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{ Unit 7: Redox & Electrochemistry. What information does the oxidation number give you?

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Presentation on theme: "{ Unit 7: Redox & Electrochemistry. What information does the oxidation number give you?"— Presentation transcript:

1 { Unit 7: Redox & Electrochemistry

2 What information does the oxidation number give you?

3 Electrical production (batteries, fuel cells) Why electrochemistry? REDOX reactions are important in … Purifying metals (e.g. Al, Na, Li) Producing gases (e.g. Cl 2, O 2, H 2 ) Electroplating metals Protecting metals from corrosion Balancing complex chemical equations Sensors and machines (e.g. pH meter) C 3 H 8 O + CrO 3 + H 2 SO 4  Cr 2 (SO 4 ) 3 + C 3 H 6 O + H 2 O

4  REDOX stands for REDuction/OXidation  Oxidation is often thought of as a combination of a substance with oxygen (rusting, burning)  Oxidation refers to a loss of e -  Reduction refers to a gain of e - What is Redox? Loss Electrons = Oxidation Gain Electrons = Reduction Remember: LEO the lions says GERRRRRR!

5 Reactions What is happening to the Fe atom? Fe is going from 0 to +3 oxidation # It must be losing electrons Loss of Electrons = Oxidation In conclusion, the iron atom is being oxidized

6 Reactions What is happening to the Sulfur atom? S is going from 0 to -2 oxidation # It must be gaining electrons Gain of Electrons = Reduction In conclusion, the sulfur atom is being reduced

7 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom - there are a few rules to help us out Na  Na 0 H2H2  H20H20 F2F2  F20F20

8 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom H is ALWAYS +1 (for us) Disclaimer – there are compounds where H has a -1 oxidation number, but we don’t deal with them at this level of chemistry.

9 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom O is ALWAYS -2 (for us)

10 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom Sodium ion  Na +1 Calcium ion  Ca +2 Sulfur ion  N -3 Nitrogen ion  S -2

11 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom NaCl  Na +1 Cl -1 AsI 5  As +5 I 5 -1 Cu(NO 3 ) 2  H 2 +1 Cr 2 +6 O 7 -2 H 2 Cr 2 O 7  Cu +2 (N +5 O 3 -2 ) 2

12 Oxidation Numbers - the charge an atom would have if the electrons belonged to the more EN atom (SO 4 ) -2  (S +6 O 4 -2 ) -2 (NO 3 ) -  (N +5 O 3 -2 ) - (Cr 2 O 4 ) -2  (Cr 2 +3 O 4 ) -2

13 Oxidation Numbers Do the five problems on your notes sheet a. Cr 2 O 3 b. H 2 Cr 2 O 7 c. AsCl 5 d. KCl e. Mg(OH) 2

14 What things are conserved during a chemical reaction?

15 What is reduced/oxidized? Identify in the following reactions what is oxidized and what is reduced 2K + Cl 2  2KCl K 0 – goes from 0 to +1, it is oxidized Cl 0 – goes from 0 to -1, it is reduced

16 Practice Identify in the following reactions what is oxidized and what is reduced 2NaCl + 3SO 3  Cl 2 + SO 2 + Na 2 S 2 O 7 Cl -1 – goes from -1 to 0, it is oxidized S +6 – goes from +6 to +4, it is reduced

17 Practice Identify in the following reactions what is oxidized and what is reduced Zn + Pb +2 (aq)  Zn +2 (aq) + Pb Zn 0 – goes from 0 to +2, it is oxidized Pb +2 – goes from +2 to 0, it is reduced

18 a. C + H 2 SO 4  CO 2 + SO 2 + H 2 O b. HNO 3 + HI  NO + I 2 + H2O c. KMnO 4 + HCl  MnCl 2 + Cl 2 + H 2 O + KCl d. Sb + HNO 3  Sb 2 O 5 + NO + H 2 O e. HCl + MnO 2  MnCl 2 + H 2 O + Cl 2

19 a. C + H 2 SO 4  CO 2 + SO 2 + H 2 O b. HNO 3 + HI  NO + I 2 + H 2 O c. KMnO 4 + HCl  MnCl 2 + Cl 2 + H 2 O + KCl d. Sb + HNO 3  Sb 2 O 5 + NO + H 2 O e. HCl + MnO 2  MnCl 2 + H 2 O + Cl 2

20 1. C + 2Cl 2  CCl 4 Ox – Red – 2. H 2 + Cl 2  2HCl Ox – Red – 3. 2P + 3Cl 2  2PCl 3 Ox – Red – 4. C + H 2 O  CO + H 2 Ox – Red – 5. Fe + 3Cl 2  2FeCl 2 Ox – Red –

