Video: EC17-18-S1-Q45A

What is meant by the solubility product?

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Video Transcript

What is meant by the solubility product?

The solubility product is a property of a salt. It is usually used in reference to a salt that does not dissolve completely. Let’s take, for instance, calcium carbonate. When calcium carbonate is added to water, small amounts dissolve, producing aqueous calcium and carbonate ions. The equilibrium constant for this process is given the name “solubility product.”

The equilibrium product here contains only the concentrations of the ions, not of the starting solid, because its concentration is assumed to be constant. This is given the label Ksp. Solubility products are assumed to be taken at saturation, whereas much of the solid has dissolved as possible. This also assumes that there is sufficient solid material in order to saturate the solution. And therefore, it’s likely that the solid is in excess.

Let’s have a look at another example, that of the dissolving of barium phosphate. Here the solubility product is equal to the concentration of barium to the power of three multiplied by the concentration of phosphate to the power of two. As with any equilibrium constant expression, the concentration of a species is taken to the power of the coefficient of that species.

We now have all the information we need to write the answer in full sentences. What is meant by the solubility product? The solubility product is the product of the concentrations of the ions expressed in moles per litre of a dissolved salt raised to their stoichiometric coefficients at saturation.

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