Ka (acid dissociation constant) is a measure of the strength of an acid in a solution. In the case of phosphate buffered saline, it refers to the equilibrium constant for the dissociation of phosphate ions in the solution.
The values 6.2E-8 or 1.59E-7 represent the Ka values for phosphate buffered saline at different temperatures. They are both very small numbers, indicating that the solution is weakly acidic.
Ka for phosphate buffered saline can be determined experimentally by measuring the concentration of hydrogen ions (H+) and phosphate ions (HPO42-) in the solution and using the equilibrium equation to calculate the Ka value.
Ka is an important parameter for understanding the behavior of phosphate buffered saline in solution. It can help determine the pH of the solution and how it will interact with other substances, such as proteins or cells.
The Ka value for phosphate buffered saline may change with temperature, as shown by the two different values given. This is because temperature can affect the strength of the acid, as well as the dissociation of phosphate ions in the solution.