Question

2 H3PO4(aq) + 3Ca(OH)2(aq) = Ca3(PO4)2 (s) + 6 H2O(l)

1.

a.Calculate the volume of .0500 M phosporic acid that would be required to exactly react with 20.0 ml of 0.100 M calcium Hydroxide

b. What mass of calcium phosphate will precipitate?

Answer 1

no of moles of no of moles of Ca(OH)2 = 0.1 x 0.02 = 0.002 moles

from the balanced equation it is clear that

one mole of calcium hydroxide required 2/3 mole of phosphoric acid

so 0.002 moles require 0.002 x 2/3 = 0.0013 moles of phospharic acid required

now we know the moles of H3PO4 and we know the molarity we can calculate the volume

volume of H3PO4 = 0.0013 / 0.05

= 0.0267 Liters or 26.67 ml

1 moles of Ca(OH)3 is producing 1/3 mole of Ca3(PO4)2

0.002 moles will produce 0.002 /3 moles of Ca3(PO4)2 = 6.67 x 10^-4

no of moles = weight /molar mass

weight = 6.67 x 10^-4 x 310.2 = 0.207 grams