If 23.6 mL of 0.200 M NaOH is required to neutralize 10.00 mL of a H3PO4 solution , what is the concentration of the phosphoric acid solution

The correct answer is 0.157 M.

Explanation:

The chemical equation of the mentioned reaction is, 3NaOH + H₃PO₄ ⇄ Na₃PO₄ + 3H₂O The molarity of NaOH given is 0.2 M, the volume of NaOH given is 23.6 ml or 23.6 × 10⁻³ L. The moles of NaOH can be determined by using the formula, Moles of NaOH = Volume of NaOH × Molarity Moles of NaOH = 23.66 × 10⁻³ L × 0.2 M = 0.00472 moles Based on the reaction, 3 moles of NaOH needs 1 mole of H₃PO₄. So, 0.00472 moles of NaOH will require, 0.00472/3 = 0.0015733 moles.

The concentration or molarity of the H₃PO₄ will be, [H₃PO₄] = Moles of H3PO4/Volume of H₃PO₄ in liters (Volume of H₃PO₄ given is 10 ml of 10 × 10⁻³L) = 0.0015733 moles/ (10 × 10⁻³ L) = 0.157 M