Assuming the buffer is composed of equal concentrations of a weak acid and its conjugate base, the pH of the buffer will be around 9.00. To calculate the mass of HCl that can be neutralized before the pH drops below 9.00, we need to use the Henderson-Hasselbalch equation and the acid dissociation constant (Ka) of the weak acid. With this information, we can determine the buffer capacity and the maximum amount of HCl that can be neutralized without significant changes in pH.