Concept explainers
The equilibrium constant for the conjugate acid-base pair
(a) calculate the absorbance at 430 nmand 600 nm for the following indicator concentrations:
3.00 × 10-4M,2.00 × 10-4M, 1.00 × 10-4M, 0.500 × 10-4 M, and 0.250 × 10-4M.
(b) plot absorbance as a function of indicator concentration.
(a)
Interpretation:
Absorbance values of the conjugate acid-base pair solutions of different concentrations at
Concept introduction:
The absorbance can be calculated using the following formula:
For the given conjugate acid-base pair, equilibrium can be written as,
Answer to Problem 13.11QAP
Explanation of Solution
Let’s use the equilibrium equation to find the concentrations of HIn and In-(denoted as [HIn] and [In-]) at a situation in which the total concentration (cHIn) is
Now, the absorbance values of this solution at 430 and 600 nm can be calculated as follows,
The cell length (b) is not given in the question, therefore taken as 1.00cm.
Similarly, other absorbance values can be calculated for solutions with different concentrations.
(b)
Interpretation:
Absorbance as a function of indicator concentration should be plotted.
Explanation of Solution
The data obtained is as follows:
From the data, the graph between absorbance and concentration can be plotted as follows:
Here, blue curve indicates the plot at 430 nm and orange curve indicates the same at 600 nm.
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Chapter 13 Solutions
Principles of Instrumental Analysis
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