A Simplified Method for Finding the pKa of an Acid-Base Indicator by Spectrophotometry

Journal of Chemical Education

Volumn 76, Issue 3, 1999, Pages 395-398

  Patterson, George S ^a  

^a SUFFOLK UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000706588     PISSN: 00219584     EISSN: None     Source Type: Journal    
DOI: 10.1021/ed076p395     Document Type: Article

References (16)

1. Brown, W. E.; Campbell, J. A. J. Chem. Educ. 1968, 45, 674-675. Several indicators were studied by the methods of Ramette (4) and Tobey (7).
2. HIn values. (Note that this is the correct equation. The equation given in ref 2 is incorrect.) Data are presented for thymol blue.
3. a value for each buffered solution using concentration and absorbance data and activity coefficients, then averages the values.
4. a.
5. a of bromophenol blue from eq 1 using absorbancies from the Beer's law data and the absorbances of the pH 3.4-4.6 solutions or from a plot of eq 3, similar to the method described here.
6. a is the y-intercept of the graph.
7. a values for each solution. The values were averaged.
8. a. This equation can be derived from eq 3.
9. a by both methods described by Sawyer et al. (6).
10. Ramette, R. W. Chemical Equilibrium and Analysis; Addison-Wesley: Reading, MA, 1981; Chapter 13.
11. Ramette, R. W. J. Chem. Educ. 1967, 44, 647-654.
12. Lange's Handbook of Chemistry; Dean, J. A., Ed.; McGraw-Hill: New York, 1992; pp 8.115-8.116.
13. Handbook of Analytical Chemistry; Meites, L., Ed.; McGraw-Hill: New York, 1963; Sec. 3 p 36.
14. Skoog, D. A.; West, D. M. Analytical Chemistry: An Introduction, 4th ed.; Saunders: Philadelphia, 1986; p 164.
15. Kolthoff, I. M. Acid-Base Indicators; Rosenblum, C., Translator; Macmillan: New York, 1937; pp 112 and 221-224.
16. Ramette, R. W.; Dratz, E. A.; Kelly, P. W. J. Phys. Chem. 1962, 66, 527-532.