[Skip to Content](https://www.sigmaaldrich.com#main-content) [![MilliporeSigma](https://www.sigmaaldrich.com/static/logos/purple/millipore_sigma.svg)](https://www.sigmaaldrich.com/US/en) Products Cart0 USEN Products ProductsApplicationsServicesResourcesSupport [Login / Register](https://www.sigmaaldrich.com/oidc-sign-in) [Order Lookup](https://www.sigmaaldrich.com/US/en/order-lookup) [Quick Order](https://www.sigmaaldrich.com/US/en/quick-order) Cart0 [Home](https://www.sigmaaldrich.com/US/en)[Solid State Synthesis](https://www.sigmaaldrich.com/US/en/applications/materials-science-and-engineering/solid-state-synthesis)Solubility Rules for Ionic Compounds # Solubility Rules for Ionic Compounds ## Solubility Chemistry [](https://www.sigmaaldrich.com)It’s important to know how chemicals will interact with one another in aqueous solutions. Some compounds or solutes will dissolve, others will yield a precipitate or solid, and a few react with water. You’ve probably run into solubility questions in your everyday life. Hot chocolate or flavored dry beverage mixes that don’t evenly dissolve in water would be examples of unwanted precipitates. Limescale or soap scum are __precipitates__ left behind when water with higher mineral content evaporates and introduces previously dissolved metal cations to carbonates or soap anions. Solubility is applicable to many laboratory processes and is also important in medicine. Some ions can be toxic when they separate in a solution but are helpful as part of a compound. A __saturated solution__ is one in which the maximum amount of solute has been dissolved. The opposite is a dilute solution; this solution can accept more solute. Pressure and temperature affect solubility. This page discusses the solubility of compounds in water at room temperature and standard pressure. A compound that is soluble in water forms an aqueous solution. ## Solubility Rules ### Which ions are soluble? IonsExcept Alkali metals (Group I) Na+, K+, etc.  Ammonium ions NH4+  Nitrates, acetates, chlorates, and perchlorate NO3-, C2H3O2-, ClO3-, ClO4-  Binary compounds of halogens (chloride, bromide, iodide, etc.) with metals Cl-, Br-, I-, etc.Fluoride Silver, lead, and mercury F-, Ag+, Pb2+\*, and Hg2+ \*Lead halides are soluble in hot water. All sulfates SO42-Barium, strontium, calcium, lead, silver, and mercury Ba2+, Sr2+, Ca2+, Pb2+, Ag+, and Hg2+ ### Which ions are slightly soluble? IonsExcept Sulfates of lead, silver, and mercury SO42- with Pb2+, Ag+, and Hg2+\*Lead sulfate is poorly soluble. Hydroxides of alkaline earth metals (Group II) OH- with Ca2+, Sr2+, etc.Barium Ba2+ ### Which ions are insoluble? IonsExcept Sulfides S2-Calcium, barium, strontium, magnesium, sodium, potassium, and ammonium Ca2+, Ba2+, Sr2+,  Mg2+, Na+, K+, and NH4+ Hydroxides OH-Alkali metals (Group I) and ammonium Na+, K+, etc. Al3+, NH4+ Carbonates, oxalates, chromates, and phosphates CO32-, C2O42-, CrO42-, and PO43-Alkali metals (Group I) and ammonium Na+, K+, etc. NH4+ \*Lithium phosphate is poorly soluble ## How to Use Solubility Rules 1. Identify the compound whose solubility you want to check. It can be helpful to write out the empirical formula so you can identify the ions that make up the compound. 2. Look up each ion in the solubility rules. Check the left-hand column for the general rule, and look in the right-hand column to make sure you noted any exceptions. 3. Alternatively, you can look up ions in the solubility chart. You might find this easier. Cations are listed across the top, and anions are listed vertically. Find the cell where your cation column and ion row meet to determine solubility of the resulting compound. Our solubility rules are not exhaustive. You may need to reference a [periodic table](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/chemistry-and-synthesis/organic-reaction-toolbox/periodic-table-of-elements-names) if you’re looking up less common compounds. ## Solubility Rules Chart [![Solubility Rules Chart](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/articles/materials-science-and-engineering/solid-state-synthesis/solubility-rules-chart.jpg "Solubility Rules Chart")](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/articles/materials-science-and-engineering/solid-state-synthesis/solubility-rules-chart-vector-mk.svg) Click for scalable vector graphic (SVG) ## Solubility Chart Download for Study and Classroom Use | | | | |------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [Downloadable PDF](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/documents/solubility-rules-chart-mk.pdf) | [Printable Image](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/articles/materials-science-and-engineering/solid-state-synthesis/large-solubility-rules-chart-mk.png) | [SVG (in-browser)](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/articles/materials-science-and-engineering/solid-state-synthesis/solubility-rules-chart-vector-mk.svg) | Our basic solubility chart is available free for download. Feel free to share it with friends, students, or teachers. Just make sure to link back to this page. Want to share some feedback about our study tools? Use the links above to contact us or leave a comment on one of our social media accounts. ## Solubility Definitions When discussing solubility, it’s useful to follow agreed standard definitions. The resources above present some general rules and loose definitions. The United States Pharmacopeia (USP), a nonprofit organization committed to establishing standards for medicines, food ingredients, dietary supplement products, and ingredients, has established the definitions below. These definitions are used by other major pharmacopeia organizations throughout the world and are often paired with exact measurements for more precise application needs. | | | |-----------------------|----------------------------------------------------| | Descriptive terms | Approximate volume of solvent in mL/g of substance | | Very soluble | less than 1 | | Easily soluble | from 1 to 10 | | Soluble | from 10 to 30 | | Sparingly soluble | from 30 to 100 | | Slightly soluble | from 100 to 1,000 | | Very slightly soluble | from 1,000 to 10,000 | | Practically insoluble | more than 10,000 | __Related Articles__ - [Solubility Table for Water at Temperature](https://www.sigmaaldrich.com/US/en/support/calculators-and-apps/solubility-table-compounds-water-temperature) - [Solvent Miscibility Table](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/purification/solvent-miscibility-table) - [VSEPR Chart | Valence Shell Electron Pair Repulsion Theory](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/chemistry-and-synthesis/organic-reaction-toolbox/vsepr-chart-valence-shell-electron-pair-repulsion-theory) - [Periodic Table of the Elements](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/chemistry-and-synthesis/organic-reaction-toolbox/periodic-table-of-elements-names) - [Solution Dilution Calculator](https://www.sigmaaldrich.com/US/en/support/calculators-and-apps/solution-dilution-calculator) - [Role of High Purity Metal Salts in Chemical Synthesis](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/chemistry-and-synthesis/ch-functionalization/role-of-high-purity-metal-salts-in-chemical-synthesis) - [Complex Hydrides: New Solid-state Conductors](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/materials-science-and-engineering/batteries-supercapacitors-and-fuel-cells/complex-hydrides) - [Mesoporous Oxides and Their Applications to Hydrogen Storage](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/materials-science-and-engineering/batteries-supercapacitors-and-fuel-cells/mesoporous-oxides) - [View More](https://www.sigmaaldrich.com/US/en/search/facet-search?focus=sitecontent&term=facet-search) Top __Sign In To Continue__ To continue reading please sign in or create an account. 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