Redox Class #1: oxidation + reduction reactions made fun 1.2.3: Redox explains the chemistry behind batteries and electroplating precious metals onto strong base metals. It also explains how to break apart water into hydrogen and oxygen, and lots more. 4: These 2 reactions are always paired and balanced. 5. In the old days, Oxidation meant____________________________________ Reduction meant ___________________________________ Now, the real definitions are Oxidation is: Reduction is: 7. To remember this well say LEO the lion goes GER!
Example 8 Magnesium and sulfur form magnesium sulfide (synthesis) Mg + S MgS Magnesium atom + sulfur atom make ionic magnesium sulfide All atoms are neutral so we can ADD to our drawing like this: Mg + S 9. MgS Those little circles
means neutral Mg + S MgS The magnesium and sulfur atoms are of course neutral, they have equal numbers of protons and electrons (all atoms do). The magnesium sulfide is neutral too, but its formed by the combination of Mg+2 and S-2 ions. Its net neutral, but each ion has an individual charge. Even though we wouldnt write out the charges, what really happens is this:
Mg + S Mg+2S-2 11. In this reaction 2 different things happened... The magnesium lost 2 electrons, the magnesium was oxidized. The sulfur gained 2 electrons, the sulfur was reduced. 12. Redox is the pair of reactions that allows for the balanced transfer of electrons. Redox in this case is synthesis. It can be single replacement, it can be decomp, it can be combustion, etc. Just watch those pesky electrons. 14. The magnesium is oxidized by the sulfur, the sulfur is reduced by the
magnesium 15. Neutral atoms form a neutral ionic compound, but the OXIDATION NUMBERS change, when ions form. If the oxidation numbers change, it s redox. 16. Word EQ: silver nitrate solution + copper yields 17. Balanced chemical equation for that 17. AgNO3(AQ) + Cu(S) CuNO3(AQ) + Ag(S) Let us re-write this with the oxidation numbers that are there only in our minds so we can see
the redox reactions. 18. Ag NO3 Ag(S) (AQ) + Cu (S) Cu NO3 (AQ) +
18. Ag+1NO3-1(AQ) + Cu(S) Ag(S) Cu+1NO3-1 (AQ) + The ionic silver nitrate combines to the neutral atoms of copper. Copper changes into a +1 cation, jumping into solution to combine with the nitrate ions. The silver ions in solution get bumped out as a solid, and these new silver atoms are of course neutral. 19. The Silver Ions ___________ electrons, the Ag +1 are ________________ 20. The Copper atoms ___________ electrons, the Cu are ____________ Ag+1NO3-1(AQ) + Cu(S)
Cu+1NO3-1 (AQ) + Ag(S) The copper atoms lose electrons (LEO) so you can say, the copper atoms are oxidized into copper +1 cations. The silver +1 cations gain electrons to form into silver atoms, so you can say that the silver +1 cations are reduced into silver atoms. 21. The nitrates are just swimming around, available to bond to any cations, they do not participate in the reaction, they just are there. We call these kinds of non-participatory ions the Spectator ions. dont change)
(They Redox in proper form 22. Li + NaCl LiCl + Na ox: red: 23. Lithium is oxidized into the lithium cation The sodium cation is reduced into the sodium atom. Redox in proper form 22. Li + NaCl ox: Li
Li LiCl + Na +1 red: Na + 1e +1 + 1e -1 -1 Na 23. Lithium is oxidized into the lithium cation
The sodium cation is reduced into the sodium atom. 24. The spectator ion is the CHLORIDE Cl-1 24. show the half reactions for this single replacement/redox reaction. Mg + 2HCl MgCl2 + H2 ox: red: 25. Here, the Mg atoms are oxidized into _____________. The H+1 cations are reduced to ________________ 26. In this case, ____ electrons are oxidized, so ____ electrons must be reduced. The electron transfer MUST be in balance!
