The pH is approximately 9.50, and the pOH is approximately 4.50 for the given boric acid (H3BO3) and sodium borate (Na2B4O7) solution; pKa for B(OH)3 is 9.24.
To determine the pH and pOH of the solution, which contains boric acid (H3BO3) and sodium borate (Na2B4O7), one needs to consider the ionization of boric acid in water. Boric acid acts as a weak acid and undergoes partial ionization in aqueous solution:
⇌
The equilibrium constant for this ionization is represented by the acidity constant (Ka). In this case, the pKa for boric acid is given as 9.24.
Since boric acid is a weak acid, an ICE (Initial, Change, Equilibrium) table is employed to determine the equilibrium concentrations of each species.
After calculating the concentrations, the pH and pOH can be determined. The pH is found using the expression pH=−log[H+ ], and the pOH is found using pOH=−log[OH-]. The relation between pH and pOH is pH+pOH=14 in water at 25°C.
In this case, the calculated pH is approximately 9.50, and the pOH is approximately 4.50, reflecting the basic nature of the solution due to the presence of the weak base
.