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IB topic 9 Oxidation-reduction Define oxidation and reduction in terms of electron loss and gain.

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Presentation on theme: "IB topic 9 Oxidation-reduction Define oxidation and reduction in terms of electron loss and gain."— Presentation transcript:

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2 IB topic 9 Oxidation-reduction Define oxidation and reduction in terms of electron loss and gain.

3  Taking notes  Do not copy, write in your own words or draw diagrams or pictures  10 % better performance if you copy  35% better performance if you write in your own words

4  2Mg + O 2  2MgO  Reduction-charge goes down  OILRIG  Redox always occurs together  Question 1

5  A:

6 BB

7 CC

8 DD

9 9.2Redox equations  Deduce simple oxidation and reduction half-equations given the species involved in a redox reaction.  2Fe + 3Cl 2  2FeCl 3

10 Deduce the oxidation number of an element in a compound.  + means loss, – gain of e -  Rules  Elements Na, O 2, S 8 = 0  Group 1 = +1 H=+1  O = -2 halides -1  Many exceptions  Ox. # add up to the charge on the species  In covalent compounds more electronegative is – ie NH 3, CCl 4

11  Give Ox. numbers to each element  H 2 SO 4, SO 3 2-  NH 4 +, Fe 2 O 3, K 2 Cr 2 O 7, CuCl 2,  Question 2  Question 3

12 State the names of compounds using oxidation numbers.  MnO 2, FeO, CuCl, Na 2 O  Manganese (IV) oxide, iron (II) oxide, Copper (I) chloride, sodium oxide  [Cu(H 2 O) 6 ] 2+ [CuCl 4 ] 2-  Hexaaquacopper(II) ion  Tetrachlorocopper (II) ion

13 Deduce whether an element undergoes oxidation or reduction in reactions using oxidation numbers.  Ca + Sn 2+  Ca 2+ + Sn  4NH 3 + 5O 2  4NO + 6H 2 O  Disproportionation Cl 2 + H 2 OHCl + HClO  Question 4

14 Deduce redox equations using half- equations.  Steps  Assign O numbers and write half reactions  Balance atoms other than H and O  Balance O by adding H 2 O as needed  Balance H by adding H + as needed  Balance Charges by adding e - to the + side  Equalize the e - by multiplying  Add the half reactions together

15  Try NO Cu  NO + Cu 2+  +5, -2, 0 on left +2,-2,+2 on right  Cu  Cu 2+ ox NO 3 -  NO red  4H + + NO 3 -  NO + 2 H 2 O  Cu  Cu e-  4H + + NO e- NO + 2 H 2 O  8H + + 2NO e- + 3Cu  2NO + 4H 2 O + 3Cu e-

16 Fe +2 + MnO 4 -  Fe +3 + Mn +2

17 SO Cr 2 O 7 2-  SO Cr 3+

18  Internet example Internet example  Question 5

19 Define the terms oxidizing agent and reducing agent.  A substance that gets reduced causes oxidation so it is an oxidizing agent

20  Identify the oxidizing and reducing agents in redox equations.  Fe 2 O 3 + 3C  2Fe + 3CO 2  Fe oxidizing C reducing  IO I - + 6H +  3I 2 +3H 2 O  IO 3 - oxidizing I - reducing  question 6

21 9.3Reactivity  Deduce a reactivity series based on the chemical behavior of a group of oxidizing and reducing agents.  More reactive metals lose their e - more readily becoming a strong reducing agent  Zn + CuSO 4  Stronger Mg, AL, Zn, Fe, Pb, Cu, Ag  simulation simulation

22  Non metals F 2 strongest oxidizing agent, most readily becomes reduced Cl 2, Br 2, I 2  Question 7

23 Deduce the feasibility of a redox reaction from a given reactivity series.  Yes or no  ZnCl 2 + Ag  2FeCl Mg  Cl 2 + 2KI  question 8

