Phenobarbitol Drug Development - 11a. Spectrophotometric pKa Determination

11. Spectrophotometric Determination of pK_a of Bromothymol Blue - Table of Values

Lab Guide:

This is the sequence of steps in this laboratory determination:

Prepare buffer phosphate solutions with varying pH.
Use an indicator (bromothymol blue) as the weak acid whose pK_a we will determine.
read the pH of EACH sample.
read samples at the wavelengths to determine amount of ionized.
read samples at wavelength to determine amount of unionized.
graph data to determine where the concentrations are equal.

1.	0.1% bromo-thymol blue (ml)	0.1M KH₂PO₄ (ml)	0.1M Na₂HPO₄ (ml)	H₂0(ml)	pH	450 %t	450 A	550 %t	550 A
2.	1.0	5.0	0.0	19.0
3.	1.0	5.0	1.0	18.0
4.	1.0	10.0	5.0	9.0
5.	1.0	5.0	10.0	9.0
6.	1.0	1.0	5.0	18.0
7.	1.0	1.0	10.0	13.0
8.	1.0	0.0	5.0	19.0

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