Problem: A 31.00 mL sample of an unknown H3PO4 solution is titrated with a 0.120 M NaOH solution. The equivalence point is reached when 26.43 mL of NaOH solution is added. What is the concentration of the unknown H3PO4 solution? The neutralization reaction is H3PO4 (aq) + 3 NaOH(aq) → 3 H2O(l) + Na3PO4(aq)

FREE Expert Solution

Recall that at the equivalence point of a titration:

Also, recall that moles = molarity × volume

This means:

$\overline{){\left(\mathbf{MV}\right)}_{{\mathbf{acid}}}{\mathbf{=}}{\left(\mathbf{MV}\right)}_{{\mathbf{base}}}}$

Correct the concentration depending on the number of acidic or basic ions present:

For acids: Multiply by the number of H+ ions

For bases: Multiply by the number of OH, H, O2–, or NH2 ions

Solving for Macid:

• There are 3 H+ ions in H3PO4:

Problem Details

A 31.00 mL sample of an unknown H3PO4 solution is titrated with a 0.120 M NaOH solution. The equivalence point is reached when 26.43 mL of NaOH solution is added. What is the concentration of the unknown H3PO4 solution? The neutralization reaction is H3PO4 (aq) + 3 NaOH(aq) → 3 H2O(l) + Na3PO4(aq)