Unit 5 Cont Ksp

The Solubility Product Constant: All salts have different solubilities. Even ‘insoluble’ salts will dissolve in water to some extent. When a salt is dissolved in water, some of the salt dissolves and some may not. The amount of salt that dissociates into ions is different for every salt. Ksp is a number that represents how much of the salt will dissociate into ions.

The Solubility Product Constant: Ksp is equal to the product of the concentration terms each raised to the power of the coefficients of the substance in the dissociation equation. Ksp values @ 25oC can be found on the table on the next page. The equilibrium constant Ksp called the solubility constant indicates how soluble a substance is. If the Ksp is low, the solid is not very soluble. If the Ksp is high, the solid is soluble.

The Solubility Product Constant: An expression for the solubility product constant, Ksp, of calcium phosphate would be as follows: Balanced Equation: Ca3(PO4)2(s) ⇌ Ksp is equal to the product of the concentrations of the products, each raised to the power of the coefficient in the balanced equation, over the concentration of the reactant to the power of the coefficient. When using Ksp we do not include the concentrations of solids, liquids or gases, as they are not dissolved. Therefore, the concentration of the reactant should not be included, as it is a solid. Ksp =

The Solubility Product Constant: Example: Calculate the solubility product constant for calcium fluoride at 20oC given that it`s solubility is 1.6 × 10−2 g/L.  First write the chemical equation: Then convert to molarity (the number of moles of CaF2 that dissolved in 1L): Find Ksp using solubility constant expression:  

Determining Individual Ion Concentration from Ksp:  Ex. Calculate the concentrations of barium ions and sulphate ions in a saturated aqueous solution of barium sulphate at 25oC.

Determining Individual Ion Concentration from Ksp:  Ex. When 10.0 L of a saturated solution of magnesium carbonate, at 22°C is evaporated to dryness, 0.12g of solid magnesium carbonate is obtained. Calculate the Ksp of magnesium carbonate.

Determining Individual Ion Concentration from Ksp: Ex. A saturated solution of ionic calcium hydroxide has a hydroxide ion concentration of 3.0×10-3mol/L. Calculate the Ksp of calcium hydroxide at the same temperature.

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