Question

A 4.60 mLmL sample of an H3PO4H3PO4 solution of unknown concentration is titrated with a 1.050×10⁻² MNaOHMNaOH solution. A volume of 7.02 mLmL of the NaOHNaOH solution was required to reach the equivalence point.

What is the concentration of the unknown H3PO4H3PO4 solution?

Express your answer with the appropriate units.

Answer 1

Solution:

The complete neutralization reaction between NaOH and H3PO4 is given as,

3NaOH + H3PO4 = Na3PO4 + 3H2O

Since, 1 mol of H3PO4 required 3 mol of NaOH.

Hence, according to molarity equation,

M1V1 = 3 M2V2

Where,

M1 = Molarity of NaOH = 1.050 x 10^-2 M = 0.01050 M

V1 = Volume of NaOH = 7.02 mL

M2 = Molarity of H3PO4 = ?

V2 = Volume of H3PO4 = 4.60 mL

Therefore,

0.01050 M x 7.02 mL = 3 x M2 x 4.60 mL

M2 = 0.01050 M x 7.02 mL / 3 x 4.60 mL

M2 = 0.00534 M = 5.34 x 10^-3 M

Hence, the conentration of H3PO4 = 5.34 x 10^-3 M