Solubility Rules Reference Cheat Sheet

A printable reference covering solubility rules, precipitates, net ionic equations, spectator ions, and common soluble and insoluble salts for grades 9-12.

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Solubility rules help students predict whether an ionic compound dissolves in water or forms a solid precipitate. This cheat sheet covers the most common classroom rules for nitrates, alkali metal salts, ammonium salts, halides, sulfates, carbonates, phosphates, hydroxides, and sulfides. Students need these rules to write balanced double replacement reactions, identify precipitates, and simplify complete ionic equations into net ionic equations. The core idea is that aqueous ionic compounds separate into ions, while insoluble compounds remain together as solids. A precipitation reaction occurs when ions in solution combine to form an insoluble product, such as $\text{Ag}^{+}(aq) + \text{Cl}^{-}(aq) \rightarrow \text{AgCl}(s)$ . Strong solubility rules, such as all nitrates being soluble, are applied before exception rules. Net ionic equations include only the ions and compounds that actually change during the reaction.

Key Facts

All Group $1$ metal salts and ammonium salts are soluble, so compounds containing $\text{Li}^{+}$ , $\text{Na}^{+}$ , $\text{K}^{+}$ , or $\text{NH}_{4}^{+}$ are usually written as aqueous.
All nitrate, acetate, chlorate, and perchlorate salts are soluble, so salts containing $\text{NO}_{3}^{-}$ , $\text{C}_{2}\text{H}_{3}\text{O}_{2}^{-}$ , $\text{ClO}_{3}^{-}$ , or $\text{ClO}_{4}^{-}$ are usually aqueous.
Most chloride, bromide, and iodide salts are soluble, but salts with $\text{Ag}^{+}$ , $\text{Pb}^{2+}$ , or $\text{Hg}_{2}^{2+}$ are insoluble or only slightly soluble.
Most sulfate salts are soluble, but $\text{BaSO}_{4}$ , $\text{SrSO}_{4}$ , $\text{PbSO}_{4}$ , and often $\text{CaSO}_{4}$ are insoluble or only slightly soluble.
Most carbonate and phosphate salts are insoluble, except those containing Group $1$ ions or $\text{NH}_{4}^{+}$ .
Most hydroxide salts are insoluble, except Group $1$ hydroxides, while $\text{Ca(OH)}_{2}$ , $\text{Sr(OH)}_{2}$ , and $\text{Ba(OH)}_{2}$ are more soluble than most hydroxides.
A precipitate forms when two aqueous ionic solutions produce an insoluble product, such as $\text{Ba}^{2+}(aq) + \text{SO}_{4}^{2-}(aq) \rightarrow \text{BaSO}_{4}(s)$ .
Spectator ions appear unchanged on both sides of a complete ionic equation and are removed to write the net ionic equation.

Vocabulary

Solubility: Solubility is the ability of a substance to dissolve in a solvent, usually water in chemistry class reactions.
Aqueous: Aqueous means dissolved in water and is shown with the state symbol $(aq)$ .
Precipitate: A precipitate is an insoluble solid that forms when ions in solution combine.
Spectator ion: A spectator ion is an ion that stays dissolved and unchanged during a reaction.
Net ionic equation: A net ionic equation shows only the reacting ions and the precipitate, gas, or weak electrolyte that forms.
Double replacement reaction: A double replacement reaction is a reaction in which two ionic compounds exchange ions, often written as $\text{AB} + \text{CD} \rightarrow \text{AD} + \text{CB}$ .

Common Mistakes to Avoid

Writing every product as aqueous is wrong because solubility rules determine whether each product is $(aq)$ or $(s)$ .
Forgetting exception ions is wrong because rules such as most chlorides are soluble do not apply to compounds like $\text{AgCl}$ and $\text{PbCl}_{2}$ .
Canceling solids as spectator ions is wrong because a precipitate such as $\text{BaSO}_{4}(s)$ does not separate into ions in the net ionic equation.
Balancing the molecular equation after writing ions is risky because charge and atom balance should be correct before splitting soluble ionic compounds.
Splitting insoluble compounds into ions is wrong because insoluble substances remain together, such as $\text{AgCl}(s)$ rather than $\text{Ag}^{+}(aq) + \text{Cl}^{-}(aq)$ .

Practice Questions

1 Predict whether a precipitate forms when $\text{AgNO}_{3}(aq)$ is mixed with $\text{NaCl}(aq)$ , and name the precipitate if one forms.
2 Write the balanced molecular equation and net ionic equation for $\text{BaCl}_{2}(aq) + \text{Na}_{2}\text{SO}_{4}(aq)$ .
3 Classify each compound as soluble or insoluble in water: $\text{K}_{2}\text{CO}_{3}$ , $\text{CaCO}_{3}$ , $\text{NH}_{4}\text{Cl}$ , and $\text{PbI}_{2}$ .
4 Explain why $\text{Na}^{+}$ and $\text{NO}_{3}^{-}$ are often spectator ions in precipitation reactions.

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