9.1 Oxidation and Reduction Part 1 IB Chemistry SL Mrs. Page 1 Photo from:

Understandings: (What should I know)  Oxidation and reduction can be considered in terms of oxygen gain/hydrogen loss, electron transfer or change in oxidation number.  An oxidizing agent is reduced and a reducing agent is oxidized.  Variable oxidation numbers exist for transition metals and for most main-group non-metals.

Application & Skills (what do I need to DO?)  Deduction of the oxidation states of an atom in an ion or a compound.  Deduction of the name of a transition metal compound from a given formula, applying oxidation numbers represented by Roman numerals.  Identification of the species oxidized and reduced and the oxidizing and reducing agents, in redox reactions.

There are several definitions for oxidation and reduction:  The first definition has to do with the loss or gain of oxygen:  At the simplest form oxidation can be a reaction that occurs when a substance combines with oxygen 2Ca (s) + O 2(g)  2 CaO (s) CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g)  Reduction can occur with the removal of oxygen NiO (s) + C (s)  Ni (s) + CO (g)  Oxidation is gain of oxygen  Reduction is loss of oxygen Definitions of Oxidation and Reduction Oxidation of metals results in corrosion and rust Fruit gets oxidized when exposed to oxygen, turning it brown.

There are several definitions for oxidation and reduction:  The second definition has to do with the loss or gain of hydrogen:  Oxidation loses hydrogen CH 3 CH 2 OH (l)  CH 3 CHO (l) + H 2(g)  Reduction gain of hydrogen C 2 H 2 + H 2  C 2 H 4 Definitions of Oxidation and Reduction Human Spit Could Cause Indian Bridge to Collapse spit from betel nut is causing corrosion of the Howrah bridge in Calcutta

Many important chemical reactions involve a transfer of electrons Mg (s) + O 2(g)  MgO (s) In this reaction, the Mg will _________ electrons to become Mg 2+ In this reaction, the O will _______ electrons to become O 2- Definitions of Oxidation and Reduction

Oxidation: a loss of electrons Reduction: a gain of electrons OIL RIG 2Mg (s) + O 2(g)  2MgO (s) Which substance is being oxidized? Which substance is being reduced? Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation

Definitions of Oxidation and Reduction OIL RIG is a great method IF the bonds are ionic, but, what about when there is no transfer of electrons? C (s) + O 2(g)  CO 2(s) Last Definition for Oxidation and Reduction requires assigning oxidation states to each element in the reaction Oxidation state (number): the charge of an atom in ionic form or in a molecule Oxidation: the oxidation state increases Reduction: Oxidation state decreases

To Summarize OXIDATION  Gain Oxygen  Lose Hydrogen  Lose Electrons  Oxidation state increases REDUCTION  Lose Oxygen  Gain Hydrogen  Gain electrons  Oxidation state decreases 9

All elements in a compound (even covalent compounds) can be assigned oxidation states. It is a convenient form of “bookkeeping” and will assist in balancing complex equations. Deduce the oxidation state of an element in a compound

Rules for assigning oxidation states (o.s.) 1.For any atom in its elemental form, the o.s. is zero. Mg, S, H 2, P 4 all 0 2.For any monatomic ion, the o.s. equals the charge on the ion. Mg 2+ is +2; Cl - is -1 (Group 1 +1, Group 2 +2, Al +3) 3.The o.s. of oxygen is usually -2, except peroxides like Na 2 O 2 and H 2 O 2, where it is -1 4.The o.s. of hydrogen is +1 when bonded to a nonmetal and -1 when bonded to a metal. 5.The o.s. of Fluorine is -1. The o.n. of the other halogens is -1 except when combined with oxygen. 6.The sum of the o.s. of all atoms in a neutral compound is zero. 7.The sum of the o.s. in a polyatomic ion equals the charge on the ion.

Deduce the oxidation state of an element in a compound H 2 S S 8 SCl 2 Na 2 SO 3 SO 4 2- H 2 O 2 H is +1 (rule 4) ; S is -2 (rule 2) S is 0 (rule 1) Cl is -1 (rule 5); S is +2 (rule 6) Na is +1 (rule 2); O is -2 (rule 3); S is +4 (rule 6) O is -2 (rule 3); S is +6 (rule 7) H is +1 (rule 4); O is -1 (rule 3-peroxide) Determine the oxidation state of each element in the following compounds.

