OXIDATION AND REDUCTION REACTIONS Originally, the term oxidation was used to describe the addition of oxygen to an element or a compound. a) Al b) Ba2+ c) Br 2 d) Ca e) Ga3+ f) H 2 g) H+ Now that you can assign proper oxidation numbers to the elements in substances, we can use changes in the oxidation numbers to identify oxidation and reduction reactions. Define each: Remember “Oil Rig”: Oxidation is loss (of e—)reduction is gain (of e—) a) Oxidation b) Reduction c) Oxidizing agent d) Reducing agent 2. • The initial combined Ag+ ions are in a +1 oxidation … Hydrogen –usually +1, except when bonded to Group I or Group II, when it forms hydrides, -1. 2CuO + C v 2Cu + CO 2 The gain or loss of oxygen is still a useful way of recognising some oxidation or reduction reactions, but with a knowledge of the structure of atoms, a rather H 3PO 2 + Cr 2O 7 2-→ H3PO 4 + Cr 3+ Basic Solution Cr 2O 7 2-+ C2H 4O → C 2H 4O 2 + Cr 3+ 4. The reverse is true for reduction There is no oxidation without a concurrent reduction 2. • The sum of the oxidation numbers of all atoms in a neutral compound is zero. Provided by the Academic Center for Excellence 3 Oxidation-Reduction Reactions • Oxygen in a compound is generally -2 (UNLESS in peroxides or with fluorine, in which case it is -1). Oxidation-Reduction Balancing Additional Practice Problems Acidic Solution 1. elemental metal were called "reduction" reactions, for example, the reduction of copper(II) oxide to copper by heating with charcoal (carbon). Likewise then, “reduction” applied to reactions where there was a “removal of oxygen”. A. Electrode Potential: is the tendency of a substance to accept electrons. Because of the presence of dioxygen in the atmosphere (~20%), many elements combine with it and this is the principal eg the oxidation state of copper in the copper(II) ion is referred to as +2 the more electrons removed from the atom or ion by oxidation, the higher its oxidation state eg Fe2+ - e-==> Fe3+, gives iron the oxidation state of +3 in the iron(III) ion (via a suitable oxidising agent). Zn + NO 3-→ Zn2+ + NH4 + 3. 1. Oxidation / Reduction Handout The original concept of “oxidation” applied to reactions where there was a “union with oxygen”. Use the Activity Series Chart. The oxygen was either furnished by elemental oxygen or by compounds containing oxygen. • Halogens (Group VII) in a compound are generally -1. Write half reactions for each of the following atoms or ions. but for more complex ions things are not so simple. Oxidation-Reduction in Soils. Worksheet 25 - Oxidation/Reduction Reactions Oxidation number rules: Elements have an oxidation number of 0 Group I and II – In addition to the elemental oxidation state of 0, Group I has an oxidation state of +1 and Group II has an oxidation state of +2. Example: Determine the oxidation number on S in Na Consider the following chemical equation: Zn(s) + 2HCl(aq) → Zn+2(aq) + 2Cl-­‐(aq) + H2(g) The oxidation number for elemental zinc is 0. Ag + NO 3-→ Ag+ + NO 2. Label each as oxidation or reduction. Oxidation‐Reduction Reactions • This can be more easily observed by writing the net ionic equation for the reaction: Cu (s) + 2 2+Ag+ (aq) 2 Ag (s) + Cu (aq) • The metallic Cu atoms are uncombined, so they are considered to have an oxidation number of zero. For example, Eho(v) O2 + 4H + + 4e- = 2H2O 1.23 Fe3+ + e-= Fe2+ 0.77 2H+ + 2e-= H2 0 (reference) Na+ + e- = Na - 2.71 TPSS 435. Or by compounds containing oxygen oxidation was used to describe the addition of oxygen an... 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