Concept explainers
The equilibrium constant for the reaction
Four solutions were preparedby dissolving 4.00 × 10-4, 3.00 × 10-4, 2.00 × 10-4,and 1.00 × 10-4 moles of K2 Cr2 O7 in water and diluting to 1.00 L with a pH 5.60 buffer. Derive theoretical absorbance values (1.00-cm cells) for each solution and plot the data for (a) 345 nm, (b) 370 nm, and (c) 400 nm.
(a)
Interpretation:
The theoretical absorbance value for 345 nm should be derived and the data should be plotted.
Concept introduction:
The relationship between absorbance and concentration of absorbance is linear. If the incident light
In the case of no absorbing sample, all the light gets passed and the value of
Explanation of Solution
Given:
The equilibrium constant is
The given reaction is
The equilibrium constant for the given reaction is
The formula to determine pH is:
Therefore
For the given reaction the expression for the equilibrium constant can be written as
The equilibrium concentration of dichromate is
The theoretical absorbance value of the first solution can be calculated as below
For the second solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the third solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the fourth solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below:
Now take the values in excel and plot to get the graph:
(b)
Interpretation:
The theoretical absorbance value for 370 nm should be derived and the data should be plotted.
Concept introduction:
The relationship between absorbance and concentration of absorbance is linear. If the incident light
In the case of no absorbing sample, all the light gets passed and the value of
Explanation of Solution
Given:
The equilibrium constant is
The given reaction is
The equilibrium constant for the given reaction is
The formula to determine pH is:
Therefore
For the given reaction the expression for the equilibrium constant can be written as
The equilibrium concentration of dichromate is
The theoretical absorbance value of the first solution can be calculated as below
For the second solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the third solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the fourth solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
Now take the values in excel and plot to get the graph:
(c)
Interpretation:
The theoretical absorbance value for 400 nm should be derived and the data should be plotted.
Concept introduction:
The relationship between absorbance and concentration of absorbance is linear. If the incident light
In the case of no absorbing sample, all the light gets passed and the value of
Explanation of Solution
Given:
The equilibrium constant is
The given reaction is
The equilibrium constant for the given reaction is
The formula to determine pH is:
Therefore
For the given reaction the expression for the equilibrium constant can be written as
The equilibrium concentration of dichromate is
The theoretical absorbance value of the first solution can be calculated as below
For the second solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the third solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
The theoretical absorbance value of the first solution can be calculated as below
For the fourth solution, everything will remain the same, just the equilibrium concentration of dichromate will change to
So, the new required concentration will be as
Theoretical absorbance value of first solution can be calculated as below
Now take the values in excel and plot to get the graph:
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Chapter 13 Solutions
Principles of Instrumental Analysis
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