The solubility equation for SrSO4 involves its dissolution into ions and the corresponding solubility product constant (Ksp) expression, along with the relationship between Ksp and molar solubility (S).
Understanding Solubility Equations
Solubility equations describe the dynamic equilibrium established between a sparingly soluble ionic solid and its constituent ions when dissolved in a solvent, typically water. This equilibrium represents the point at which the maximum amount of solute has dissolved to form a saturated solution.
The Dissolution Equation for SrSO4
Strontium sulfate (SrSO4) is a sparingly soluble ionic compound. When it dissolves in water, it dissociates into its respective ions: strontium ions (Sr²⁺) and sulfate ions (SO₄²⁻). The balanced chemical equation representing this dissolution process is:
SrSO₄(s) ⇌ Sr²⁺(aq) + SO₄²⁻(aq)This equation shows that one mole of solid strontium sulfate dissociates to produce one mole of aqueous strontium ions and one mole of aqueous sulfate ions.
The Solubility Product (Ksp) Expression
The solubility product constant (Ksp) quantifies the extent to which an ionic compound dissolves in water at a specific temperature. For any sparingly soluble ionic compound, the Ksp expression is the product of the concentrations of its constituent ions, each raised to the power of its stoichiometric coefficient in the balanced dissolution equation.
For SrSO4, based on its dissolution equation SrSO₄(s) ⇌ Sr²⁺(aq) + SO₄²⁻(aq), the Ksp expression is:
Ksp = [Sr²⁺][SO₄²⁻]Relating Molar Solubility (S) to Ksp
Molar solubility (S) represents the concentration of the dissolved solid in a saturated solution, typically expressed in moles per liter (mol/L). For compounds like SrSO4 that dissociate into a 1:1 ratio of cations to anions, there is a direct relationship between Ksp and S.
If S is the molar solubility of SrSO4, then at equilibrium, the concentrations of the dissolved ions are:
[Sr²⁺] = S[SO₄²⁻] = S
Substituting these molar solubility values into the Ksp expression:
Ksp = (S)(S) = S²Therefore, the molar solubility (S) of SrSO4 can be calculated directly from its Ksp value using the equation:
S = √KspExample Calculation of SrSO4 Solubility
Given that the Ksp for SrSO4 is 2.8 × 10⁻⁷, we can calculate its molar solubility:
- Start with the relationship:
S = √Ksp - Substitute the given Ksp value:
S = √(2.8 × 10⁻⁷) - Calculate the molar solubility:
S ≈ 5.29 × 10⁻⁴ mol·L⁻¹
This calculation indicates that approximately 5.29 × 10⁻⁴ moles of SrSO4 can dissolve in one liter of water at the specified temperature (typically 25°C), forming a saturated solution.
Key Aspects of SrSO4 Solubility
The following table summarizes the key components of the solubility equation for SrSO4:
| Term | Definition/Equation | Value (for SrSO4) |
|---|---|---|
| Dissolution Equation | SrSO₄(s) ⇌ Sr²⁺(aq) + SO₄²⁻(aq) |
N/A |
| Ksp Expression | Ksp = [Sr²⁺][SO₄²⁻] |
N/A |
| Ksp Value | Solubility product constant | 2.8 × 10⁻⁷ |
| Molar Solubility (S) | S = √Ksp or [Sr²⁺] or [SO₄²⁻] |
5.29 × 10⁻⁴ mol·L⁻¹ |
The relatively low Ksp value for SrSO4 signifies that it is a sparingly soluble salt. Its solubility can be influenced by various factors, such as temperature changes or the presence of common ions (e.g., adding a source of Sr²⁺ or SO₄²⁻ ions would decrease its solubility due to the common ion effect).
