Redox Reactions. Chapter 18. + O 2 . Oxidation-Reduction (Redox) Reactions. “redox” reactions: rxns in which electrons are transferred from one species to another oxidation & reduction always occur simultaneously we use OXIDATION NUMBERS to keep track of electron transfers.
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1) the ox. state of any free (uncombined) element is zero.
2) The ox. state of an element in a simple ion is the charge of the ion.
Mg2+ oxidation of Mg is +2
(unless combined with a metal, then it has an ox. # of –1)
Ex: NaOH (H bonded to O) v. NaH (H bonded to Na)
4) the ox. # of fluorine is always –1.
5) the ox. # of oxygen is usually –2.
Why USUALLY? Not -2 when it’s in a peroxide, such as hydrogen peroxide:
6) in any neutral compound, the sum of the oxidation #’s = zero.
7) in a polyatomic ion, the sum of the oxidation #’s = the overall charge of the ion.
**use these rules to assign oxidation #’s; assign known #’s first, then fill in the #’s for the remaining elements:
MgCO3 MgO + CO2
Zn + CuSO4 ZnSO4 + Cu
NaCl + AgNO3 AgCl + NaNO3
CO2 + H2O C6H12O6 + O2