24. show the half reactions for this single replacement/redox reaction. Mg + 2HCl ox: Mg MgCl2 + H2 Mg+2 + 2e-1 red: 2H + 2e +1 -1 H2 25. Here, the Mg atoms are oxidized into Mg+2 cations
The H+1 cations are reduced to H2 neutral atoms 26. In this case, 2 electrons are oxidized, so 2 electrons must be reduced. The electron transfer MUST be in balance! Write the balanced chemical reaction and the half reactions for this last redox. 27. Sodium atoms + chlorine molecules synthesize into table salt Balanced reaction: ox: red: Tonight: Read the BASICS (no kidding). Go buy a review book too!
Redox Class #2 OB: assigning oxidation numbers plus how batteries (voltaic cells) work. If you read the BASICS this should be easy, if you didnt read the BASICS yet, ask yourself why? Take better care of yourself, youre worth it. 28. Ions have easy oxidation numbers, its just the charge of the ion. For examples: 29. The oxidation number for the sodium cation is _____ For the chloride anion it is ____ For the sulfate anion (table E), its ______ For magnesium cation it is _____ For all atoms (including the HONClBrIF twins) it is ____, because they have no charge. Inside molecules, like carbon dioxide (no ions) there are still oxidation numbers.
Take your reference tables out now, periodic table, please. 31. What are the individual oxidation numbers for all of these species? (they better sum to zero!) CO2 PCl3 PCl5 CO CaCl2 H2SO4
Cr2O7-2 NbBr5 31. What are the individual oxidation numbers for all of these species? (they better sum to zero!) CO2 C+4 O-2 PCl3 P+3 Cl-1Cl-1Cl-1 PCl5 P+5 Cl-1Cl-1Cl-1Cl-1Cl-1 CO C+2 O-2 H2SO4 H+1H+1S+6 and 4O-2 CaCl2 Ca+2 Cl-1Cl-1 NO2 N+4 O-2 O-2
Cr2O7-2 2Cr+6 and 7O-2 NbBr5 Nb+5 and 5Br-1 single replacement (redox too) reaction Silver nitrate solution plus copper forms copper (II) sulfate solution and silver 32. Write a balanced chemical equation now. 33. What species is oxidized? __________________ 34. What species is reduced? __________________ 35. Name the spectator ion_______________ AgNO3(AQ) + Cu(S) Cu(NO3)2(AQ) + Ag(S) 36. Write the half reactions and the net ionic equation now (WHAT???) ox: ______________________
red: ______________________ NET: _______________________ single replacement (redox too) reaction Silver Nitrate solution plus copper forms Copper (II) sulfate solution and Silver Write a balanced chemical equation now. 2AgNO3(AQ) + Cu(S) Cu(NO3)2(AQ) + 2Ag(S) What species is oxidized? Cu What species is reduced? Ag+1 name the spectator ion NO3-1 Write the half reactions and the net ionic equation now.
ox: Cu Cu+2 + 2e- red: 2Ag+1 + 2eNET: Cu + 2Ag+1 2Ag Cu+2 + 2Ag+1 37. A battery is a voltaic cell. 38. Batteries spontaneously produces electricity. Electricity is the flow of electrons, which can do work like light up your bulb, or start your car, or what ever. Batteries are cute, and neatly packaged, but to learn how they work we sort of have to take them apart to see the details. 39
bulb Were going to label this now. It shows two beakers of solution, with a piece of metal in each one, connected by a wire. Theres also a glass tube with a solution in it connecting the 2 solutions, with cotton balls clogging the ends. At top is a bulb, which would light up if electricity goes through the wire. Go AHEAD bulb KCl(AQ) Salt bridge Zn
ZnSO4(AQ) Cu CuBr2(AQ) 39. Label these PARTS, listen, think Take out table J now bulb KCl(AQ) Salt bridge Zn
ZnSO4(AQ) Cu CuBr2(AQ) 40. How do we decide which of the metals here will oxidize using table J? Label the blank diagram on the second slide. bulb KCl(AQ) Salt bridge Zn
