States of Matter Main

Characteristics of the Four States

Types of Solids

Crystal Structures

Solubilities of Solids

Intermolecular Forces in Liquids

Vapor Pressure

Gas Laws (Ideal and Non-Ideal)

Partial Pressures and Kp

Kinetic-Molecular Theory and Effusion

Solute Effects on Solvents

Solubility Products (Ksp)

Triple-Point Diagrams

Practice Problems


Solubilities of Solids

Some solids are extremely soluble--for example, table salt dissociates fully in water, becoming Na+ and Cl- ions floating about in water instead of a crystalline solid. Other solids, like AgCl, silver chloride, are barely soluble at all. How can we predict the solubility of a given solid, when it sounds like similar solids have such different solubility characteristics.

There are some general guidelines for solubilty, and while there will always be excepts, we can at least get some idea of which compounds will be soluble.

Negative Ion Positive Ion Solubility
Almost all Alkali metal ions, hydrogen ion (H+), ammonium ion (NH4+) High (very soluble)
Nitrate ion (NO3-) Almost all High (very soluble)
Acetate ion (CH3COO-) Almost all High (very soluble)
Chloride, Bromide, Iodide (Cl-, Br-, I-) Ag+, Pb2+, Hg22+, Cu+, Tl+ Low (not soluble)
Chloride, Bromide, Iodide (Cl-, Br-, I-) All others High (very soluble)
Sulfate (SO42-) Ca2+, Sr2+, Ba2+, Pb2+, Ra2+ Low (not soluble)
Sulfate (SO42-) All others High (very soluble)
Sulfide (S2-) Alkali metal ions, H+, NH4+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Ra2+ High (very soluble)
Sulfide (S2-) All others Low (not soluble)
Hydroxide (OH-) Alkali metal ions, H+, NH4+, Sr2+, Ba2+, Ra2+, Tl+ High (very soluble)
Hydroxide (OH-) All others Low (not soluble)
Phosphate, Carbonate, Sulfite (PO43-, CO32-, SO32-) Alkali metal ions, H+, NH4+ High (very soluble)
Phosphate, Carbonate, Sulfite (PO43-, CO32-, SO32-) All others Low (not soluble)

This table is very useful, especially when working with Le Chatlier's principle, because we can use insoluble anion-cation pairs to precipitate products of a reaction and drive the reaction to the right. For instance, if a product of some reaction is the chloride ion, we know that introducing the lead ion (Pb2+) will cause the chloride to precipitate. Since the concentration of the products is low, the equilibrium law will generate more products to replace it.

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