University:
University of North Carolina at Charlotte
Course:
CHEM 1251 | General Chemistry I
Academic year:

2024
Views:

159

Pages:

4
Author:

Kamila P.

CHAPTER 9 OXIDATION-REDUCTION REDUCTION (chemical reactions in which electrons transfer from one reactant to the other) A few examples of applications of redox reactions: Biology Electric power Forensics OXIDATION STATES (AKA OXIDATION NUMBER) Oxidation state/number: the "charge" of an atom in a compound if all shared (bonding) electrons were "owned" by the more electronegative atom. Following rules come in ORDER OF IMPORTANCE: Free elements always have an oxidation state of 0. Na, O₂, N₂ = 0 Monatomic ions always have an oxidation state equal to their charge. Na⁺ = +1, O²⁻ = -2 The sum of the oxidation states of all the atoms in a compound is 0. The sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion. Some elements have the same oxidation number when part of a compound. You are expected to know these oxidation numbers: Group 1A metal: +1 Group 2A metal: +2 Hydrogen: +1 (except when bonded with a more electronegative element, then it's -1) Oxygen: -2 (except in peroxides, where it's -1, or superoxides, where it's -1/2) Halogens (non-F): -1 Example: C₂H₅OH 2x + 6(1) + 1(-2) + 1(-2) = 0 2x + 6 - 2 - 2 = 0 2x + 2 = 0 x = -1 Problem: I₂: 0 (by itself, neutral = 0) Sulfide ion: S²⁻ = -2 Calcium Bromide: CaBr₂ → Ca²⁺ and Br⁻ → Ca = +2 and Br = -1 Sulfate ion: SO₄²⁻ → O = -2, x + 4(-2) = -2 → x = +6 CaHe (molecular compound): H = +1, 2x + 6(1) = 0 → 2x = -6 → x = -3 Carbon monoxide: CO → C = x, O = -2 → x + (-2) = 0 → x = +2 Carbon dioxide: CO₂ → C = x, O = -2 → x + (-2)(-2) = 0 → x = +4 REDOX = REDUCTION and OXIDATION 2Na(s) + Cl₂(g) → 2NaCl(s) Electrons are transferred from sodium to chlorine, forming sodium chloride. Sodium is oxidized, and chlorine is reduced. In the reaction of sodium metal and chlorine gas to produce sodium chloride: Which atom is oxidized? Na Which atom is reduced? Cl Consider the reaction: H₂(g) + Cl₂(g) → 2HCl(g): Which atom is oxidized? H Which atom is reduced? Cl REDOX REACTION Oxidation and reduction must occur simultaneously. If one atom loses electrons, another atom must take them. N₂(g) + 3H₂(g) → 2NH₃(g) If nitrogen is gaining electrons, it is being reduced. If hydrogen is losing electrons, it is being oxidized. LEO GER! Lose Electrons, Oxidation Gain Electrons, Reduction END EXAM 4 In this reaction: Sn(s) + 4HNO₃(aq) → SnO₂(s) + 4NO₂ + 2H₂O(g) Which element is oxidized? Sn Which element is reduced? N IDENTIFYING REDOX REACTIONS: Determine whether or not each reaction is a redox reaction. For redox reactions, identify which element is oxidized and which element is reduced. A. 2Al(s) + 3Sn⁴⁺(aq) → 2Al³⁺(aq) + 3Sn²⁺(s) * Oxidized: Al * Reduced: Sn B. Pb(NO₃)₂(aq) + 2Li(aq) → PbCl₂(s) + 2LiNO₃(aq) * Not a redox reaction