Solubility
Solubility is the maximum amount of a substance (solute) that can dissolve in a given quantity of solvent at a specified temperature and pressure to form a homogeneous solution. Beyond this limit, the solution is saturated and excess solute remains undissolved. Solubility depends on the chemical nature of solute and solvent, temperature (usually increases for solids in liquids, decreases for gases), and pressure (significant only for gases, governed by Henry's Law).
Key Formula
Ksp = [A^m+]^n × [B^n-]^m (for sparingly soluble salt A_n B_m)
LaTeX: K_{sp} = [\text{A}^{m+}]^{n}[\text{B}^{n-}]^{m}
| Symbol | Meaning | Unit |
|---|---|---|
| K_sp | Solubility product constant | dimensionless (concentration units implied) |
| [A^m+] | Molar concentration of cation A at saturation | mol/L |
| [B^n-] | Molar concentration of anion B at saturation | mol/L |
| n, m | Stoichiometric coefficients from dissociation equation | dimensionless |
Worked Example
Problem
The K_sp of AgCl at 25 °C is 1.8 × 10⁻¹⁰. Calculate the molar solubility (s) of AgCl in pure water.
Solution
Step 1: Write the dissolution equation: AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq). Step 2: Set up ICE table: [Ag⁺] = s, [Cl⁻] = s at equilibrium. Step 3: Apply K_sp: K_sp = [Ag⁺][Cl⁻] = s × s = s². Step 4: Solve: s² = 1.8 × 10⁻¹⁰, so s = √(1.8 × 10⁻¹⁰) = 1.34 × 10⁻⁵ mol/L.
Answer
Molar solubility of AgCl = 1.34 × 10⁻⁵ mol/L (≈ 0.00192 g/L)
Solubility of Common Substances in Water at 25 °C
| Substance | Formula | Solubility (g/100 mL) | Classification |
|---|---|---|---|
| Sodium chloride | NaCl | 35.9 | Highly soluble |
| Sugar (sucrose) | C₁₂H₂₂O₁₁ | 200 | Highly soluble |
| Calcium carbonate | CaCO₃ | 0.0013 | Sparingly soluble |
| Silver chloride | AgCl | 0.000192 | Insoluble (K_sp governed) |
| Oxygen gas | O₂ | 0.0043 | Slightly soluble (gas) |
| Sand (SiO₂) | SiO₂ | ~0.000006 | Practically insoluble |
Interactive Tools
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Related Terms
Henry's Law
Henry's Law states that the amount of a gas dissolved in a liquid at constant temperature is directly proportional to the partial pressure of that gas above the liquid. It applies to dilute solutions of gases that do not react chemically with the solvent. Henry's Law explains why carbonated beverages fizz when opened (pressure release), and is critical in understanding oxygen transport in blood, gas exchange in lungs, and environmental fate of volatile compounds.
Molarity
Molarity (M) is the most common measure of solution concentration, defined as the number of moles of solute dissolved per litre of solution. It is temperature-dependent because liquid volumes change with temperature. Molarity is widely used in titrations, reaction stoichiometry involving solutions, and the preparation of standard laboratory solutions.
Mole Fraction
Mole fraction (χ) is a dimensionless concentration unit expressing the ratio of the moles of one component to the total moles of all components in a mixture. The sum of all mole fractions in a mixture always equals exactly 1. Mole fraction is used in Raoult's law, Dalton's law of partial pressures, and chemical thermodynamics because it is independent of temperature and pressure.
From Latin "solubilis" (able to be loosened or dissolved), from "solvere" (to loosen, dissolve). The scientific concept was formalised in the 18th and 19th centuries alongside the development of analytical and physical chemistry.