Question

What is the pH of a solution prepared by mixing 50.0 mL of 0.010 mol/L HCl(aq) and 50.0 mL of 0.010 mol/L Ca(OH)2(aq)? Assume the temperature
is 25 degrees Celsius. Additional information given: Kw = 1.0×10^−14 at 25 degrees Celsius.

The possible answers are:
A) 2.00
B) 2.30
C) 7.00
D) 11.70
E) 12.00

The correct answer is apparently D) 11.70, but I don't know how to come to that conclusion.

Any help would be greatly appreciated!

Answer 1

The correct answer is 11.69.
50 x 0.01 = 0.5 millimols each.
....Ca(OH)2 + 2HCl ==> CaCl2 + 2H2O
I....0.5......0.5.......0.......0
C..-0.25.....0.25.......0.5
C...0.25.......0........0.5
So [Ca(OH)2] = 0.25 mmols/100 mL = 0.0025 and (OH^-) = 2*that = 0.005M
You can take it from here.