A 133.4-mL sample of a 0.21 M solution of H₃PO₄ is titrated with 0.14 M NaOH. What volume of base must be added to reach the third equivalence point? A) 4.0 × 10² mL B) 2.0 × 10² mL C) 6.0 × 10² mL D) 2.7 × 10² mL E) 67 mL

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Quizplus · Accepted Answer

To reach the third equivalence point, all three acidic hydrogens of H3PO4 must be neutralized. The moles of H3PO4 are 133.4 mL * 0.21 M = 0.028014 moles. Since each H3PO4 molecule can donate 3 protons, the moles of NaOH needed are 3 * 0.028014 = 0.084042 moles. The volume of 0.14 M NaOH needed is 0.084042 moles / 0.14 M = 600.3 mL, which is approximately 6.0 × 10^2 mL.

A 1334-ML Sample of a 0