You have a 250.-mL sample of 1.250 M acetic acid (K_a = 1.8 $\times$ 10^-⁵).Assuming no volume change,how much NaOH must be added to make the best buffer?

Question

Quizplus · Accepted Answer

To make the best buffer, the concentration of the weak acid and its conjugate base should be equal. The concentration of acetic acid is 1.250 M. Therefore, the concentration of acetate ion should also be 1.250 M. To achieve this, we need to add enough NaOH to neutralize half of the acetic acid. The balanced chemical equation for the reaction is:CH3COOH + NaOH → CH3COONa + H2OFrom the equation, we can see that 1 mole of acetic acid reacts with 1 mole of NaOH. Therefore, we need to add 125 mL of 1.250 M NaOH to neutralize half of the acetic acid. This will give us a solution that contains 125 mL of 1.250 M acetic acid and 125 mL of 1.250 M acetate ion, which is the best buffer.The mass of NaOH required is:mass = volume × density × molaritymass = 125 mL × 1.00 g/mL × 1.250 mol/Lmass = 16.3 gTherefore, the correct answer is C) 16.3 g.

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