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CHEMISTRY 161 Oxidation-Reduction Reactions Chapter 6.

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Presentation on theme: "CHEMISTRY 161 Oxidation-Reduction Reactions Chapter 6."— Presentation transcript:

1 CHEMISTRY 161 Oxidation-Reduction Reactions Chapter 6

2 REVISION HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) H + (aq) + OH - (aq) → H 2 O(l) (Arrhenius) HCl(aq) + NH 3 (aq) → NH 4 Cl(aq) H + (aq) + NH 3 (aq) → NH 4 + (aq) (Bronsted)

3 CHEMICAL REACTIONS a) precipitation reactions b) acid-base reactions (proton transfer) c) oxidation-reduction reactions (electron transfer) (redox reactions)

4 1. oxidation KEY CONCEPTS loss of electrons 2. reduction acceptance of electrons NUMBER OF ELECTRONS MUST BE CONSERVED

5 1. oxidation EXAMPLE 2. reduction !!!balance electrons!!! Na + Cl - Na  Na + + e Cl e  2 Cl - CaO, Al 2 O 3

6 substance that lost the electrons reduction agent substance that gained the electrons oxidizing agent oxidizing agent is reduced reducing agent is oxidized 2 Na + Cl 2  2 Na + Cl -

7 EXAMPLE 1 solid state reaction of potassium with sulfur to form potassium sulfide EXAMPLE 2 solid state reaction of iron with oxygen to form iron(III)oxide

8 OXIDATION NUMBER ionic compounds ↔ molecular compounds NaClHF, H 2 Na + Cl - ? electrons are fully transferred covalent bond charges an atom would have if electrons are transferred completely

9 HF H + + F - molecular compoundionic compound F - oxidation state -1 H + oxidation state +1 EXAMPLE 1

10 H2OH2O molecular compound ionic compound 2 H + + O 2- H + oxidation state +1 O 2- oxidation state -2 EXAMPLE 2

11 H2H2 molecular compound ionic compound H + + H - EXAMPLE 3 OXIDATION NUMBER OF FREE ELEMENTS IS ZERO

12 RULE 1 OXIDATION NUMBER OF FREE ELEMENTS IS ZERO H 2, O 2, F 2, Cl 2, K, Ca, P 4, S 8

13 RULE 2 monoatomic ions oxidation number equals the charge of the ion group I M + group II M 2+ group III M 3+ (Tl: also +1) group VII (w/ metal) X -

14 RULE 3 oxidation number of hydrogen +1 in most compounds (H 2 O, HF, HCl, NH 3 ) -1 binary compounds with metals (hydrides) (LiH, NaH, CaH 2, AlH 3 )

15 RULE 4 oxidation number of oxygen -2 in most compounds (H 2 O, MgO, Al 2 O 3 ) -1 in peroxide ion (O 2 2- ) (H 2 O 2, K 2 O 2, CaO 2 ) -1/2 in superoxide ion (O 2 - ) (LiO 2 )

16 RULE 5 oxidation numbers of halogens F: -1 (KF) Cl, Br, I: -1 (halides) (NaCl, KBr) Cl, Br, I: positive oxidation numbers if combined with oxygen (ClO 4 - )

17 RULE 6 charges of polyatomic molecules must be integers (NO 3 -, SO 4 2- ) oxidation numbers do not have to be integers -1/2 in superoxide ion (O 2 - )

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19 MENUE 1.oxidation states of group I – III metals 2.oxidation state of hydrogen (+1, -1) 3. oxidation states of oxygen (-2, -1, -1/2, +1) 4.oxidation state of halogens 5.remaining atoms

20 oxidizing agents OCl - Cl - ????? EXP1

21 reducing agent 2 Na + 2 H 2 O  H NaOH EXP2

22 NO NO 2 NO + NO - NO 2 - NO 3 - PO 4 3- SO 4 2- SO 3 SO 2 KO 2 K2OK2O BrO - KClO 4

23 1.redox reactions 2. oxidation versus reduction 3. oxidation numbers versus charges 4. calculation of oxidation numbers REVISION

24 TYPES OF REDOX REACTIONS 1.combination reactions A + B → C 2. decomposition reactions C → A + B 3. displacement reactions A + BC → AC + B 4. disproportionation reactions

25 1.combination reactions A + B → C two or more compounds combine to form a single product S 8 (s) + O 2 (g) → SO 2 (g) 1.oxidation numbers 2. balancing charges

26 MENUE 1.oxidation states of group I – III metals 2.oxidation state of hydrogen (+1, -1) 3. oxidation states of oxygen (-2, -1, -1/2, +1) 4.oxidation state of halogens 5.remaining atoms

27 2. decomposition reactions C → A + B breakdown of one compound into two or more compounds HgO(s) → Hg(l) + O 2 (g) 1.oxidation numbers 2. balancing charges KClO 3 (s) → KCl(s) + O 2 (g)

28 3. displacement reactions A + BC → AC + B an ion or atom in a compound is replaced by an ion or atom of another element 3.1. Hydrogen displacement 3.2. Metal displacement 3.3. Halogen displacement

29 3.1. Hydrogen displacement group I and some group II metals (Ca, Sr, Ba) react with water to form hydrogen Na(s) + H 2 O(l) → NaOH + H 2 (g) less reactive metals form hydrogen and the oxide in water (group III, transition metals) Al(s) + H 2 O(l) → Al 2 O 3 (s) + H 2 (g)

30 3.1. Hydrogen displacement even less reactive metals form hydrogen in acids Zn(s) + HCl(aq) → ZnCl 2 (aq) + H 2 (g) EXP3

31 Li K Ba Ca Na Mg Al Zn Cr Fe Cd Co Ni Sn Pb H Cu Hg Ag Pt Au activity series of metals displace H from water displace H from steam displace H from acids

32 Li K Ba Ca Na Mg Al Zn Cr Fe Cd Co Ni Sn Pb H Cu Hg Ag Pt Au likes to donate electrons does not like so much to donate electrons EXP4

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34 3.2. Metal displacement V 2 O 5 (s) + 5 Ca(s) → 2 V(s) + 5 CaO(s) TiCl 4 (g) + 2 Mg (l) → Ti(s) + 2 MgCl 2 (l)

35 3.3. Halogen displacement F 2 > Cl 2 > Br 2 > I 2 reactivity (‘likes’ electrons) Cl 2 (g) + 2 KBr(aq) → 2 KCl(aq) + Br 2 (l) 00+1 Br 2 (g) + 2 KI(aq) → 2 KBr(aq) + I 2 (s)

36 4. disproportionation reactions an element in one oxidation state is oxidized and reduced at the same time H 2 O 2 (aq) → 2 H 2 O(l) + O 2 (g) Cl 2 (g) + 2 OH - (aq) → ClO - (aq) + Cl - (aq) + H 2 O(l)

37 SUMMARY 1.combination reactions A + B → C 2. decomposition reactions C → A + B 3. displacement reactions A + BC → AC + B 4. disproportionation reactions

38 Homework Chapter 4, p problems


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