+] and thus when all of [SCN-] has reacted and formed complex, reaction stops. Thus it is safe to assume, [SCN-] has converted into complex upon reaction with excess [Fe3+] in solution.

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