0.10 mole of solid calcium hydroxide is added to 1.00 liter of a 0.50 M solution of hydrochloric acid. After the reaction is complete, the hydrogen ion concentration of the solution will be:

Question

A) 0.40 M

B) 0.10 M

C) 0.20 M

D) 0.050 M

E) 0.30 M

Please explain and show work! I've been stuck on this problem for ages

Answer 1

Ca(OH)2 + 2HCl ==>. CaCl2 + 2 H2O

mol Ca(OH)2 = 0.1 moles

moles HCl = 1 L x 0.5 mol/L = 0.5 moles

So if you look at the balanced equation, it takes 2 moles HCl for each 1 mole of Ca(OH)2. So lets see how much HCl is left over after the reaction.

0.1 moles Ca(OH)2 x 2 mol HCl/mol = 0.2 mol HCl used

moles HCl left = 0.5 - 0.2 = 0.3 mol HCL

Assuming the volume didn’t change upon addition of the solid, we have 0.3 mol HCl/1 L.

Since HCl is strong, the concentration of H+ is also 0.3 M

pH = -log [H+] = - log 0.3 = 0.522