Introduction

Molar solubility is an essential concept in the study of chemistry. It is used to determine the maximum concentration of a solute that can dissolve in a solution before the solution becomes saturated. This article will guide you through the process of calculating molar solubility step-by-step, using practical examples and formulas that can be applied to any soluble compound.

Step 1: Identify the Solubility Product Constant (Ksp)

The first step in calculating molar solubility is to identify the Ksp value for the compound being dissolved. The solubility product constant (Ksp) represents the equilibrium between a solid and its constituent ions in a saturated solution. The higher the Ksp, the more soluble the compound. You can find Ksp values in standard chemistry reference tables or textbooks.

Step 2: Write the Dissociation Equation

Write down the balanced chemical equation for the dissociation of the solid into its constituent ions in equilibrium with the dissolved form. For example, if we are calculating the molar solubility of silver chromate (Ag2CrO4), we would write:

Ag2CrO4 (s) ⇌ 2Ag⁺ (aq) + CrO₄²⁻ (aq)

Step 3: Set Up and Solve for Molar Solubility

Using the dissociation equation, define variables for the concentrations of each ion at equilibrium. Then, express Ksp in terms of these variables and solve for molar solubility.

In our example:

– Let ‘s’ represent molar solubility.

– At equilibrium, [Ag⁺] = 2s and [CrO₄²⁻] = s.

Now express Ksp in terms of ‘s’:

Ksp = [Ag⁺]²[CrO₄²⁻] = (2s)²(s)

Using the Ksp value for silver chromate, which is 1.1 x 10⁻¹²:

1.1 x 10⁻¹² = (2s)²(s)

Solve the equation to find ‘s’:

s ≈ 7.1 x 10⁻⁵

Thus, the molar solubility of silver chromate in water is approximately 7.1 x 10⁻⁵ mol/L.

Conclusion

Calculating molar solubility involves identifying the Ksp value for a given compound, writing the dissociation equation, and setting up an equation to solve for molar solubility based on the Ksp expression. By following these steps, you can easily determine the molar solubility for any soluble compound and expand your understanding of equilibrium and solubility concepts in chemistry.