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27. Preparation of Buffer of Known pH and Strength Given 0.10 M solutions of acetic acid (pK₁ = 4.76) and sodium acetate, describe how you would go about preparing 1.0 L of 0.10 M acetate buffer of pH 4.00. Answer Use the Henderson-Hasselbalch equation to calculate the ratio [Ac /[HAc] in the final buffer. pH=pK₂ + log ([Ac V[HAC]) log ([Ac 1/[HAc]) = pH - pK₂ = 4.00 4.76 = -0.76 [Ac V[HAC] = 10-0.76 A-/HA= antilog -0.76 HA/A-=antilog +0.76 HA/A-= 5.75 HA/A- = 5.75/1 HA=5.75/6.75 = 0.85 A = 1/6.75 = 0.15 The fraction of the solution that is Ac = [Ac /[HAC + Ac] = 10-0.76/(1+ 10-0.76) = 0.148, which must be rounded to 0.15 (two significant figures). Therefore, to make 1.0 L of acetate buffer, use 150 mL of sodium acetate and 850 mL of acetic acid.