Question

A 26.00 mL sample of an unknown H3PO4solution is titrated with a 0.130 M NaOH solution. The equivalence point is reached when 24.93 mLof NaOH solution is added.

What is the concentration of the unknown H3PO4 solution? The neutralization reaction is

H3PO4(aq)+3NaOH(aq)→3H2O(l)+Na3PO4(aq)

Answer 1

Number of moles of NaOH = molarity * volume of solution in L

Number of moles of NaOH = 0.130 * 0.02493 = 0.00324 mole

from the balanced equation we can say that

3 mole of NaOH requires 1 mole of H3PO4 so

0.00324 mole of NaOH will require

= 0.00324 mole of NaOH *(1 mole of H3PO4 / 3 mole of NaOH )

= 0.00108 mole of H3PO4

molarity of H3PO4 = number of moles of H3PO4 / volume of solution in L

molarity of H3PO4 = 0.00108 / 0.026 L = 0.0415 M

Therefore, concentration of H3PO4 = 0.0415 M