Question

A sample of an aqueous solution of 0.3467 M NaOH is neutralized by 34.87 mL of 0.1792 M H₃PO₄ according to the reaction below. Determine the volume of the sodium hydroxide solution.

a) 10.92 mL
b) 34.87 mL
c) 69.74 mL
d) 104.61 mL

Answer 1

The volume of 0.3467 M NaOH solution needed to neutralize 34.87 mL of 0.1792 M H₃PO₄ is 69.74 mL. This is calculated using the stoichiometry of the balanced chemical equation and the given molarities of the reactants.

Step-by-step explanation:

To determine the volume of sodium hydroxide solution needed to neutralize a given volume and concentration of H₃PO₄, we must first write the balanced chemical equation for the reaction. For strong bases like NaOH neutralizing phosphoric acid, the reaction is typically:

3 NaOH + H₃PO₄ → Na₃PO₄ + 3 H₂O

Using the stoichiometry of the reaction, where three moles of NaOH are required for every mole of H₃PO₄, and the provided concentrations, we can calculate the volume of NaOH needed:

M₁V₁ = M₂V₂ (where M₁ and V₁ are the molarity and volume of H₃PO₄, and M₂ and V₂ are the molarity and volume of NaOH, respectively).

By rearranging the formula to solve for V₂, we get:

V₂ = (M₁V₁) / M₂

Since the reaction ratio is 1:3 H₃PO₄ to NaOH, we adjust M₁V₁ accordingly:

V₂ = (3 × M₁V₁) / M₂

V₂ = (3 × 0.1792 M × 34.87 mL) / 0.3467 M

V₂ = 69.74 mL

This calculation reveals that 69.74 mL of the 0.3467 M NaOH solution is needed to completely neutralize 34.87 mL of 0.1792 M H₃PO₄. Therefore, the correct answer is c) 69.74 mL.