Chapter 20 OxidationReduction Reactions Anything in black letters

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

20. 1 – The Meaning of Oxidation and Reduction Original definitions, still useful… Oxidation Combining with oxygen Reduction Loss of oxygen Oxidation cannot occur without reduction.

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

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

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

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

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

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

20. 2 – Oxidation Numbers This section is really a review… Oxidation Number – charge on an ion. Elements & compounds have an oxidation # of zero. 0 0 +2 -1 Mg + Cl 2 Mg. Cl 2 Mg 0 Mg+2 + 2 e- Loss of e- = oxidation Cl 20 + 2 e- 2 Cl-1 Gain of e- = reduction

These should make sense…don’t write them all down! 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 +3. 2. The oxidation number of hydrogen in a compound is +1, except in metal hydrides, such as Na. H, 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 0. 5. For any neutral compound, the sum of the oxidation numbers of the atoms in the compound must equal 0. 6. For a polyatomic ion, the sum of the oxidation numbers must equal the ionic charge of the ion.

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 32– d. Cu 2 S

ASSIGNMENT: Chapter 20 Worksheet #1

20. 3 – Describing Redox Rxns Not covered…