What mass of sodium acetate should be dissolved in 250.0 mL of 0.30 M aqueous acetic acid to form a buffer of pH 5.0? (K_a for acetic acid is 1.8 × 10^-5) A)11 g B)8.0 g C)7.5 g D)5.0 g E)1.4 g

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Quizplus · Accepted Answer

To solve this, we use the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the acetate ion and [HA] is the concentration of acetic acid. Given that the pH is 5.0 and the pKa (which is -log(Ka)) for acetic acid is 4.74 (since Ka = 1.8 × 10^-5), we can set up the equation as follows: 5.0 = 4.74 + log([A-]/[0.30]). Solving for [A-] gives a concentration of about 0.48 M. To find the mass of sodium acetate (NaC2H3O2) needed, we use the formula mass = molarity × volume × molar mass. The molar mass of sodium acetate is approximately 82.03 g/mol. Thus, mass = 0.48 mol/L × 0.250 L × 82.03 g/mol ≈ 9.85 g, which is closest to 11 g, option A.

What Mass of Sodium Acetate Should Be Dissolved in 250