A 30.00-mL sample of an unknown H₃PO₄ solution is titrated with a 0.100 M NaOH solution. The equivalence point is reached when 26.38 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)

Verified step by step guidance

1. Determine the total moles of NaOH used in the titration. Use the formula: moles = concentration (M) imes volume (L). Convert the volume of NaOH from mL to L by dividing by 1000.
2. From the balanced chemical equation, H₃PO₄(aq) + 3 NaOH(aq) → 3 H₂O(l) + Na₃PO₄(aq), note that 1 mole of H₃PO₄ reacts with 3 moles of NaOH. Calculate the moles of H₃PO₄ by dividing the moles of NaOH by 3.
3. Calculate the concentration of the H₃PO₄ solution. Use the formula: concentration (M) = moles of solute / volume of solution (L). Convert the volume of the H₃PO₄ solution from mL to L by dividing by 1000.
4. Ensure the units are consistent when performing the calculations to avoid any errors in the final concentration.
5. Check your calculations for any possible arithmetic errors to ensure the accuracy of the concentration of the H₃PO₄ solution.

Key Concepts

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant, a solution of known concentration, to a sample until the reaction reaches its equivalence point, where the amount of titrant equals the amount of substance in the sample. This method is commonly used in acid-base reactions to find the concentration of an unknown acid or base.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows chemists to determine the relationships between the quantities of substances involved in a reaction. In this case, the stoichiometry of the reaction between phosphoric acid (H3PO4) and sodium hydroxide (NaOH) indicates that one mole of H3PO4 reacts with three moles of NaOH, which is crucial for calculating the concentration of the unknown solution.

Molarity

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 titration problem, the molarity of the NaOH solution is given, and by using the volume of NaOH added at the equivalence point, one can calculate the moles of NaOH used, which can then be related back to the moles of H3PO4 to find its concentration.