Acid-Base Titrations

AP Chemistry· difficulty 1/5

A student titrates 25.00 mL of 0.100 M acetic acid with 0.100 M NaOH while monitoring pH. Selected pH values: at 0.00 mL added, pH = 2.87; at 12.50 mL (half-equivalence), pH = 4.74; at 25.00 mL (equivalence), pH = 8.72.

Why is the equivalence pH greater than 7?

A
$Excess NaOH is present at equivalence$
B
$The solution at equivalence is sodium acetate, whose acetate ion hydrolyzes to give OH-$
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C
$All titration equivalence points are basic$
D
$Acetic acid is a strong acid$

Explanation

At equivalence the solution contains the salt of a weak acid (NaCH3COO). The acetate ion is a weak base (CH3COO- + H2O <-> CH3COOH + OH-), giving pH > 7.

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