The value of K c for a reaction is dependent on concentration of reactants in wh
ID: 893460 • Letter: T
Question
The value of Kc for a reaction is dependent on concentration of reactants in what way?
Higher concentrations of reactants will give a larger Kc.
Higher concentrations of reactants will give a lower Kc.
Concentrations effects will vary between reactions and the specific equilibrium expression must be known.
Concentration does not affect the equilibrium constant for a reaction.
3 points
QUESTION 2
Using the equilibrium reaction that you are using in your experiment, a student measures out initial concentrations of 0.00168 M Fe3+and 0.00411 M SCN-. If the equilibrium value of Fe(SCN)2+ is found to be 0.00046 M, what is the equilibrium concentrations of Fe3+. Give all anwers to prelab questions in standard (not scientific) notation.
3 points
QUESTION 3
Absorbance of light by a solution is directly proportional to which of the following (choose all that apply)?
Concentration of absorbing species
The path length that the light passes through the solution
The molar absorptivity coefficient
None of the above
QUESTION 4
When analyzing your calibration curve, the slope of the line will be equivalent to ...
the concentration of the solution.
the pathlength of the solution.
the molar absorptivity of the solution.
the product of path length and molar absorptivity.
QUESTION 5
From a plot of your calibration data, the slope is found to be 33.3. What will be the concentration of your absorbing species in a solution that has an absorbance of 0.113?
QUESTION 6
Using the equilibrium reaction that you are using in your experiment, a student measures out initial concentrations of 0.00166 M Fe3+and 0.00499 M SCN-. If the equilibrium value of Fe(SCN)2+ is found to be 0.00048 M, what is the value of Kc. Give all anwers to prelab questions in standard (not scientific) notation.
Higher concentrations of reactants will give a larger Kc.
Higher concentrations of reactants will give a lower Kc.
Concentrations effects will vary between reactions and the specific equilibrium expression must be known.
Concentration does not affect the equilibrium constant for a reaction.
Explanation / Answer
a) the equilibrium constant of a reaction depends only on the temperature and independant on concentration or pressure.
b) The equilibrium reaction will be
Fe3+ + SCN- ---> Fe(SCN)2+
Initial 0.00168 0.00411 0
Change -x -x +x
Equilibrium 0.00168-x 0.00411-x x
Given that
x =0.00046 M (equilbrium concentration of Fe(SCN)+2
hence
[Fe3+] = 0.00168-0.00046 = 0.00122 M
3) Absorbance of light by a solution is directly proportional to concentration and path length both [Concentration of absorbing species and The path length that the light passes through the solution] as per Beer Lambert's law
4) As per Beer Lambert's law
A = e.c.l
where
e= absroptivity
c= concentration
l = length
So if we are plotting graph between absrobance and concentration the slope will be the product of path length and molar absorptivity.
Generally we consider the path length to be unity so it could be only The molar absorptivity coefficient
5)A= e.c.l
slope = 33.3
A = 0.113
concentration = A / slope = 0.113 / 33.3 = 0.0034 M
5) The equilibrium reaction will be
Fe3+ + SCN- ---> Fe(SCN)2+
Initial 0.00166 0.00499 0
Change -x -x +x
Equilibrium 0.00166-x 0.00499-x x
Given that
x =0.00048 M (equilbrium concentration of Fe(SCN)+2
hence
[Fe3+] = 0.00166-0.00048 = 0.00118 M
[SCN-]= 0.00499-0.00048 = 0.00451
Kc = [Fe(SCN)+2] / [ Fe+3][SCN-] = 0.00048 / 0.00118 X 0.00451 = 90.195
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