24 9:4 Voltaic Cells (battery) Explain how a redox reaction is used to produce electricity in a voltaic cell Zn(s) → Zn 2+ (aq) + 2e - red. Agent Other half cell Cu e - → Cu(s) reduced This combination is a voltaic cell

25 State that oxidation occurs at the negative electrode (anode) and reduction occurs at the positive electrode (cathode) Which is the anode (where e- leave) /cathode? Draw this setup. AAAA nnnn iiii mmmm aaaa tttt iiii oooo nnnnDraw Zn/Zn2+ and Ag/Ag+ and give the potential, show the flow of e- Where is oxidation and reduction

26 Connect these half cells with a salt bridge this is a spontaneous reaction Animation Question 9

27 9:5 Electrolytic cells Describe, using a diagram, the essential components of an electrolytic cell. Opposite of a voltaic cell Requires electrical energy │‌ means + then – in diagrams AAAA nnnn iiii mmmm aaaa tttt iiii oooo nnnn

28 The power source pushes e- to the – electrode -electrode attracts + ions -electrode is the cathode cations gain e- so are reduced Show the electrolysis of MgF 2

29 Describe how current is conducted in an electrolytic cell Do questions 10

30 Deduce the products of the electrolysis of a molten salt Diagram the electrolysis of molten(melted) NaCl Tell where oxidation and reduction occurs Do question 11

31 19.1 Standard electrode potentials Describe the standard hydrogen electrode.

32 Standard H cell Conditions - Pt electrode H 2 gas at 1 atm pressure 1 mol dm -3 H K or 25 o C 0.00 V Attach a half cell if e- flows to H 2 it is – Like Zn which is V

33 conventions Zn(s)/Zn +2 ││H + (aq)/1/2 H 2 (g) (Pt) Oxidation on left side More – value of electrode potentials give off e-

34 Define the term standard electrode potential (E Ö ). relative electrode potential compared under standard conditions with the standard hydrogen electrode relative electrode potential compared under standard conditions with the standard hydrogen electrode Look at your data booklet

35 Calculate cell potentials using standard electrode potentials. Try Cr 2 O 7 2- and Br 2 Answer 0.26 V

36 Predict whether a reaction will be spontaneous using standard electrode potential values. Can a solution of tin II ions reduce a solution of iron III ions? Yes 0.91V

37 Can a solution of Sn 4+ ions reduce Fe 3+ to Fe Sn e- → Sn 2+ E o = No what does work Do question 12

38 19.2 Electrolysis Predict and explain the products of electrolysis of aqueous solutions. For water need DC in a dilute solution of H 2 SO 4 H + to H 2 given off at the – electrode OH - to O 2 at the + electrode 2H 2 O  4H + + O e-

39 Electrolysis of NaCl (aq) - electrode H 2 + electrode dilute OH - to O 2 conc Cl - to Cl 2 Write half reactions Do question 13

40 Determine the relative amounts of the products formed during electrolysis. Position in the electrochemical series + ions lower in the series will gain e- at the – electrode (cathode) in preference to those higher Hydroxide ions release e- to form oxygen and H 2 O in preference to other anions at the positive electrode

41 In some cases concentrations ( more concentrated may be discharged) Nature of the electrode C and Pt are inert List all the cations and anions Cations lower in the series gain e- more readily

42 Describe the use of electrolysis in electroplating. CuSO 4(aq) with copper electrodes Cu 2+ goes to – electrode and plates Cu + electrode Cu goes to Cu 2+ (use impure ore)

43 Electroplating Object to be electroplated is put at the negative electrode and is placed in a solution of ions of the metal used to plate it.

44 Factors affecting relative amounts Charge on the ions Na + Cu 2+ Al 3+ Al takes more energy to make Quantity of e- (amperage and time) charge = current x time Do question 14

45 Do questions 1-14 on chapter 10 in your IB Study Guide and turn in


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