What mass of sodium benzoate should you add to 150.0 mL of a 0.15 M benzoic acid solution to obtain a buffer with a pH of 4.25? (Assume no volume change.)

A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid. In this case, benzoic acid (weak acid) and sodium benzoate (conjugate base) form a buffer that can maintain a stable pH when mixed.

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the concentration of its acid and conjugate base. It is expressed as pH = pKa + log([A-]/[HA]), where pKa is the negative logarithm of the acid dissociation constant. This equation is essential for calculating the required concentrations of benzoic acid and sodium benzoate to achieve the desired pH.

Molarity (M) is a measure of concentration defined as moles of solute per liter of solution. To find the mass of sodium benzoate needed, one must first determine the number of moles required using the desired concentration and volume of the buffer solution. This can then be converted to mass using the molar mass of sodium benzoate, allowing for precise preparation of the buffer.