Deduce the oxidation state of an element in a compound Determine the oxidation number (state) of each element in the following compounds. P 2 O 5 P is _____; O is _____ NaHNa is _____; H is _____ Cr 2 O 7 -2 Cr is_____; O is _____ SnBr 4 Sn is_____; Br is_____ HClO 4 H is _____; Cl is _____; O is _____ NO 2 - N is _____; O is _____ N 2 N is _____ Ca(NO 3 ) 2 Ca is _____; N is _____; O is _____ BaO 2 Ba is _____; O is _____

Deduce the oxidation state of an element in a compound Determine the oxidation number (state) of each element in the following compounds. P 2 O 5 P is +5; O is -2 NaHNa is +1; H is -1 Cr 2 O 7 -2 Cr is +6; O is -2 SnBr 4 Sn is +4; Br is -1 HClO 4 H is +1; Cl is +7; O is -2 NO 2 - N is +3; O is -2 N 2 N is 0 Ca(NO 3 ) 2 Ca is +2; N is +5; O is -2 BaO 2 Ba is +4; O is -2

State the names of compounds containing transition metals using oxidation states

Many metals can have more than one oxidation state. Exceptions are alkali metals (all +1), alkaline earth metals (all +2), zinc (+2), aluminum (+3) & silver (+1). These are identified using Roman numerals to denote the charge. Iron(II) is Fe 2+ (ferrous) Iron(III) is Fe 3+ (ferric) Copper(I) is Cu +1 Copper(II) is Cu +2 Name the following compounds using oxidation states. (Use bonding) SnCl 4 _________________________________ Cr(NO 3 ) 3 _________________________________ KOH_________________________________ PbSO 4 _________________________________ CuBr_________________________________ Tin (IV) chloride Chromium (III) nitrate Potassium Hydroxide Lead (II) sulfate Copper (I) bromide

Deduce the oxidation states of each atom (marked x ) in the following: Cr x 2 O 7 2- H 3 As x O 3 Pt x Cl 6 2- Sn x F 2 H 4 P x 2 O 7 Mo x O (x) + 7(-2) = -2 x = +6 Cr 6+ 3(+1)+x + 3(-2) = 0 x = +3 As 3+ x + 6(-1) = -2 x = +4 Pt 4+ x + 2(-1) = 0 x = +2 Sn 2+ 4(+1)+2(x) + 7(-2) = 0 x = +5 P 5+ x + 4(-2) = -2 x = +6 Mo 6+

Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) Assign oxidation states to both reactants and products: Mg + 2HCl  MgCl 2 + H 2 Mg:0; H:+1; Cl:-1  Mg:+2; Cl:-1; H:0 Which species increased in o.s.? That is the one being oxidized (losing electrons) Mg is going from 0 to +2 so is oxidized Which species decreased in o.s.? That is the one being reduced (gaining electrons) H is going from +1 to 0 so is reduced

Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s) Assign oxidation states to both reactants and products: Cu + 2AgNO 3  Cu(NO 3 ) 2 + 2Ag Cu:0; Ag:+1; N:+5; O:-2  Cu:+2; N:+5; O:-2; Ag:0 Which species increased in o.n.? That is the one being oxidized (losing electrons) Cu is going from 0 to +2 so is oxidized Which species decreased in o.n.? That is the one being reduced (gaining electrons) Ag is going from +1 to 0 so is reduced

Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: I 2 O 5 (s) + 5CO(g)  I 2 (s) + 5CO 2 (g) Assign oxidation states to both reactants and products: I 2 O 5 (s) + 5CO(g)  I 2 (s) + 5CO 2 (g) I:__; O:__; C:__; O:__  I:__; C:__; O:__ Which species increased in o.n.? That is the one being oxidized (losing electrons) Which species decreased in o.s.? That is the one being reduced (gaining electrons)

Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: 2Hg 2+ (aq) + N 2 H 4 (aq)  2Hg(l)  N 2 (g) + 4H + (aq) Deduce what is being oxidized and what is being reduced in: Cl 2 (g) + H 2 O(l)  HCl(aq) + HClO(aq)

Identify the oxidizing and reducing agents Oxidizing agent: causes another species to get oxidized & therefore is reduced in the reaction. Reducing agent: causes another species to get reduced & gets therefore gets oxidized in the reaction. Identify the oxidizing and reducing agents in the following: Fe + V 2 O 3  Fe 2 O 3 + VO Assign oxidation states Fe: 0; V: +3; O: -2  Fe: +3; O: -2; V: +2 Deduce what is being oxidized and what is being reduced Fe is oxidized and V is reduced So Fe is the reducing agent and V 2 O 3 is the oxidizing agent

Identify the oxidizing and reducing agents Identify the oxidizing and reducing agents in the following reaction: Mg + HCl  MgCl 2 + H 2 K 2 Cr 2 O 7 + SnCl 2 + HCl  CrCl 3 + SnCl 4 + KCl + H 2 O Mn(NO 3 ) 2 + NaBiO 3 + HNO 3  HMnO 4 + Bi(NO 3 ) 3 + NaNO 3 + H 2 O Assign oxidation states Deduce what is being oxidized and what is being reduced Deduce oxidizing and reducing agents

HOMEWORK Read pp. 209 – 216 Quick Questions p. 215 &