A saturated aqueous solution of calcium hydroxide is approximately 0.13% calcium hydroxide, by mass, and has a density of 1.02 g ml-1. What is the pH of such a solution?
A) 11.95
B) 12.25
C) 12.55
D) 12.75
E) 13.00

Question

Quizplus · Accepted Answer

First, we need to find the concentration of hydroxide ions in the solution. Calcium hydroxide is a strong base, so it will dissociate completely in water:

Ca(OH)2→Ca2+(aq)+2OH−(aq)

The concentration of hydroxide ions will be twice the concentration of calcium hydroxide:

[OH−]=2×0.13%=2.6×10−3M

Next, we can use the fact that Kw=[H+][OH−]=1.0×10−14 to find the concentration of hydrogen ions:

[H+]=Kw[OH−]=(1.0×10−14)/(2.6×10−3)=3.85×10−12M

Finally, we can use the definition of pH to find the pH of the solution:

pH=−log[H+]=−log(3.85×10−12)=12.55

Therefore, the answer is C.

A Saturated Aqueous Solution of Calcium Hydroxide Is Approximately 0