1) Balanced equation:
3 Ca(OH)2(aq) +
2 H3PO4(aq) = 6
H2O(l) + Ca3(PO4)2(s)
2) Calculations
Moles
H3 PO4: ?
Ca[OH]2: 0.025 L * 0.0150 mol/L = 0.000375 mol
Ratios: 3 mol Ca[OH]2 / 2 mol H3PO4 = 0.000375 mol Ca[OH]2 / x mol H3PO4
=> x = 0.000375 * 2 /3 = 0.00025 mol Ca[OH]2
Volume of Ca[OH]2 = # of moles / Molarity = 0.00025 mol / 0.0300 mol/L = 0.00833 L = 8.33 mL
Answer: 8.33 mL