Final answer:
To calculate the exact pH of a 0.0100 M sodium benzoate solution, the pKa of benzoic acid is required along with the equilibrium concentrations post-hydrolysis. An estimation can be made that the solution will be basic, with a pH above 7.
Step-by-step explanation:
In order to calculate the pH of a sodium benzoate solution, you need to know the pKa of benzoic acid. The pKa of benzoic acid is given to be 4.2. Sodium benzoate is the conjugate base of benzoic acid, so it acts as a weak base in solution. To calculate the pH, you need to consider the concentration of sodium benzoate and use the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). In this case, [A-] refers to the concentration of sodium benzoate and [HA] refers to the concentration of benzoic acid.
To calculate the pH of a 0.0100 M sodium benzoate solution, we must recognize that sodium benzoate is a salt formed from the weak acid benzoic acid and a strong base NaOH. Since benzoic acid is a weak acid, sodium benzoate will hydrolyze in water, generating benzoate ions (C6H5COO-) and hydroxide ions (OH-). The benzoate ions then react with water to form benzoic acid and hydroxide ions, slightly increasing the pH of the solution. However, without the pKa of benzoic acid and the concentration of benzoic acid formed after hydrolysis, a direct calculation is not possible. An approximation can still be made by assuming that the contribution of hydroxide ions to the pH will only have a minor impact, thus sodium benzoate being a salt from a weak acid and strong base will result in a basic solution and therefore, the pH is expected to be above 7.