The key difference between solubility and solubility product is that the solubility describes the dissolution of a substance in a solvent whereas the solubility product describes the mathematical product of the dissolved ion concentrations raised to the power of their stoichiometric coefficients.
According to the difference mentioned above, solubility and solubility product are two related terms. Therefore, we can use the solubility product of a substance to understand the solubility of that substance; the smaller the solubility product, the lower the solubility.
CONTENTS
1. Overview and Key Difference
2. What is Solubility
3. What is Solubility Product
4. Side by Side Comparison – Solubility vs Solubility Product in Tabular Form
5. Summary
What is Solubility?
Solubility is the property of a substance to dissolve in a solvent. Here, we call the substance (which dissolve in the solvent) as the “solute”. It can be a solid, liquid or a gaseous substance. Solvent, on the other hand, can also be in solid, liquid or gaseous state. The solubility of a substance depends on the chemical and physical properties of both solute and solvent. Moreover, it depends on the external factors of the solute-solvent system; temperature, pressures, etc.
Figure 01: Formation of a Solution from the Dissolution of a Solute in a Solvent
A substance can dissolve in a suitable solvent until the solvent get saturated from that substance. It is the maximum amount of solute molecules that the solvent can hold at the provided temperature and pressure. In contrast, insolubility is being unable to dissolve in the substance. However, solubility does not describe the ability to dissolve a substance because we can dissolve substances via chemical reactions as well. The factors affecting the solubility of a solute are as follows:
- Temperature
- Pressure
- Presence of other chemicals
- The polarity of the solute and solvent
- Intermolecular forces between solute and solvent
- pH
- size of solute molecules
What is Solubility Product?
Solubility product is the mathematical derivation that shows the equilibrium between dissolved and undissolved species of a substance in a solvent. Therefore, it represents the level at which a solute dissolves in a solution. More precisely, it is the mathematical product of its dissolved ion concentrations raised to the power of their stoichiometric coefficients.
Solubility product is a constant value for a certain substance at a particular temperature and pressure. Therefore we call it the “solubility product constant”. We can denote it as Ksp. This term is directly related to the solubility of a substance; higher the Ksp, higher the solubility. Moreover, it is a heterogeneous equilibrium constant. We use this term with solutions that are saturated with a particular solute. This constant always depends on the temperature. Let us consider an example to get an idea about it.
aA(s) ↔ bB(aq) + cC(aq)
The above system has dissolved B and C products and undissolved A as well. Then the solubility product constant is as follows:
Ksp = [B]b.[C]c
What is the Difference Between Solubility and Solubility Product?
Solubility is the property of a substance to dissolve in a solvent. Simply, it describes the dissolution of a substance in a solvent. Solubility product is the mathematical derivation that shows the equilibrium between dissolved and undissolved species of a substance in a solvent. This term describes the mathematical product of the dissolved ion concentrations raised to the power of their stoichiometric coefficients. This is the key difference between solubility and solubility product. Moreover, these two terms relate to each other because the solubility product of a substance describes the solubility of that substance.
Summary – Solubility vs Solubility Product
Solubility and solubility product are two related terms. The difference between solubility and solubility product is that solubility the describes the dissolution of a substance in a solvent whereas the solubility product describes the mathematical product of the dissolved ion concentrations raised to the power of their stoichiometric coefficients.
Reference:
1. “Solubility.” Wikipedia, Wikimedia Foundation, 27 July 2018. Available here
2. Libretexts. “Solubility Product Constant, Ksp.” Chemistry LibreTexts, Libretexts, 21 July 2016. Available here