A 135.0-mL sample of a 0.25 M solution of H₃PO₄ is titrated with 0.12 M NaOH. What volume of base must be added to reach the third equivalence point?

Question

Quizplus · Accepted Answer

The titration of a triprotic acid requires three equivalence points. The third equivalence point represents the point at which all three protons have been neutralized by the added base. In order to calculate the volume of base required to reach this point, we need to first calculate the moles of acid present in the initial solution. moles of acid = Molarity x Volume (in liters) moles of acid = 0.25 M x 0.135 L moles of acid = 0.03375 mol H₃PO₄ Since there are three protons in H₃PO₄, the number of moles of base required to reach the third equivalence point will be three times the number of moles of acid. moles of base required = 3 x moles of acid moles of base required = 3 x 0.03375 mol moles of base required = 0.10125 mol NaOH Now we can use the concentration of NaOH and the number of moles required to calculate the volume of base needed to reach the third equivalence point. volume of base required = moles of base required / Molarity of NaOH volume of base required = 0.10125 mol / 0.12 M volume of base required = 0.84375 L = 843.75 mL The answer is 8.4 F1F1F1S1F1F1F10 10² mL.

A 1350-ML Sample of a 0