OX Cu ZnSO4(AQ) RED CuBr2(AQ) 41. Oxidation releases electrons, creating cations that jump into solution. Cations are positively charged. These cations jump into a neutral solution, making the solution become ________ charged. 42. This solution, now positively charged, will attract ions from the salt bridge, which will neutralize the solution. A positive solution attracts __________ ions. 43. In the opposite beaker, where cations are forming into atoms on the cathode, the neutral solution is losing the positive cations, making that solution become negatively charged. This negative solution will attract the __________ salt ions to neutralize the solution. bulb
KCl(AQ) Salt bridge Zn OX Cu ZnSO4(AQ) RED CuBr2(AQ) 42 ox: Zn
Zn+2 + 2e- red: Cu+2 + 2e- Cu NET ionic equation: Zn + Cu+2 Zn+2 + Cu Electron flow Electron flow bulb
Cl-1 KCl(AQ) K+1 Salt bridge Zn + Zn+2 OX ZnSO4(AQ)
- Cu Cu+ 2 RED CuBr2(AQ) 45. The ions of the salt bridge balance out the electrical potential that builds up, letting the electricity flow and flow! bulb NaCl(AQ) Salt bridge
Pb PbCl2(AQ) Mg Mg(NO3)2(AQ) 46. Completely label this, OX side, RED side, anode, cathode, direction of electrons, directions of salt ions, and half reactions. 47. Name the 3 reasons that this battery will die. bulb NaCl(AQ) Salt bridge
Pb PbCl2(AQ) Mg Mg(NO3)2(AQ) OX: _____________________________________________________ RED: _____________________________________________________ NET: _____________________________________________________ 47. The 3 Reasons that ALL Batteries Die? A. B. C.
47. The 3 Reasons that ALL Batteries Die? A. Run out of ANODE metal no more oxidation, no more electricity produced B. Run out of CATHODE SIDE CATIONS no more reduction, so no more oxidation either. C. Run out of salt ions solutions get charged, electrons cease their flow. OB: redox class #3 Lots more practice with voltaic cells 48. Label this voltaic cell diagram completely. Write both half reactions, then the net ionic equation. Oxidation: ____________________________________________ Reduction: ________________________________________________ Net Ionic Equation: __________________________________________
State the 3 specific reasons that THIS voltaic cell will die. bulb NaI(AQ) Rb RbF(AQ) Cs CsCl(AQ) ox: _________________________________ red: __________________________________ NET IONIC EQ: ________________________________________
Also name the two solutions and the salt properly. anode bulb e -1 I-1 NaI(AQ) cathode Na+1
e-1 Rb Rb+1 RbF(AQ) OX Cs +1 CsCl(AQ) Cs
RED ox: Rb Rb+1 + 1e-1 red: Cs+1 + 1e-1 Cs NET IONIC EQ: Rb + Cs+1 Rb+1 + Cs Rubidium fluoride, cesium chloride solutions, with sodium iodide salt solution. This cell will die when it runs out of Rubidium anode, Cesium cathode side cations, or runs out of sodium iodide salt solution. bulb
(NH4)2CO3(AQ) Ba Ba(NO3)2(AQ) Sr Sr(C2H3O2)2(AQ) 52. ox: _________________________________ red: __________________________________ NET IONIC EQ: ________________________________________ Also, name the two solutions and the salt properly. 53. Why will this cell die? bulb
anode CO3-2 (NH4)2CO3(AQ) cathode NH4+1 e-1 e-1 Ba Sr Ba+2
Sr+2 Ba(NO3)2(AQ) OX ox: Ba Sr(C2H3O2)2(AQ) RED Ba+2 + 2e-1 red: Sr+2 + 2e-1 Sr
NET IONIC EQ: Ba + Sr+2 Ba+2 + Sr Barium nitrate and strontium hydroxide solutions, ammonium carbonate salt solution. bulb Li3(PO4)(AQ) Ag AgHCO3(AQ) Mg MgCrO4(AQ)
ox: _________________________________ red: __________________________________ NET IONIC EQ: ________________________________________ Also name the two solutions, and the salt, properly. 55. Death of this cell? bulb cathode Li+1 Li3(PO4)(AQ) e-1
