What is the common ion effect

Difference between Ksp and Qsp

Key difference - Ksp vs. Qsp

Ksp is the solubility product constant and Qsp is the solubility product quotient. The Main difference between Ksp and Qsp is that Ksp indicates the solubility of a substance, while Qsp indicates the current state of a solution. The solubility product is the product of concentrations of ionic species present in a solution when a substance is dissolved in a solvent such as water.

The solubility product is determined when the solution is saturated with this substance. The solubility product quotient is the product of the concentrations of ionic species in a solution at any given time; before saturation or after the solution is saturated. It is sometimes referred to as the ionic product.

CONTENT

1. Overview and key difference
2. What is Ksp
3. What is Qsp?
4. Relationship between Ksp and Qsp
5. Side-by-side comparison - Ksp vs. Qsp in tabular form
6. Summary

What is Ksp?

Ksp is the solubility product constant of a particular substance. It shows the solubility of a substance (how much solid is dissolved in a solution). The solubility product constant is given for a solution that is saturated with a substance. The higher the Ksp value, the higher the solubility of this substance. The solubility product is given as the product of concentrations of ionic species in a solution.

A saturated solution appears with turbidity, which indicates the beginning of precipitation. It is the insoluble form of the solute. The liquid part of this system contains the soluble solutes. The Ksp of this solution represents the balance between these soluble and insoluble forms.

The factors that affect the value of the solubility product constant are temperature, the presence of common ions, pH or acidity, etc. As the temperature is increased, the solubility of the solid precipitate also increases. Then the product of the concentrations of the ionic species increases, resulting in a high value of the solubility product. The presence of a common ion is described by the common ion effect. When a common ion is present, the Ksp will decrease. An ordinary ion means one of the ionic species already present in this solution. For example, for an equilibrium system using BaSO & sub4; (Barium sulfate) together with Ba+2 Ions and SO42- Ions, the addition of either Ba+2 or so42- Ions can affect the equilibrium.

BaSO4 (s)↔ Ba+2(aq) + SO42-(aq)

Figure 01: Ksp of a saturated BaSO4 solution

When one of these ions is added from an external source, the above equilibrium shifts to the left (a more insoluble form of the substance is formed, which reduces the amount of ions present in the solution), thereby decreasing the solubility of that substance.

What is Qsp?

Qsp is the solubility product quotient of a solution. It describes the current status of a solution. This means that Qsp is given for an unsaturated (before saturation), saturated or supersaturated solution. The Qsp is also known as the ion product because at any point in time (not at a specific point in time like saturation) it is the product of concentrations of ionic species. Hence, Ksp (the solubility product constant) is a special form of Qsp.

What is the relationship between Ksp and Qsp ??

  • If the Qsp value for a substance in a solution is below the Ksp value, more solids can be dissolved in that solution.
  • If Qsp and Ksp have the same values, the solution is saturated.
  • When Qsp is higher than the value of Ksp, a precipitate is formed.

What is the difference between Ksp and Qsp?

Ksp vs Qsp

Ksp is the solubility product constant of a particular substance.Qsp is the solubility product quotient of a solution.
nature
Ksp is an equilibrium value.Qsp is not an equilibrium value.
State of the solution
Ksp is the product of concentrations of ionic species in a saturated solution.Qsp is the product of concentrations of ionic species in an unsaturated, saturated or supersaturated solution.

Summary -Ksp vs. Qsp

Ksp and Qsp are very related terms in chemistry. Ksp is defined as a saturated solution that has an equilibrium between ionic species and a solid precipitate (the moment a precipitate began to form). Qsp is given for each moment (not given); before saturation or after saturation. The difference between Ksp and Qsp is that Ksp is the solubility product constant while Qsp is the solubility product quotient.

Reference:

1. "heterogeneous equilibria". Solubility products and ionic products.Available here