The determination of the pK values of some substituted aliphatic carboxylic acids at 10, 25, and 40°
The pK values of valeric, 2,2-dimethylpropionic, 2-methylvaleric, 3-methylvaleric, 2,2-dimethylvaleric, heptanoic, and octanoic acids at 10, 25, and 40° were determined from pH titration data. All the measurements were made in an aqueous solution. It was assumed that the γ values were the same for all species of the same charge type and that the activity coefficients for neutral species were unity. A Debye-Hückel equation was used to correct the concentration quotient to the corresponding thermodynamic constant. The pK values as a function of temperature fall in two different groups as predicted by King: (1) the pK values show a minimum at room temperature; (2) the pK values show a minimum near O° and increase as the temperature rises. The length of the carbon chain of an unsubstituted aliphatic carboxylic acid has little effect on the pK values; however, the methyl group attached on the C-2 position has the effect of increasing the pK value of the carboxylic acid. This is shown by the experimental results and a suggested explanation is given. The calculation of the pK values was carried out using an IBM 360 computer.
College and Department
Chemistry and Biochemistry
BYU ScholarsArchive Citation
Tsang, Jii-Hang, "The determination of the pK values of some substituted aliphatic carboxylic acids at 10, 25, and 40°" (1969). Theses and Dissertations. 8370.