Solubility Rules Lookup
Search a compound or ion family and see the solubility rule, exception and precipitation clue.
What can you search?
| Search | Example input | What the tool checks |
|---|---|---|
| Specific compound | AgCl, BaSO4, NaNO3 | Common rule plus exception |
| Ion family | sulfate, carbonate, hydroxide | General soluble or insoluble pattern |
| Exception name | silver chloride, barium sulfate | High-priority exception before broad rule |
| Precipitation clue | AgNO3 + NaCl products | Whether the new salt is likely solid |
Solubility rule ladder
Worked examples
NaNO3: sodium is Group 1 and nitrate is generally soluble, so the salt is soluble.
AgCl: chlorides are usually soluble, but Ag+ is an exception, so AgCl is likely insoluble.
BaSO4: sulfates are usually soluble, but Ba2+ is a standard exception, so BaSO4 is likely insoluble.
Na2CO3: carbonates are usually insoluble, but sodium is Group 1, so sodium carbonate is soluble.
Using rules in precipitation reactions
For a double-replacement reaction, swap ions to write the possible products, then apply solubility rules to each product. If one product is insoluble, that solid is the precipitate and usually appears in the net ionic equation.
How the visual ladder helps
The rule ladder highlights the matched family and keeps exceptions visible. This helps avoid the most common error: applying a broad rule before checking whether the compound is one of the listed exceptions.
Where this lookup is useful
- Predicting precipitates in double-replacement reactions.
- Writing complete ionic and net ionic equations.
- Checking whether a salt should be labeled aq or s.
- Reviewing polyatomic ion families such as nitrate, sulfate, carbonate and phosphate.
- Connecting reaction classification with actual observable products.
Common mistakes
- Forgetting that Group 1 and ammonium exceptions can make many salts soluble.
- Calling all sulfates soluble and missing BaSO4, PbSO4 or SrSO4.
- Confusing sulfate with sulfide; they follow different rules.
- Using solubility rules without first writing correct product formulas and charges.
Result checking
If your prediction says a precipitate forms, confirm that the ions came from soluble reactants and that the product formula is charge-balanced. For borderline cases such as CaSO4, remember that concentration and Ksp can matter.
Related Chemistry Tools
FAQs
Are ionic compounds soluble in water?
Some are, some aren't — solubility depends on the balance between lattice energy (which holds ions in the solid) and hydration energy (which stabilizes ions in solution). Polar water molecules orient their O end toward cations and their H end toward anions; if the resulting ion-dipole attractions overcome the lattice energy, the salt dissolves. Reliable groupings: all alkali-metal (Group 1) and ammonium salts are soluble; all nitrates, acetates, and chlorates are soluble; most chlorides, bromides, and iodides are soluble (Ag+, Pb2+, and Hg2^2+ are exceptions); most carbonates, phosphates, sulfides, and hydroxides are insoluble unless paired with Group 1 or NH4+. Examples: NaCl, KNO3, and CuSO4 dissolve readily; AgCl, BaSO4, CaCO3, and Mg(OH)2 do not.
What are the solubility rules?
A working set of rules for predicting whether an ionic compound dissolves in water: (1) All Group 1 (Li+, Na+, K+, Rb+, Cs+) salts are soluble. (2) All NH4+ salts are soluble. (3) All nitrates (NO3-), acetates (CH3COO-), and chlorates (ClO3-) are soluble. (4) Chlorides, bromides, and iodides are soluble except for Ag+, Pb2+, and Hg2^2+ — and PbCl2 is moderately soluble in hot water. (5) Sulfates are soluble except for Ba2+, Sr2+, Pb2+; CaSO4 is only slightly soluble. (6) Carbonates, phosphates, and sulfides are insoluble except for Group 1 cations and NH4+. (7) Hydroxides are insoluble except for Group 1 cations, NH4+, Ba(OH)2 (soluble), Sr(OH)2 (soluble), and Ca(OH)2 (slightly soluble).
How to know if a compound is soluble in water?
Apply the solubility rules in order: identify the cation and anion, then check whether either is in a category with a clear rule. Step 1 — Cation: if the cation is from Group 1 (Li+, Na+, K+, Rb+, Cs+) or is NH4+, the salt is soluble regardless of the anion. Step 2 — Anion: if the anion is NO3-, CH3COO-, or ClO3-, the salt is soluble regardless of the cation. Step 3 — Halides: Cl-, Br-, I- are soluble except with Ag+, Pb2+, Hg2^2+. Step 4 — Sulfates: SO4^2- is soluble except with Ba2+, Sr2+, Pb2+; slightly soluble with Ca2+. Step 5 — Insoluble groups: CO3^2-, PO4^3-, S^2-, OH- are generally insoluble unless paired with a Step 1 cation. Worked check: NaCl — Group 1 cation, soluble; AgCl — silver halide exception, insoluble; BaSO4 — sulfate exception, insoluble; K3PO4 — Group 1 cation, soluble.
