Solubility Rules to Know for AP Chemistry

Understanding solubility rules is key in chemistry, helping predict how substances behave in water. These rules apply to various compounds, including alkali metals and ammonium, guiding reactions in AP Chemistry, Honors Chemistry, and Intro to Chemistry.

1. All alkali metal compounds are soluble.

   • Alkali metals include lithium (Li+), sodium (Na+), potassium (K+), rubidium (Rb+), cesium (Cs+), and francium (Fr+).
   • Their compounds dissolve easily in water, making them highly reactive in aqueous solutions.
   • This rule applies to all salts formed with alkali metals, regardless of the anion.

2. All ammonium compounds are soluble.

   • Ammonium (NH4+) is a positively charged polyatomic ion.
   • Compounds containing ammonium ions readily dissolve in water.
   • This includes a wide range of ammonium salts, such as ammonium chloride (NH4Cl).

3. All nitrates, acetates, and chlorates are soluble.

   • Nitrate (NO3-), acetate (C2H3O2-), and chlorate (ClO3-) ions form soluble compounds with most cations.
   • These compounds are commonly found in fertilizers and food preservatives.
   • Their solubility is consistent across various cations, making them reliable in reactions.

4. Most chlorides, bromides, and iodides are soluble, except those of Ag+, Pb2+, and Hg22+.

   • Chlorides (Cl-), bromides (Br-), and iodides (I-) are generally soluble in water.
   • Exceptions include silver (Ag+), lead (Pb2+), and mercury (Hg22+) salts, which are insoluble.
   • This rule is important for predicting the solubility of halide compounds in reactions.

5. Most sulfates are soluble, except those of Ba2+, Sr2+, Pb2+, and Ca2+.

   • Sulfate (SO4^2-) compounds are typically soluble in water.
   • Barium (Ba2+), strontium (Sr2+), lead (Pb2+), and calcium (Ca2+) sulfates are notable exceptions and are generally insoluble.
   • This rule is crucial for understanding the behavior of sulfate salts in various chemical processes.

6. Most hydroxides are insoluble, except those of alkali metals and Ba2+.

   • Hydroxides (OH-) are primarily insoluble in water, limiting their presence in aqueous solutions.
   • Alkali metal hydroxides and barium hydroxide (Ba(OH)2) are exceptions and dissolve readily.
   • This rule is significant for predicting the solubility of bases in reactions.

7. Most carbonates, phosphates, and sulfides are insoluble, except those of alkali metals and ammonium.

   • Carbonates (CO3^2-), phosphates (PO4^3-), and sulfides (S^2-) are generally insoluble in water.
   • Alkali metal and ammonium salts of these ions are exceptions and dissolve easily.
   • Understanding this rule helps in predicting the solubility of these compounds in various contexts.

8. Compounds containing polyatomic ions with alkali metals or ammonium are generally soluble.

   • Polyatomic ions, such as sulfate (SO4^2-) and nitrate (NO3-), form soluble compounds when paired with alkali metals or ammonium.
   • This rule reinforces the solubility of many common salts in chemistry.
   • It is essential for recognizing the behavior of complex ions in solution.