21 6. 2Al + 3Br 2  2AlBr 3 Ox – Red – 7. Pb + 2HCl  PbCl 2 + H 2 Ox – Red – 8. SiO 2 + 2C  Si + 2CO Ox – Red – 9. CO 2 + 2Mg  2MgO + C Ox – Red – 10. H 2 SO 4 + Zn  ZnSO 4 + H 2 Ox – Red -

22 Identify what atom is oxidized and what atom is reduced: Fe + 2HCl  FeCl 2 + H 2

23 HALF REACTIONS Fe e-  Fe Reduction: Shows only one half of the reaction, including the e- lost or gained -notice that there is a conservation of charge and mass Oxidation: OR Fe  Fe e- OR Fe - 3e-  Fe 3+

24 HALF REACTIONS Cu + AgNO 3  Cu(NO 3 ) 2 + Ag Reduction: Write both half reactions for the following reaction: Oxidation: Ag +  Ag Cu  Cu e - Cu  Cu +2 Ag + + 1e -  Ag Cu - 2e -  Cu +2

25 HALF REACTIONS HNO 3 + I 2  HIO 3 + NO 2 Reduction: Write both half reactions for the following reaction: Oxidation: N +5  N +4 I 2 0  2I e - I 2 0  I +5 N e -  N +4 I e -  2I +5

26 Sn + AgNO 3  Sn(NO 3 ) 2 + Ag Reduction: Write both half reactions for the following reaction: Oxidation: Ag +1  Ag 0 Sn 0  Sn e - Sn 0  Sn +2 Ag e -  Ag 0 Sn 0 - 2e -  Sn +2 Half Reactions

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28 Redox Lab Al + CuCl 2  Mass GFM Moles Cu + AlCl

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30 If you were to react Cu and Nickel(II) Chloride what would the products be? How much metal could you make if you started with 2.00g of Cu?

31 Oxidizing and Reducing Agents Oxidizing Agent  Reducing Agent  - causes the oxidation of another atom - oxidation number decreases - causes the reduction of another atom - oxidation number increases Ca + Cl 2  CaCl 2 What is the O.A.? What is the R.A.?  Cl  Ca - it is actually the atom that is REDUCED - it is actually the atom that is OXIDIZED

32 PRACTICE 4HCl + MnO 2  MnCl 2 + 2H 2 O + Cl 2 Oxidizing Agent: Reducing Agent:  Mn +4  Cl - In the equation below, identify what is oxidized what is reduced. Also identify the oxidizing and reducing agent. Reduced: Oxidized:  Cl -  Mn +4

33 Deals with chemical reactions that either produce electricity or need electricity to occur! ELECTROCHEMICAL CELLS There are 2 types of ELECTROCHEMICAL CELLS. same Some things that are the same for both types of cells: 1. The RED CAT GETS FAT! 2. Electrons always flow from the anode to the cathode! Anorexic Ox Electrochemical Reactions Electrochemical Reactions

34 Cu Cu electrode Zn Zn electrode Lose e- (Table J) Oxidized Anode (-) Gains e- (Table J) Reduced Cathode(+) 2e- Zn +2 Cu +2 ZnSO 4 CuSO 4 Will this go on forever? Half Reactions

35 Cu Cu electrode Zn Zn electrode Lose e- (Table J) Oxidized Anode (-) Gains e- (Table J) Reduced Cathode(+) Zn +2 ZnSO 4 CuSO 4 Will this go on forever? Half Reactions

36 ZnSO 4 CuSO 4 Cu Cu electrode Zn Zn electrode Lose e- (Table J) Oxidized Anode (-) Gains e- (Table J) Reduced Cathode(+) Na + Cl - Na + Cl - Na + Cl - Na + Cl - 2e- Zn +2 2e- Cu +2 2Cl - 2Na + Electrochemistry

37 Half Reactions

38 In the reaction below, identify what is the oxidizing agent and the reducing agent. Ca + H 2 O  CaO + H 2

39 ZnSO 4 CuSO 4 Cu Cu electrode Zn Zn electrode Lose e- (Table J) Oxidized Anode (-) Gains e- (Table J) Reduced Cathode(+) Na + Cl - Na + Cl - Na + Cl - Na + Cl - 2e- Zn +2 2e- Cu +2 2Cl - 2Na + Electrochemistry

40 Summary: 1.Voltaic Cells – are spontaneous reactions Electrons travel through the wire from more reactive metal to the less reactive metal (Table J) 2. Electrons travel through the wire from more reactive metal to the less reactive metal (Table J) 3.Salt Bridge – permits the flow of ions 4.Red Cat gets fat! Electrochemistry

41 These are NOTspontaneous reactions – they areforcedby the addition of electricity! These are NOT spontaneous reactions – they are forced by the addition of electricity! Occur within one container, not two separate cells! These reactions are used to plate metals, purify metals and separate compounds. Electrochemistry

42 Sn Fe Electrochemistry Cathode Becomes negative Picks up + ions from solution Gets plated with the metal ion from the solution Anode Becomes positive Loses positive ion (Sn +2 ) to solution

43 During a laboratory activity, a student reacted a piece of zinc with 0.1M HCl (aq). Based on Reference Table J, identify one metal that does not react spontaneously with HCl (aq).

