Chapter 20 Oxidation-Reduction Reactions Anything in black letters = write it in your notes (‘knowts’)

20.1 – The Meaning of Oxidation and Reduction Combining with oxygen Reduction Loss of oxygen Oxidation cannot occur without reduction. Oxidation Original definitions, still useful…

Combining with oxygen Reduction Loss of oxygen Oxidation CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O(g) 4Fe(s) + 3O 2 (g) → 2Fe 2 O 3 (s) 2Fe 2 O 3 (s) + 3C(s) → 4Fe(s) + 3CO 2 (g) Circle the substance that is being oxidized

Loss of electrons Reduction Gain of electrons Oxidation Modern definitions, more useful…

Helpful acronym… ‘LEO the lion says GER’ ger Loss of Electrons is Oxidation Gain of Electrons is Reduction

Mg(s) + S(s) MgS(s) heat Oxidation Loss of electrons Reduction Gain of electrons Mg is oxidized because it lost 2 e - A substance can be oxidized without reacting with oxygen.

Oxidizing Agent – causes another substance to be oxidized. Reducing Agent – causes another substance to be reduced. 2C + O 2  2CO Reducing Agent Oxidizing Agent Carbon is oxidized, oxygen is reduced. The oxidizing agent will always be reduced

2AgNO 3 (aq) + Cu(s) → Cu(NO 3 ) 2 (aq) + 2Ag(s) Circle the oxidizing agent

20.2 – Oxidation Numbers This section is really a review… Oxidation Number – charge on an ion. Elements & compounds have an oxidation # of zero. Mg + Cl 2  MgCl Mg 0  Mg e - Cl e -  2Cl -1 Loss of e - = oxidation Gain of e - = reduction

Rules for Assigning Oxidation Numbers 1. The oxidation number of a monatomic ion is equal in magnitude and sign to its ionic charge. For example, the oxidation number of the bromide ion (Br 1– ) is –1; that of the Fe 3+ ion is The oxidation number of hydrogen in a compound is +1, except in metal hydrides, such as NaH, where it is –1. 3. The oxidation number of oxygen in a compound is –2, except in peroxides, such as H 2 O 2, where it is –1, and in compounds with the more electronegative fluorine, where it is positive. 4. The oxidation number of an atom in uncombined (elemental) form is 0. For example, the oxidation number of the potassium atoms in potassium metal (K) or of the nitrogen atoms in nitrogen gas (N 2 ) is For any neutral compound, the sum of the oxidation numbers of the atoms in the compound must equal For a polyatomic ion, the sum of the oxidation numbers must equal the ionic charge of the ion. These should make sense…don’t write them all down!

What is the oxidation number of each kind of atom in the following ions and compounds? a.SO 2 b. Na 2 SO 4 c. CO 3 2– d. Cu 2 S

ASSIGNMENT: Chapter 20 Worksheet #1

20.3 – Describing Redox Rxns Not covered…