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9.1 Oxidation and Reduction Part 1

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

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9.1 Oxidation and Reduction Part 1

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

  2. 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.

  3. 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.

  4. 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 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) + O2(g)  2 CaO(s) • CH4(g) + 2O2(g)  CO2(g) + 2H2O(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

  5. 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 There are several definitions for oxidation and reduction: • The second definition has to do with the loss or gain of hydrogen: • Oxidationloses hydrogen • CH3CH2OH(l)  CH3CHO(l) + H2(g) • Reduction gain of hydrogen • C2H2 + H2  C2H4

  6. Definitions of Oxidation and Reduction Many important chemical reactions involve a transfer of electrons • Mg(s) + O2(g) MgO(s) • In this reaction, the Mg will _________ electrons to become Mg 2+ • In this reaction, the O will _______ electrons to become O2-

  7. Definitions of Oxidation and Reduction Oxidation: a loss of electrons Reduction: a gain of electrons OIL RIG 2Mg(s) + O2(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

  8. 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) + O2(g) CO2(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

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

  10. Deduce the oxidation state of an element in a compound • 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.

  11. Rules for assigning oxidation states (o.s.) For any atom in its elemental form, the o.s. is zero. Mg, S, H2, P4 all 0 For any monatomic ion, the o.s. equals the charge on the ion. Mg2+ is +2; Cl- is -1 (Group 1 +1, Group 2 +2, Al +3) The o.s. of oxygen is usually -2, except peroxides like Na2O2 and H2O2, where it is -1 The o.s. of hydrogen is +1 when bonded to a nonmetal and -1 when bonded to a metal. The o.s. of Fluorine is -1. The o.n. of the other halogens is -1 except when combined with oxygen. The sum of the o.s. of all atoms in a neutral compound is zero. The sum of the o.s. in a polyatomic ion equals the charge on the ion.

  12. Deduce the oxidation state of an element in a compound Determine the oxidation state of each element in the following compounds. • H2S • S8 • SCl2 • Na2SO3 • SO42- • H2O2 • 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)

  13. Deduce the oxidation state of an element in a compound Determine the oxidation number (state) of each element in the following compounds. P2O5 P is _____; O is _____ NaH Na is _____; H is _____ Cr2O7-2 Cr is_____; O is _____ SnBr4 Sn is_____; Br is_____ HClO4 H is _____; Cl is _____; O is _____ NO2- N is _____; O is _____ N2 N is _____ Ca(NO3)2 Ca is _____; N is _____; O is _____ BaO2 Ba is _____; O is _____

  14. Deduce the oxidation state of an element in a compound Determine the oxidation number (state) of each element in the following compounds. P2O5 P is +5; O is -2 NaH Na is +1; H is -1 Cr2O7-2 Cr is +6; O is -2 SnBr4 Sn is +4; Br is -1 HClO4 H is +1; Cl is +7; O is -2 NO2- N is +3; O is -2 N2 N is 0 Ca(NO3)2 Ca is +2; N is +5; O is -2 BaO2 Ba is +4; O is -2

  15. State the names of compounds containing transition metals using oxidation states

  16. 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 Fe2+ (ferrous) Iron(III) is Fe3+ (ferric) Copper(I) is Cu+1 Copper(II) is Cu+2 Name the following compounds using oxidation states. (Use bonding) SnCl4 _________________________________ Cr(NO3)3 _________________________________ KOH _________________________________ PbSO4 _________________________________ CuBr _________________________________ Tin (IV) chloride Chromium (III) nitrate Potassium Hydroxide Lead (II) sulfate Copper (I) bromide

  17. Deduce the oxidation states of each atom (marked x) in the following: • Crx2O72- • H3AsxO3 • PtxCl62- • SnxF2 • H4Px2O7 • MoxO42- • 2(x) + 7(-2) = -2 x = +6 Cr6+ • 3(+1)+x + 3(-2) = 0 x = +3 As3+ • x + 6(-1) = -2 x = +4 Pt4+ • x + 2(-1) = 0 x = +2 Sn2+ • 4(+1)+2(x) + 7(-2) = 0 x = +5 P5+ • x + 4(-2) = -2 x = +6 Mo6+

  18. Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g) Assign oxidation states to both reactants and products: Mg + 2HCl  MgCl2 + H2 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

  19. Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Assign oxidation states to both reactants and products: Cu + 2AgNO3 Cu(NO3)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

  20. Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: I2O5(s) + 5CO(g)  I2(s) + 5CO2(g) Assign oxidation states to both reactants and products: I2O5(s) + 5CO(g)  I2(s) + 5CO2(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)

  21. Identify the species oxidized and reduced Deduce what is being oxidized and what is being reduced in: 2Hg2+(aq) + N2H4(aq)  2Hg(l)  N2(g) + 4H+(aq) Deduce what is being oxidized and what is being reduced in: Cl2(g) + H2O(l)  HCl(aq) + HClO(aq)

  22. 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 + V2O3 Fe2O3 + 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 V2O3 is the oxidizing agent

  23. Identify the oxidizing and reducing agents Identify the oxidizing and reducing agents in the following reaction: Mg + HCl MgCl2 + H2 K2Cr2O7 + SnCl2 + HCl CrCl3 + SnCl4 + KCl + H2O Mn(NO3) 2 + NaBiO3 + HNO3 HMnO4 + Bi(NO3) 3 + NaNO3 + H2O Assign oxidation states Deduce what is being oxidized and what is being reduced Deduce oxidizing and reducing agents

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

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