CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Phosphoric acid, a triprotic acid, is titrated with aqueous sodium hydroxide. 50.0 mL of 0.100 M H₃PO₄ is placed in a flask. A buret delivers 25.0 mL of 0.150 M NaOH into the acid solution, and the contents are mixed thoroughly.
(a) Calculate the initial number of moles of H₃PO₄ and NaOH present before the reaction occurs.
(b) Determine the principal phosphate species (e.g., H₂PO₄⁻, HPO₄²⁻, PO₄³⁻) that remain in solution after reaction is complete. Justify your answer with stoichiometric reasoning.
(c) Write the balanced net ionic equation that represents the reaction occurring between the acid and the base under these conditions.
(d) Phosphoric acid is considered weak in each of its three ionization steps. Explain how this acid strength influences the form of the net ionic equation you wrote in part (c).