Chemistry stoichiometry help please!

Question

determine the concentration of a solution of phosphoric acid if 25mL of the phosphoric acid requires 28.7mL of 0.125mol/L calcium hydroxide for complete neutralization.

Answer 1

Balanced equation

2H₃PO₄ + 3Ca(OH)2 ==> Ca₃(PO₄)2 + 6H₂O

moles Ca(OH)₂ = 0.0287 L x 0.125 mol/L = 0.003588 moles

moles H₃PO₄ = .003588 mol x 2/3 = .002392 moles

[H₃₃PO₄ = 0.002392 moles/0.025 L = 0.09567 M = 0.096 M