Types of Chemical Reactions Redox Reactions: driven by the loss (oxidation) and gain (reduction) of electrons. Any species that does not change charge is called the spectator ion. – Synthesis Synthesis – Decomposition Decomposition – Single Replacement Single Replacement Ion Exchange Reaction: driven by the formation of an insoluble precipitate. The ions that remain dissolved throughout are the spectator ions. – Double Replacement Double Replacement

Decomposition A compound breaks down into its original elements. Na 2 O  2 Na + O 2 Same reaction, with charges added in: – Na 2 +1 O -2  2 Na 0 + O 2 0 O -2 is oxidized (loses electrons), is the reducing agent Na +1 is reduced (gains electrons), is the oxidizing agent Electrons are transferred from the O -2 to the Na +1. No spectator ions, there are only two elements here.

Single Replacement An element replaces the same type of element in a compound. Ca + 2 KCl  CaCl K Same reaction, with charges added in: – Ca K +1 Cl -1  Ca +2 Cl K 0 Ca 0 is oxidized (loses electrons), is the reducing agent K +1 is reduced (gains electrons), is the oxidizing agent Electrons are transferred from the Ca 0 to the K +1. Cl -1 is the spectator ion, since it’s charge doesn’t change.

Double Replacement The (+) ion of one compound bonds to the (-) ion of another compound to make an insoluble precipitate. The compounds must both be dissolved in water to break the ionic bonds first. NaCl (aq) + AgNO 3 (aq)  NaNO3 (aq) + AgCl (s) The Cl -1 and Ag +1 come together to make the insoluble precipitate, which looks like snow in the test tube. No species change charge, so this is not a redox reaction. Since the Na +1 and NO 3 -1 ions remain dissolved throughout the reaction, they are the spectator ions. How do identify the precipitate?

Identifying the Precipitate The precipitate is the compound that is insoluble. AgCl is a precipitate because Cl - is a halide. Halides are soluble, except when combined with Ag + and others.