44 K K electrode Fe Fe electrode NaBr K +1 Fe +2 Write out the oxidation and reduction half reactions for the voltaic cell below. (Do not need drawing in notes)

45 Electrochemical Cell Differences spontaneous non-spontaneous Anode - negative Anode - positive Electrochemistry Needs two containers Needs one container

46 Packet Review 16. K K electrode Fe Fe electrode NaBr K +1 Fe +2

47 Packet Review 16. Ag Ag electrode Al Al electrode Na 2 SO 4 Al +3 Ag +1

48 Cu Zn Anode Cathode Electrons ALWAYSflow from Anode to Cathode Electrons ALWAYS flow from Anode to Cathode Becomes negative Picks up + ions from solution Cu +2 Gets plated with the metal ion from the solution Becomes positive Loses positive ion (Cu +2 ) to solution Electrochemistry

49 Electrochemistry And review packet

50 Cu Zn Anode Cathode Electrons ALWAYSflow from Anode to Cathode Electrons ALWAYS flow from Anode to Cathode Becomes negative Picks up + ions from solution Cu +2 Gets plated with the metal ion from the solution Becomes positive Loses positive ion (Cu +2 ) to solution Electrochemistry

51 Electrochemistry Balancing Net Ionic Equations Done on the board

52 Electrochemistry Electrolysis Simulation Ionic equation balancing

53 { Balancing equations using oxidation numbers C 3 H 8 O + CrO 3 + H 2 SO 4  Cr 2 (SO 4 ) 3 + C 3 H 6 O + H 2 O

54 BALANCING REACTIONS -conservation of mass and charge -we must make sure that the e- that one atom loses must equal the e- that another atom gains HNO 3 + I 2  HIO 3 + NO 2 + H 2 O Try to balance this one:

55 BALANCING REACTIONS HNO 3 + I 2  HIO 3 + NO 2 + H 2 O 1. Assign ox #’s, write ½ reactions and cross out spectators N e -  N +4 I e -  I Balance each ½ reaction with respect to atoms and then e - N e -  N +4 I e -  2I )( 3. Distribute to all parts of the ½ reaction 1 )( 10N e -  10N +4 I e -  2I +5

56 BALANCING REACTIONS 3. Carry everything down and cross out e- 10N e -  10N +4 I e -  2I +5 10N +5 + I 2 0  10N I Put coefficients back into equation and balance what is left. 10HNO 3 + 1I 2  10HIO 3 + 2NO 2 + H 2 O4

57 BALANCING REACTIONS Sb + HNO 3  Sb 2 O 5 + NO + H 2 O 1. Assign ox #’s, write ½ reactions and cross out spectators Sb 0  Sb e- N e -  N Balance each ½ reaction with respect to atoms and then e - 3 ) ( 3. Distribute to all parts of the ½ reaction 10 )( 6Sb 0  3Sb e - 10N e -  10N +2 2Sb 0  Sb e - N e -  N +2

58 Most missed Part 2 Questions 1. You have a voltaic cell with copper and aluminum as the electrodes. As the cell operates, the mass of the Al electrode decreases. Explain, in terms of particles, why this decrease in mass occurs. 2. Explain, in terms of electrical energy, how the operation of a voltaic cell differs from the operation of an electrolytic cell used in the Hall process. Include both the voltaic cell and the electrolytic cell in your answer. 3. Explain, in terms of ions, why molten cryolite conducts electricity. [Cryolite = Na 3 AlF 6 ]

59 6Sb + 10HNO 3  3Sb 2 O NO + H 2 O 6Sb 0  3Sb e - 10N e -  10N +2 BALANCING REACTIONS 3. Carry everything down and cross out e- 6Sb 0 +10N +5  3Sb N Put coefficients back into equation and balance what is left. 5

60 Balance the following S + HNO 3  SO 2 + NO + H 2 O

61 The Statue of Liberty is made of an iron framework covered by copper metal. Over time, a thin green layer(patina) forms on the outside. Where the iron came into contact with the copper a reaction occurred where the iron was oxidized. Why did this happen? Use your Reference Tables.


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