SOLUBILITY AND SOLUBILITY PRODUCT

OBJECTIVE

In this experiment you will determine the solubility and solubility product of a sparingly soluble salt, potassium hydrogen tartrate, and also in four solutions containing a common ion.

INTRODUCTION

When a salt of low dissolubility dissolves in water, equilibrium is established between the solid solute and the dissolved ions. There are two terms used in discussing this condition. The first is solubility, which is the maximum amount of salt that will dissolve in a given amount of solvent (usually water) at a specified temperature. Solubility is usually expressed in units of molarity (moles/L), but sometimes g solute/ g solvent is used. The second term is a solubility product, Ksp. This is a special equilibrium constant for the dissolving of a salt in water. By convention the equation for the reaction is always written with the solid as the reactant, and the ions as products. For a general salt, AmBn, the equation would be:

The equilibrium constant for such a salt would be:

The solubility product expression matches the coefficients in the equilibrium equation, and that the solid is not included in the Ksp equation.

In this experiment, you will determine the Ksp for the sparingly soluble salt potassium hydrogen tartrate (also called acid tartarate or bitartrate). It dissolves in water to give potassium ions and hydrogentartrate ions according to the following equation:

KHC4H4O6 K+ + HC4H4O6-

The solubility product is