Solubility Product Calculator

Calculate Ksp, predict precipitation, and determine molar solubility

Solubility Product Calculator

Solubility Product (Ksp): For MmAn ⇌ mM+ + nA-
Ksp = [M+]m[A-]n

Dissolution: MmAn ⇌ mM+ + nA-

Use scientific notation (e.g., 1.8e-10)

Ksp Values at 25°C:

• AgCl: 1.8×10⁻¹⁰
• BaSO₄: 1.1×10⁻¹⁰
• CaCO₃: 3.4×10⁻⁹
• PbI₂: 7.1×10⁻⁹
• Ag₂CrO₄: 1.1×10⁻¹²
• Ca₃(PO₄)₂: 2.1×10⁻³³

Understanding Ksp

The solubility product constant (Ksp) describes the equilibrium between a solid ionic compound and its dissolved ions in a saturated solution.

General Form:

MmAn(s) ⇌ mM+(aq) + nA-(aq)
Ksp = [M+]m[A-]n

Precipitation Rules

Qsp > Ksp

Supersaturated → Precipitate forms

Qsp = Ksp

Saturated → At equilibrium

Qsp < Ksp

Unsaturated → No precipitation

Applications

  • •Qualitative Analysis: Selective precipitation
  • •Water Treatment: Remove heavy metals
  • •Geochemistry: Mineral formation
  • •Medicine: Kidney stone prevention

🔗 Related Calculators

📐 Related Formulas

Example: AgCl Precipitation

Problem:

Will AgCl precipitate if 100 mL of 0.001 M AgNO₃ is mixed with 100 mL of 0.001 M NaCl? (Ksp of AgCl = 1.8×10⁻¹⁰)

Solution:

1. After mixing, volume = 200 mL

2. [Ag⁺] = (0.001 M)(100 mL)/(200 mL) = 5×10⁻⁴ M

3. [Cl⁻] = (0.001 M)(100 mL)/(200 mL) = 5×10⁻⁴ M

4. Qsp = [Ag⁺][Cl⁻] = (5×10⁻⁴)(5×10⁻⁴)

5. Qsp = 2.5×10⁻⁷

Qsp (2.5×10⁻⁷) > Ksp (1.8×10⁻¹⁰)

✓ Yes, AgCl will precipitate

Example: Molar Solubility

Problem:

Calculate the molar solubility of PbI₂ in pure water. (Ksp = 7.1×10⁻⁹)

Solution:

PbI₂(s) ⇌ Pb²⁺(aq) + 2I⁻(aq)

If s = molar solubility:

[Pb²⁺] = s, [I⁻] = 2s

Ksp = [Pb²⁺][I⁻]² = (s)(2s)² = 4s³

7.1×10⁻⁹ = 4s³

s³ = 1.775×10⁻⁹

s = 1.21×10⁻³ M

Molar solubility = 1.21×10⁻³ M

Or 1.21 millimoles per liter

Common Ksp Values at 25°C

CompoundFormulaKspSolubility
Silver chlorideAgCl1.8×10⁻¹⁰Very low
Barium sulfateBaSO₄1.1×10⁻¹⁰Very low
Calcium carbonateCaCO₃3.4×10⁻⁹Low
Lead(II) iodidePbI₂7.1×10⁻⁹Low
Silver chromateAg₂CrO₄1.1×10⁻¹²Very low
Iron(III) hydroxideFe(OH)₃2.8×10⁻³⁹Extremely low
Calcium phosphateCa₃(PO₄)₂2.1×10⁻³³Extremely low

Common Ion Effect

Concept:

Adding a common ion (an ion already present in the equilibrium) decreases the solubility of a sparingly soluble salt.

Example: AgCl is less soluble in 0.1 M NaCl than in pure water because of the added Cl⁻ ions.

Le Chatelier's Principle:

AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq)

Adding Cl⁻ shifts equilibrium left, reducing [Ag⁺] and thus the solubility of AgCl.

This principle is used in qualitative analysis to selectively precipitate ions.