Question

If 15.0 mL of phosphoric acid completely neutralizes 38.5 mL of 0.150 mol/L calcium hydroxide, what is the concentration of the phosphoric acid?

Answer 1

2H₃PO₄ + 3Ca(OH)₂ = Ca₃PO₄ + 6H₂O

According to the equation, n (H₃PO₄) = 2/3 n (Ca(OH)₂).

C_M = n / V

n (Ca(OH)₂) = 0.150 x 0.0385 = 0.006 mol

n (H₃PO₄) = 2/3 x 0.006 = 0.004 mol

C_M (H₃PO₄) = 0.004 / 0.015 = 0.26 M