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Understanding Solubility Rules for Compounds

Aug 28, 2024

Solubility Rules for Ionic Compounds

Key Definitions

  • Soluble Compound: A compound that dissolves in water.
  • Insoluble Compound: A compound that does not dissolve in water.

General Solubility Rules

Always Soluble

  • Group 1 Metal Ions: Sodium (Na), Potassium (K), Lithium (Li), Rubidium (Rb).
  • Ammonium (NH₄⁺).
  • Polyatomic Ions:
    • Nitrate (NO₃⁻)
    • Acetate (CH₃COO⁻)

Halides (Chloride, Bromide, Iodide)

  • Generally Soluble.
  • Exceptions: Silver (Ag⁺), Lead (Pb²⁺), and Mercury (Hg₂²⁺).
    • Example: PbBr₂ is insoluble.

Sulfates (SO₄²⁻)

  • Generally Soluble.
  • Exceptions: Calcium (Ca²⁺), Barium (Ba²⁺), Strontium (Sr²⁺), and Lead (Pb²⁺).

Hydroxides (OH⁻)

  • Generally Insoluble.
  • Exceptions:
    • Soluble with Group 1 Metals (e.g., Na, K, Li) and Ammonium.
    • Soluble with some Group 2 Metals (Ca, Sr, Ba).
    • Magnesium Hydroxide (Mg(OH)₂) is only slightly soluble.

Sulfides, Carbonates, Phosphates, Chromates

  • Generally Insoluble.
  • Exceptions: Soluble with Group 1 Metals and Ammonium.

Applying Solubility Rules: Example Problems

Sodium Phosphate (Na₃PO₄)

  • Sodium (Na) is a Group 1 metal.
  • Result: Soluble (Aqueous).

Potassium Chloride (KCl)

  • Potassium (K) is a Group 1 metal.
  • Result: Soluble (Aqueous).

Silver Chloride (AgCl)

  • Chlorides are generally soluble, but silver (Ag⁺) is an exception.
  • Result: Insoluble (Solid).

Lead(II) Nitrate (Pb(NO₃)₂)

  • Nitrates are always soluble.
  • Result: Soluble (Aqueous).

Potassium Sulfate (K₂SO₄)

  • Potassium (K) is a Group 1 metal.
  • Result: Soluble (Aqueous).

Lead(II) Sulfate (PbSO₄)

  • Sulfates are generally soluble, but lead (Pb²⁺) is an exception.
  • Result: Insoluble (Solid).

Potassium Hydroxide (KOH)

  • Potassium (K) is a Group 1 metal.
  • Result: Soluble (Aqueous).

Barium Hydroxide (Ba(OH)₂)

  • Hydroxides are generally insoluble, but barium (Ba²⁺) is an exception.
  • Result: Soluble (Aqueous).

Magnesium Hydroxide (Mg(OH)₂)

  • Slightly soluble, generally treated as insoluble.
  • Result: Insoluble (Solid).

Lithium Carbonate (Li₂CO₃)

  • Lithium (Li) is a Group 1 alkali metal.
  • Result: Soluble (Aqueous).

Magnesium Phosphate (Mg₃(PO₄)₂)

  • Phosphates are generally insoluble.
  • Result: Insoluble (Solid).

Silver Nitrate (AgNO₃)

  • Nitrates are always soluble.
  • Result: Soluble (Aqueous).

Lead(II) Iodide (PbI₂)

  • Iodides are generally soluble, but lead (Pb²⁺) is an exception.
  • Result: Insoluble (Solid).

Now you know how to use the solubility rules to determine if a compound is soluble or insoluble in water. These guidelines will help you predict the solubility of ionic compounds effectively.

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