Solubility Rules
Core Concept
Solubility refers to the ability of a substance, known as the solute, to dissociate in another substance, known as the solvent, to form a homogeneous mixture called a solution.
Memorize the "Big Five": Start by memorizing that $NAG$ $SAG$ (Nitrates, Acetates, Group 1, Sulfates, Ammonium, Group 17) are usually soluble to cover most cases.
Watch for "The Heavy Three": Remember that Silver ($Ag^+$), Mercury ($Hg_2^{2+}$), and Lead ($Pb^{2+}$) frequently turn otherwise soluble halides and sulfates into precipitates.
Check the State Symbols: When writing equations, always label soluble compounds as $(aq)$ and insoluble precipitates as $(s)$.
Use a Process of Elimination: If you see a Group 1 metal (like $Na^+$ or $K^+$) in a formula, you can immediately stop checking rules—it is soluble.
Test Yourself
Practice Problems & Worked Out Examples 🔒
Overview
Solubility refers to the ability of a substance, known as the solute, to dissociate in another substance, known as the solvent, to form a homogeneous mixture called a solution.
The solubility of a substance is determined by the interactions between the solute particles and the solvent particles. These interactions can be influenced by factors such as the nature of the solute and solvent, temperature, pressure, and the presence of other solutes or additives.
Solubility can be reported in various units, such as grams per liter (g/L), moles per liter (mol/L or M), or as a percentage.
Substances can be classified into three categories based on their solubility:
Soluble: A substance is considered soluble if it readily dissolves in a given solvent to form a solution. Examples include table salt (sodium chloride) dissolving in water.
Insoluble: A substance is considered insoluble if it does not dissolve appreciably in a given solvent. Examples include sand in water or oil.
Partially soluble: Some substances exhibit partial solubility, where they dissolve to a limited extent in a solvent. This can vary depending on the conditions and the amount of solute and solvent present.
The solubility can vary with temperature and pressure. In general, as temperature increases, the solubility of solid solutes in liquids tends to increase. However, for gases dissolved in liquids, the solubility typically decreases with increasing temperature.
Solubility Rules
Soluble:
Salts of Group 1 elements (Li+, Na+, K+, Rb+, Cs+): Almost all salts of these alkali metals are soluble in water.
Salts of the Ammonium Ion (NH₄⁺): Ammonium salts generally behave similarly to alkali metal salts and are soluble in water.expand_more
Nitrates (NO₃⁻): Salts containing the nitrate ion are soluble in water.expand_more
Most Chlorides (Cl⁻), Bromides (Br⁻), and Iodides (I⁻): Salts containing these halides are generally soluble with a few exceptions.expand_more These exceptions include:
Silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI)
Lead (II) chloride (PbCl₂), lead (II) bromide (PbBr₂)exclamation
Mercury (I) chloride (Hg₂Cl₂)
Slightly Soluble:
Calcium Hydroxide (Ca(OH)₂): This compound has low solubility in water, but a small amount will dissolve, creating a slightly basic solution (limewater).
Insoluble:
Most Sulfates (SO₄²⁻): Exceptions include salts of Group 1 elements (Li₂SO₄, Na₂SO₄, K₂SO₄, etc.), ammonium sulfate ((NH₄)₂SO₄), and some other specific sulfates.
Most Carbonates (CO₃²⁻) and Phosphates (PO₄³⁻): Exceptions include salts of Group 1 elements and the ammonium ion.
Most Hydroxides (OH⁻): Exceptions include hydroxides of Group 1 elements, calcium hydroxide (Ca(OH)₂), and barium hydroxide (Ba(OH)₂). These have varying degrees of solubility.
Sulfides (S²⁻): Most sulfides are insoluble in water. Exceptions include salts of Group 1 elements and Group 2 elements (magnesium, calcium, strontium, barium).
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