A 25.0-mL volume of a sodium hydroxide solution requires 19.6 mL of a 0.189 M hydrochloric acid for neutralization. A 10.0-mL volume of a phosphoric acid solution requires 34.9 mL of the sodium hydroxide solution for complete neutralization. Calculate the concentration of the phosphoric acid solution.

Verified step by step guidance

1. Write the balanced chemical equation for the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl): \[ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]
2. Use the stoichiometry of the reaction to determine the moles of NaOH in the 25.0 mL solution using the moles of HCl: \[ \text{Moles of HCl} = 0.189 \text{ M} \times 0.0196 \text{ L} \]
3. Calculate the concentration of the NaOH solution using the moles of NaOH and the volume of the NaOH solution: \[ \text{Concentration of NaOH} = \frac{\text{Moles of NaOH}}{0.0250 \text{ L}} \]
4. Write the balanced chemical equation for the reaction between phosphoric acid (H₃PO₄) and sodium hydroxide (NaOH): \[ \text{H}_3\text{PO}_4 + 3\text{NaOH} \rightarrow \text{Na}_3\text{PO}_4 + 3\text{H}_2\text{O} \]
5. Use the stoichiometry of the reaction to calculate the concentration of the phosphoric acid solution using the moles of NaOH and the volume of the phosphoric acid solution.

Key Concepts

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. In this context, sodium hydroxide (NaOH) acts as the base, while hydrochloric acid (HCl) and phosphoric acid (H3PO4) are the acids. Understanding the stoichiometry of these reactions is crucial for calculating concentrations, as the moles of acid must equal the moles of base at the equivalence point.

Molarity (Concentration)

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (M). In this problem, the molarity of hydrochloric acid is given, and it is used to determine the moles of HCl that react with NaOH, which is essential for finding the concentration of the phosphoric acid solution.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. It allows us to relate the volumes and concentrations of the reactants used in the neutralization reactions. By applying stoichiometric principles, we can determine the moles of phosphoric acid from the moles of sodium hydroxide used, leading to the calculation of its concentration.