Precipitation Reactions
Key Terms
To Know:
Soluble
Insoluble
Dissociation
Precipitate
Aqueous
Soluble: means that when it is placed in water, the substance dissociates into its component ions
For example, NaCl is soluble. When placed in water, it dissociates into Na+ and Cl-. When NaCl is placed in water, it is written as NaCl (aq) to indicate that it is mixed with water. Aqueous simply means that the compound is dissolved in water.
Consider the following soluble compounds:
| Compound | Cation Formed | Anion Formed |
| MgCl2 | Mg+2 | 2 Cl- |
| Ag(NO3) | Ag+ | (NO3)- |
| Fe(NO3)3 | Fe+3 | 3 (NO3)-1 |
Dissociation is the "splitting up" of an ionic compound. The cation separates from the anion. Remember to give the cation and anion charges. Also include the number of particles formed.
Example: Ca3N2 dissociates to become 3 Ca+2 and 2 N-3
When dissociating a polyatomic ion, like Ca3(PO4)2, the polyatomic ion doesn't dissociate from itself. Thus, this compound produces 3 Ca+2 and 2 (PO4)-3.
Click here to access Quia to practice dissociation of soluble compounds: http://www.quia.com/rr/133179.html
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Insoluble means that compound does NOT dissociates when it is placed in water. Instead, it simply remains as solid.
A precipitate is a compound that is formed in a chemical reaction that is insoluble. Essentially, precipitates and insoluble are interchangeable to a degree.
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