Answer to Question #28634 in Chemistry for Haley

Question

What is the concentration of a Ca(OH)2 solution if 15.0 ml of 0.500 M H3PO4 solution is required to completely neutralize 22.5 ml of the Ca(OH)2 solution?

Answer 1

3Сa(OH)₂ + 2H₃PO₄ = Ca₃(PO₄)₂ + 6H₂O
C(M) = v/V
C(M)-molar concentration of the solution;
v - molar mass, mole;
V - volume of the solution.
v = m/M
m - mass of the substance, grams;
M - molar mass of the substance.

From the task we know that 15.0 ml of 0.500 M H₃PO₄ solution is required to completely neutralize 22.5 ml of the Ca(OH)₂.
The amount of H₃PO₄ could be calculated as:
v = C(M) x V
v(H₃PO₄) = 0.5 x 0.015 = 0.0075 mol
According to the equation the total amount of Сa(OH)₂ is:
v(Сa(OH)₂) = v(H₃PO₄)/2*3 = 0.0075/2*3 = 0.011 mol

So the concentration of Сa(OH)₂ is:
C(Сa(OH)₂) = v/V = 0.011/0.0225 = 0.48 M