Problem 87 - Chemistry: An Atoms-Focused Approach

Question

What is the difference between molar solubility and solubility product?

Step-by-Step Solution

Answer

Question: Explain the difference between molar solubility and solubility product. Answer: Molar solubility refers to the maximum concentration of a substance in a solution at equilibrium, measured in moles per liter (mol/L), while solubility product (Ksp) is the equilibrium constant for the dissolution-precipitation process, which is dimensionless. Molar solubility depends on the stoichiometry of the substance, whereas solubility product depends on the concentrations of the ions in the solution at equilibrium. Although both concepts describe the solubility of a substance, they are not identical and their numerical values may not be the same.

Step 1: Define Molar Solubility

Molar solubility refers to the maximum amount of a solute that can dissolve in a standard amount of solvent (usually 1 liter), measured in units of moles per liter (mol/L). This is the solubility of a substance at equilibrium, meaning that it has reached a point where the rate of dissolution equals the rate of precipitation. In other words, molar solubility represents the maximum concentration of a substance in a solution at equilibrium.

Step 2: Define Solubility Product

Solubility product, denoted by Ksp, is the equilibrium constant for a chemical reaction in which a solid substance dissolves into its constituent ions in a solution. It represents the balance between the dissolution of a solid and the precipitation of that solid back into its original form. The solubility product is mathematically expressed as the product of the concentrations of the ions raised to the power of their corresponding stoichiometric coefficients in a balanced chemical equation.

Step 3: Compare Molar Solubility and Solubility Product

Although both molar solubility and solubility product are related concepts that describe the solubility of a substance, they are not identical. Here are some differences between them: 1. Molar solubility is a measure of the maximum concentration of a substance in a solution at equilibrium, while solubility product is the equilibrium constant for the dissolution-precipitation process. 2. Molar solubility is expressed in terms of moles per liter (mol/L), whereas solubility product is dimensionless. 3. Molar solubility depends on the stoichiometry of the substance, while solubility product only depends on the concentrations of the ions in the solution at equilibrium. 4. The numerical values of molar solubility and solubility product may not be the same. For example, for a substance with the molecular formula A(s) <-> aA+(aq) + bB-(aq), the molar solubility (S) would be related to Ksp according to the relationship Ksp = (aS)^a*(bS)^b. In summary, molar solubility and solubility product are two different but related concepts that describe the solubility of a substance. While molar solubility measures the maximum concentration of a dissolved substance at equilibrium, solubility product is the equilibrium constant relating the concentrations of dissolved ions in the solution.