Final answer:
To prepare an acetate buffer at pH 4.76 with 0.1 M sodium acetate, you would add acetic acid, which, when combined in equimolar amounts with sodium acetate, creates the desired buffer.
Step-by-step explanation:
To make an acetate buffer at pH 4.76, starting with 500 mL of 0.1 M sodium acetate, you would need to add CH₃COOH (acetic acid). This is because a buffer solution is composed of a weak acid and its conjugate base. Since sodium acetate (CH₃COONa) acts as the conjugate base, the addition of its corresponding weak acid, acetic acid, will establish the buffer system at the desired pH level. According to the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the pKa of the acid and the ratio of the concentrations of the conjugate base and acid, it is essential to maintain a ratio that will give a pH equal to the pKa of the acid.
In this case, the pKa of acetic acid is given as 4.76. Therefore, for the solution to have a pH of 4.76, you should have equimolar amounts of acetic acid and sodium acetate. Since you already have 0.1 M sodium acetate in the solution, you would need to add the corresponding amount of acetic acid to achieve the desired buffer capacity.