Рет қаралды 6,871
Precipitation Reactions occur when cations and anions of aqueous solutions combine to form an insoluble ionic solid, called aprecipitate. Whether or not such a reaction occurs can be determined by using the solubility rules for common ionic solids. Since not all aqueous reactions form precipitates, one must consult the solubility rules before determining the state of the products and writing a net ionic equation. Being able to predict these reactions allows scientists to calculate what ions are present in a solution, and allows industries to form chemicals by extracting certain elements from these reactions.
Solubility Rules : Whether or not a reaction will form a precipitate is dictated by the solubility rules. These rules provide us with the guidelines that tell which ions form solids and which remain in their ionic form in aqueous solution. The rules are to be followed from the top down, meaning that if something is insoluble (or soluble) due to rule 1, it has precedence over a higher-numbered rule, for example rule 4.
1. Salts formed with group 1 cations and NH4 + cations are soluble. There are some exceptions for certain Li+ salts.
2. Acetates (C2H3O2 - ), nitrates (NO3 - ), and perchlorates (ClO4 - ) are soluble.
3. Bromides, chlorides, and iodides are soluble
4. Sulfates (SO4 2- ) are soluble with the exception of sulfates formed with Ca2+, Sr2+, and Ba2+.
5. Salts containing silver, lead, and mercury (I) are insoluble.
6. Carbonates (CO3 2- ), phosphates (PO4 3- ), sulfides, oxides, and hydroxides (OH- ) are insoluble. Sulfides formed with group 2 cations and hydroxides formed with calcium, strontium, and barium are exceptions to the rule. If the rules state that an ion is soluble, then it will remain in its aqueous ion form. If an ion is insoluble based on the solubility rules, then it will form a solid with an ion from the other reactant in an equation. If all the ions in a reaction are shown to be soluble, then no precipitation reaction occurs.
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