Solubility Rules Chart
Instantaneously predict precipitation reactions. Identify soluble and insoluble ionic compounds with our interactive guide.
Group 1 Ions (Li⁺, Na⁺, K⁺, etc.)
General Rule
All compounds containing Alkali Metal ions are soluble.
Exceptions
None
Ammonium (NH₄⁺)
General Rule
All compounds containing Ammonium ions are soluble.
Exceptions
None
Nitrate (NO₃⁻)
General Rule
All Nitrates are soluble.
Exceptions
None
Acetate (C₂H₃O₂⁻)
General Rule
All Acetates are soluble.
Exceptions
None
Chlorate (ClO₃⁻)
General Rule
All Chlorates are soluble.
Exceptions
None
Perchlorate (ClO₄⁻)
General Rule
All Perchlorates are soluble.
Exceptions
None
Chloride (Cl⁻)
General Rule
Most Chlorides are soluble.
Exceptions
Ag⁺, Pb²⁺, Hg₂²⁺
Bromide (Br⁻)
General Rule
Most Bromides are soluble.
Exceptions
Ag⁺, Pb²⁺, Hg₂²⁺
Iodide (I⁻)
General Rule
Most Iodides are soluble.
Exceptions
Ag⁺, Pb²⁺, Hg₂²⁺
Sulfate (SO₄²⁻)
General Rule
Most Sulfates are soluble.
Exceptions
Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Ag⁺, Hg₂²⁺
Hydroxide (OH⁻)
General Rule
Most Hydroxides are insoluble.
Exceptions
Group 1, NH₄⁺, Ca²⁺, Sr²⁺, Ba²⁺
Sulfide (S²⁻)
General Rule
Most Sulfides are insoluble.
Exceptions
Group 1, NH₄⁺, Ca²⁺, Sr²⁺, Ba²⁺
Carbonate (CO₃²⁻)
General Rule
Most Carbonates are insoluble.
Exceptions
Group 1, NH₄⁺
Phosphate (PO₄³⁻)
General Rule
Most Phosphates are insoluble.
Exceptions
Group 1, NH₄⁺
Chromate (CrO₄²⁻)
General Rule
Most Chromates are insoluble.
Exceptions
Group 1, NH₄⁺, Ca²⁺, Mg²⁺
Oxide (O²⁻)
General Rule
Most Oxides are insoluble.
Exceptions
Group 1, NH₄⁺, Ca²⁺, Sr²⁺, Ba²⁺
Mastering Solubility Rules
The Solubility Rules are a fundamental set of empirical guidelines used in chemistry to predict whether an ionic compound (commonly called a salt) will dissolve in water at room temperature. Understanding these rules is critical for predicting the products of double-displacement reactions, writing net ionic equations, and identifying unknown solutions in qualitative analysis.
Always Soluble
- ● Alkali Metals (Group 1): Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ are always soluble.
- ● Ammonium: All NH₄⁺ salts are soluble.
- ● Nitrates: All NO₃⁻ salts are soluble (No exceptions!).
- ● Acetates: CH₃COO⁻ salts are soluble.
Generally Insoluble
- ● Carbonates (CO₃²⁻): Insoluble (Except Group 1 & NH₄⁺).
- ● Phosphates (PO₄³⁻): Insoluble (Except Group 1 & NH₄⁺).
- ● Hydroxides (OH⁻): Insoluble (Except Group 1, Ca²⁺, Sr²⁺, Ba²⁺).
- ● Sulfides (S²⁻): Insoluble (Except Group 1, Group 2, NH₄⁺).
Why Things Dissolve
Dissolution is a battle between forces. For a salt to dissolve, the Ion-Dipole attraction (between water molecules and ions) must be strong enough to overcome the Lattice Energy (the ionic bonds holding the solid crystal together).
This explains why +1/-1 ions (like Na⁺ and Cl⁻) are often more soluble than highly charged +2/-2 ions (like Ca²⁺ and CO₃²⁻), which have much stronger lattice energies.
Net Ionic Equations
Solubility rules are the key to writing net ionic equations. Only substances that form a solid precipitate remain in the final equation.
// Molecular Equation
NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s)
// Net Ionic Equation
Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
Real-World Applications
- Water TreatmentPrecipitation is used to remove heavy metals (like Lead) from wastewater by adding sulfides or hydroxides.
- Medical ImagingBarium Sulfate (BaSO₄) is insoluble, making it safe to drink as a "Barium meal" for X-ray imaging of the gut.
- Kidney StonesCalcium Oxalate stones form because Calcium Oxalate is highly insoluble in the body's internal fluids.
Frequently Asked Questions
What are solubility rules used for?
Solubility rules are a set of empirical guidelines used to predict whether an ionic compound (salt) will dissolve in water or form a solid precipitate. They are essential for predicting the outcomes of double-displacement reactions.
Are all nitrates soluble?
Yes, essentially all nitrates (NO₃⁻) are soluble in water. There are no common exceptions, making this one of the most reliable rules in chemistry.
Is Silver Chloride (AgCl) soluble or insoluble?
Silver Chloride (AgCl) is insoluble. While most chlorides (Cl⁻) are soluble, Silver (Ag⁺), Lead(II) (Pb²⁺), and Mercury(I) (Hg₂²⁺) are heavy metal exceptions that form precipitates.
What does "slightly soluble" mean?
Slightly soluble means that only a very small amount of the substance dissolves in water (typically between 0.1g and 1g per 100mL). In many qualitative contexts, slightly soluble compounds are often treated as insoluble.
Why are Alkali Metal salts always soluble?
Alkali Metal ions (Group 1: Li⁺, Na⁺, K⁺, etc.) have a +1 charge and relatively large ionic radii, resulting in lower lattice energies that are easily overcome by hydration energy from water molecules.
What determines if a precipitate will form?
A precipitate forms if the product of a reaction involves a combination of ions that is classified as "insoluble" according to the solubility rules. If the attraction between the ions is stronger than their attraction to water, they will clump together as a solid.
How do I write a Net Ionic Equation?
To write a Net Ionic Equation: 1) Write the balanced molecular equation. 2) Dissociate all soluble strong electrolytes into ions. 3) Cross out "spectator ions" that appear unchanged on both sides. 4) The remaining ions forming the solid precipitate constitute the net ionic equation.
Are Hydroxides generally soluble?
No, most Hydroxides (OH⁻) are insoluble. The major exceptions are Alkali Metals (Group 1) and Ammonium (NH₄⁺). Heavy Alkaline Earth Metals (Ca²⁺, Sr²⁺, Ba²⁺) are slightly soluble.
What is the "CAST" mnemonic for solubility?
"CAST" is a popular mnemonic: C (Carbonates/Chromates - mostly insoluble), A (All Group 1 & Ammonium - soluble), S (Sulfides/Silver - mostly insoluble/exception), T (Thiosulfates/etc.). However, "NAG SAG" is more comprehensive: Nitrates, Acetates, Group 1, Sulfates, Ammonium, Group 17.
Why is PbCl₂ soluble in hot water?
Lead(II) Chloride (PbCl₂) is an interesting exception that is insoluble in cold water but becomes significantly more soluble in hot water due to the endothermic nature of its dissolution process.