Video Transcript
What is the equation for the
solubility product of a generic inorganic compound with the formula MA?
We often think of substances as
being either soluble or insoluble in water. However, even substances that we
classify as insoluble may still be soluble in very small amounts. We can express this dissolution
using a generic equilibrium reaction. We can write the insoluble solid
compound as a reactant using the generic formula MA. The compound will react reversibly
in water to produce its constituent ions in solution, in this case the generic ions
M+ and A−.
When discussing solubility, we can
use a special equilibrium constant called the solubility product, which is
abbreviated as 𝐾 sp. The equations for equilibrium
constants are generally written as concentrations of the products divided by the
concentrations of the reactants. However, when writing the equation
for the 𝐾 sp, this reactant is an insoluble solid. The concentration of this solid
will not be included in the expression. So, we write the concentrations of
the products multiplied by each other.
We write the ions in brackets to
represent the measurement of their concentrations. The units for concentration are
often moles per liter. The concentrations of the products
would also be raised to the power of their stoichiometric coefficients. Since M+ and A− ions are present in
a one-to-one stoichiometric ratio in the reaction, it is not necessary to write
exponents of one. Therefore, the equation for the
solubility product of a generic inorganic compound with the formula MA is 𝐾 sp
equals the concentration of M+ times the concentration of A−.
