A saturated aqueous solution of calcium hydroxide has a pH of 12.25. What is the [Ca 2+] of such a
solution?
Never mind I got it!
To calculate the concentration of Ca2+, we need to determine the concentration of OH- in the saturated aqueous solution of calcium hydroxide.
Since calcium hydroxide is a strong base, it dissociates completely in water to form one Ca2+ ion and two OH- ions. Therefore, the concentration of OH- ions is twice the concentration of Ca2+ ions.
Given that the pH of the solution is 12.25, we can determine the concentration of OH- ions using the following equation:
pOH = 14 - pH
pOH = 14 - 12.25 = 1.75
Now, we can convert the pOH to concentration of OH- using the equation:
[OH-] = 10^(-pOH)
[OH-] = 10^(-1.75)
[OH-] = 0.0178 M
Since the concentration of OH- is twice the concentration of Ca2+, the concentration of Ca2+ can be calculated as:
[Ca2+] = 0.0178 M / 2
[Ca2+] = 0.0089 M
Therefore, the concentration of Ca2+ in the saturated aqueous solution of calcium hydroxide is 0.0089 M.
To determine the concentration of Ca2+ in a saturated aqueous solution of calcium hydroxide, we need to understand the dissociation of calcium hydroxide in water.
The balanced chemical equation for the dissociation of calcium hydroxide is:
Ca(OH)2(s) ⇌ Ca2+(aq) + 2OH-(aq)
Since the solution is saturated, it means that it contains the maximum amount of dissolved calcium hydroxide possible at that temperature.
In a saturated solution, the concentration of Ca2+ is generally determined by the solubility product constant (Ksp) of calcium hydroxide. The Ksp expression for calcium hydroxide is:
Ksp = [Ca2+][OH-]^2
However, we can assume that the concentration of OH- is approximately equal to the concentration of Ca2+ since calcium hydroxide is a strong base.
Therefore,
Ksp = [Ca2+][OH-]^2 ≈ [Ca2+] [Ca2+]^2 = [Ca2+]^3
Taking the cube root of Ksp gives us the concentration of Ca2+:
[Ca2+] ≈ ∛Ksp
To find the concentration of Ca2+, we need to know the value of Ksp for calcium hydroxide, usually given in the literature. The Ksp constant for calcium hydroxide at 25°C is approximately 5.5 x 10^-6.
Using this value, we can calculate the concentration of Ca2+:
[Ca2+] ≈ ∛(5.5 x 10^-6)
[Ca2+] ≈ 0.018 M
Therefore, the approximate concentration of Ca2+ in a saturated aqueous solution of calcium hydroxide is 0.018 M.