We calculate for the number of moles of calcium hydroxide Ca(OH)2 which is equal to number of moles of phosphoric acid H3PO4 at equivalence point:
mol Ca(OH)2 = 0.0360L Ca(OH)2 (1.0mol Ca(OH)2 /1L Ca(OH)2)
= 0.0360 mol
From the equation for the acid base reaction written as
2H3PO4 + 3Ca(OH)2 → Ca3(PO4)2 + 6H2O
we use the mole ratio of ammonia and nitrogen dioxide from their coefficients, which is 2 moles of phosphoric acid is to react with 3 moles of calcium hydroxide, to compute for the number of moles of H3PO4:
mol H3PO4 = 0.0360mol Ca(OH)2 (2mol H3PO4/3mol Ca(OH)2)
= 0.0240 mol
Dividing the number of moles of H3PO4 by the number of liters, the molar concentration of H3PO4 is therefore
[H3PO4] = 0.0240mol / 0.011L
= 2.18 M
