How many mL of 2.50 M calcium hydroxide solution is needed to completely neutralize 0.225 L of 2.50 M phosphoric acid?

Answer 1

First, write the balanced equation for the reaction taking place:

3Ca(OH)₂ + 2H₃PO₄ ==> Ca₃(PO₄)₂ + 3H₂O ... balanced equation

Find moles H3PO4 present:

0.225 L x 2.50 mols/L = 0.5625 mols

Calculate mols Ca(OH)2 needed (use the balanced equation to do this):

0.5625 mols H3PO4 x 3 mols Ca(OH)2 / 2 mols H3PO4 = 0.8438 mols Ca(OH)2

Finally, convert this to mls of Ca(OH)2:

(x L)(2.50 mol/L) = 0.8438 mols

x = 0.3375 L = 337.5 mls = 338 mls (3 sig. figs.)