Are carbonates soluble?
Most carbonates are insoluble. The exceptions are alkali-metal carbonates (Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs2CO3) and ammonium carbonate ((NH4)2CO3). Common insoluble carbonates: CaCO3 (limestone, marble, eggshells), MgCO3, BaCO3, FeCO3, PbCO3, ZnCO3, CuCO3. Test for a carbonate: add dilute HCl — effervescence of CO2 confirms a carbonate. CaCO3 + 2HCl → CaCl2 + H2O + CO2. Practical context: hard water owes its temporary hardness to dissolved Ca(HCO3)2 (the bicarbonate is more soluble than the carbonate); on heating, that bicarbonate decomposes and CaCO3 scale precipitates inside kettles and pipes.
Are hydroxides soluble?
Most hydroxides are insoluble. The reliably soluble ones are the Group 1 hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) and Ba(OH)2; Sr(OH)2 is also soluble. Ca(OH)2 is slightly soluble (about 1.6 g/L at 20 °C — that is what 'lime water' is). Insoluble hydroxides used in qualitative analysis include Mg(OH)2 (white), Cu(OH)2 (pale blue), Fe(OH)2 (green), Fe(OH)3 (red-brown), Al(OH)3 (gelatinous white), and Zn(OH)2 (white). Solubility increases down Group 2: Mg(OH)2 < Ca(OH)2 < Sr(OH)2 < Ba(OH)2. Typical precipitation reactions: FeCl3 + 3NaOH → Fe(OH)3↓ + 3NaCl; CuSO4 + 2NaOH → Cu(OH)2↓ + Na2SO4.
Are phosphates soluble?
Most phosphates are insoluble. The soluble ones are Group 1 phosphates (Na3PO4, K3PO4, Li3PO4) and ammonium phosphate ((NH4)3PO4). Common insoluble phosphates: Ca3(PO4)2 (the inorganic component of bone), Mg3(PO4)2, FePO4, AlPO4. Hydroxyapatite, Ca5(PO4)3OH, is the dominant mineral in tooth enamel. Industrial relevance: phosphate rock is mostly insoluble Ca3(PO4)2, which is converted into the water-soluble single superphosphate fertilizer by reaction with sulfuric acid: Ca3(PO4)2 + 2H2SO4 → Ca(H2PO4)2 + 2CaSO4.
Is Ag soluble?
Silver metal does not dissolve in water, but it does react with oxidizing acids. With concentrated HNO3: 3Ag + 4HNO3 → 3AgNO3 + NO + 2H2O. With hot concentrated H2SO4: 2Ag + 2H2SO4 → Ag2SO4 + SO2 + 2H2O. In the cyanide leaching used to extract silver: 4Ag + 8CN- + O2 + 2H2O → 4[Ag(CN)2]- + 4OH-. For silver compounds, the solubility rule is that most Ag+ salts are insoluble — AgCl, AgBr, AgI, Ag2S, Ag2CO3, and Ag2CrO4 are all insoluble. The notable soluble silver salts are AgNO3, AgF, and AgClO4.
Is AgOH soluble in water?
AgOH is insoluble in water and is also chemically unstable, so it cannot be isolated as a pure compound under normal conditions. When NaOH is added to AgNO3, an unstable white AgOH forms briefly and immediately dehydrates to brown Ag2O: 2AgOH → Ag2O + H2O. The Ksp of AgOH is roughly 2 × 10^-8, putting it firmly in the insoluble category. Practical observation: adding NaOH to AgNO3 yields the brown precipitate of Ag2O, written overall as 2AgNO3 + 2NaOH → Ag2O↓ + 2NaNO3 + H2O.
Is Mg soluble?
Magnesium metal is not soluble in pure water at room temperature; the surface forms a thin Mg(OH)2 layer that slows further reaction. With steam it reacts much faster: Mg + H2O(g) → MgO + H2. With dilute acids it reacts vigorously: Mg + 2HCl → MgCl2 + H2. Solubility of magnesium compounds follows the usual ionic rules. Soluble: MgCl2, Mg(NO3)2, MgSO4 (Epsom salt is MgSO4·7H2O), Mg(CH3COO)2, MgBr2, MgI2. Insoluble: Mg(OH)2 (the active ingredient in milk of magnesia), MgCO3, Mg3(PO4)2, MgF2. MgF2 is unusual because most fluorides are soluble; the small Mg2+ and small F- combine to give a very high lattice energy.