with lithium phosphate salt solution OB: Redox Class #4 Voltaic vs. Electrolytic cells Voltaic cells has chemistry spontaneously produce electricity. The other kind of electrochemical cell, the electrolytic cell, uses electricity to make redox chemistry happen. 56. There are two kinds of ELECTROCHEMICAL CELLS, the one we know, the voltaic cell, and a new one called the ________________________ cell. 57. Voltaic cells have chemistry spontaneously creating electricity. An electrolytic cell REQUIRES ____________________ to force a chemical reaction. 58. There are 2 kinds of electrochemical cells, the _____________________ cell and the
_____________________________ cell. 59. When you put copper into silver nitrate solution (which we have done more than once this year) the copper replaces silver in solution, the silver precipitate can be used for a belly button ring, or a bullet for a werewolf. You know this reaction, balance it now. This reaction happens spontaneously because it can happen. ___________________________________________________________________ 60. We can stop that from happening if we use a battery, an outside energy source. Cu(S) + 2AgNO3(AQ) Cu(NO3)2(AQ) + 2Ag(S) AgNO3(AQ) Lets draw in a battery and see what we get. copper battery
AgNO3(AQ) Ag Cu ANODE battery e- e- Reduction happens ON THE CATHODE METAL, so the ring is the cathode.
CATHODE AgNO3(AQ) Ag Ag+1 Oxidation happens ON the silver bar. Cu OX: Ag Ag+1 + 1eRED: Ag+1 + 1e- Ag ANODE battery
e- e- NET: Ag + Ag+1 Ag + Ag+1 CATHODE AgNO3(AQ) Ag Ag+1 Oxidation happens ON the silver bar. Cu
e-1 battery e-1 ANODE Ag(S) AgNO3(AQ) Cu(S) Ag+1
CATHODE 69 Lets try to label this up, electrons from the battery, to the spoon, what happens in the solution, what happens on the gold bar, etc. battery Aluminum spoon AuCl (AQ) Au(S) e-1
e-1 battery Electrons from the battery land on the spoon, which causes the reduction of the Au+1 cations, plating the spoon gold. The gold bar oxidizes gold atoms into cations, and the free electrons from this oxidation replace the electrons from the battery. Aluminum spoon AuCl (AQ) Au
70. ox: Au(S) Au +1 Au+1(AQ) + 1e-1 red: Au+1(AQ) + 1e-1 NET: Au+ Au+1 Au(S) Au + Au+1
e-1 e-1 ANODE Electrons are lost at the anode, so the gold bar is the anode. battery RED CAT Aluminum spoon
AuCl (AQ) Au Au+1 Reduction happens at the cathode, so the spoon is the cathode. Redox Class #5 The electrolysis of water is redox, and showing this using a Hofmann Apparatus
73. Define electrolysis & hydrolysis Fill with water here Add a bit of H2SO4(AQ) to allow water to conduct electricity. 2 tubes filled with water, each with a spigot on top. 74. The electrodes must be connected to a Direct Current power supply (like a strong battery). The electricity forces a non spontaneous redox reaction. 2 platinum electrodes, do not corrode, conduct electricity very well. Attach to power supply here.
H2O(L) decomposes into H2(G) + O2(G) 75. The decomposition of water: 2H2O(L) 2H2(G) + O2(G) Rewrite with oxidation numbers showing H2O(L) decomposes into H2(G) + O2(G) 2H2O(L) 2H2(G) + O2(G)
Rewrite this with oxidation numbers showing +1 2H2 O -2 2H2 + O2 2H2+1O -2 2H2 + O2
76. Write out the half reactions for oxidation and reduction now. Oxidation: ________________________________________________________ Reduction: ________________________________________________________ 77. Name the type of electrochemical cell that can spontaneously produce electricity from a chemical reaction. 78. Name the type of cell where electricity forces a redox reaction that would not be spontaneous. 79. What always happens at the anode? 80. What always happens at the cathode? 81. Is Leo ALWAYS a RED-CAT?
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