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Use of spectrophotometry to determine Ka

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This involves the use of the equation;

pH = pKa + log (activity coefficent of anion) + log (D -Dha)/(Da- - D),

from the equation it is neccesary to plot pH against log(D - Dha)/(Da- -D).

This appears to be the straight line eqn which can be solved (y = mx + c) for the function pKa + log (activity coefficient of anion).

Is this approach correct or can you give an example of how to solve?

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Solution Summary

The expert uses spectrophotometry to determine the Ka. The straight line equations are determined.

See Also This Related BrainMass Solution

Bromothymol Blue : Ka and Ionic Strength


1. Explain why it is not necessary to know the exact concentration of bromothymol blue in the solution.

2. The pKa value can also be determined from Figure 4 - explain.

3. The acid dissociation constant for bromothymol blue is dependent on ionic strength of solution.

Determine the ionic strength of bromothymol blue by interpolating the values given below.

Please see the attached file for the fully formatted problems.

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