Reactions in Which a Solid Forms
- The process of the formation of a solid is called precipitation
- The solid that forms is called a precipitate, and the reaction is known as a precipitation reaction
- In virtually every case when a solid containing ions dissolves in water, the ions separate and move around independently
- When each unit of a substance that dissolves in water produces separated ions, the substance is called a strong electrolyte
- When ionic compounds dissolve, the resulting solution contains the separated ions
- A solid compound must have a zero net charge
- Most ionic materials contain only two types of ions--one type of cation and one type of anion
- A soluble solid is a solid that readily dissolves in water; the solid "disappears" as the ions are dispersed in the water
- An insoluble solid and a slightly soluble solid are solids where such a tiny amount dissolves in water that it is undetectable with the naked eye
Rules of Solubility of Ionic Compounds:
- Most nitrate salts are soluble
- Most salts of Na, K, and NH4 are soluble
- Most chloride salts are soluble (Except AgCl, PbCl2, Hg2Cl2)
- Most sulfate salts are soluble (Except BaSO4, PbSO4, and CaSO4)
- Most hydroxide compounds are insoluble. (Except NaOH and KOH)
- Most sulfide, carbonate, and phosphate salts are insoluble (Exceptions in rule 2)
Definitions of the solubility rules: http://www.files.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html
Help in determining the Rules of Solubility: http://www.quia.com/rr/518467.html
How to Predict Precipitates When Solutions of Two Ionic Compounds Are Mixed:
- Write the reactants as they actually exist before any reaction occurs. Remember that when a salt dissolves, its ions separate
- Consider the various solids that could form. To do this, simply exchange the anions of the added salts.
- Use the solubility tules to decide whether a solid forms and, if so, to predict the identity of the solid