The Ksp value is calculated from the concentrations of the products of Ca(OH)2 when the compound is added to an aqueous solution. Calculating the value requires knowing those concentrations, the balanced equation for the solution and plugging in those values to the equation Ksp = [C]^c * [B]^b.
- Find the balanced equation
When added to an aqueous solution, the compound Ca(OH)2, calcium hydroxide, ionizes to form the Ca^2+ and OH-. Write out the equation as Ca(OH)2 <===> Ca2+ + 2OH-, since there are two ions of OH- for every ion of Ca2+.
- Find the concentrations of the products
The concentration of each product is found by dividing the number of moles of each ion over the total liters of solution created. For example, in a 25 milliliter solution, there are 0.00056 moles of OH-. Divide 0.00056 moles over 0.025 liters to get the concentration [OH-] as 0.0225 moles per liter.
- Plug the values into the formula
The equation for the Ksp of Ca(OH)2 is the concentration [Ca2+] times the concentration [OH-] taken to the second power, since the OH- has a coefficient of 2 in the balanced equation. Plug the concentrations of each of the products into the equation to calculate the value of Ksp.