Question

Before the first endpoint only K₃PO₄ is reacting.

PO₄^3–_(aq) + H₃O⁺_(aq) -----> HPO₄^2–_(aq) + H₂O _(l)

If at the first equivalence point 14.91 ml of 0.1206 M HCl is consumed, how many mmol of K₃PO₄ were present in the sample? Round your answer to 3 decimal places.

Answer 1

mmol of K₃PO₄ present = 1.798 mmol

Explanation

At first equivalence point, the reaction between HCl and K₃PO₄ is given as

HCl (aq) + K₃PO₄ (aq) K₂HPO₄ (aq) + KCl (aq)

Given : molarity of HCl = 0.1206 M

volume of HCl = 14.91 mL

mmoles of HCl = (molarity of HCl) * (volume of HCl (mL))

mmoles of HCl = (0.1206 M) * (14.91 mL)

mmoles of HCl = 1.798 mmol

From the reaction equation, mmol of K₃PO₄ present = mmol of HCl consumed

or mmol of K₃PO₄ present = 1.798 mmol