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Redox Class #2 OB: assigning oxidation numbers plus batteries (voltaic cells) If you read the diary this should be easy, if you didn’t yet read the diary,

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Presentation on theme: "Redox Class #2 OB: assigning oxidation numbers plus batteries (voltaic cells) If you read the diary this should be easy, if you didn’t yet read the diary,"— Presentation transcript:

1 Redox Class #2 OB: assigning oxidation numbers plus batteries (voltaic cells) If you read the diary this should be easy, if you didn’t yet read the diary, ask yourself why? Take better care of yourself, you’re worth it.

2 Ions have easy oxidation numbers, it’s just the charge of the ion. For examples: The oxidation number for the sodium cation is +1 For the chloride anion it is -1 For the sulfate anion (table E), it’s -2 For magnesium cation it is +2 For all atoms (including the HONClBrIF twins) it is zero, 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.

3 What are the oxidation numbers for each atom in each molecule or ion listed? CO 2 CO CaCl 2 NO 2 PCl 3 PCl 5 H 2 SO 4 Cr 2 O 7 -2 NbBr 5

4 What are the oxidation numbers for each atom in each molecule or ion listed? CO 2 C +4 O -2 CO C +2 O -2 CaCl 2 Ca +2 Cl -1 Cl -1 NO 2 N +4 O -2 O -2 PCl 3 P +3 Cl -1 Cl -1 Cl -1 PCl 5 P +5 Cl -1 Cl -1 Cl -1 Cl -1 Cl -1 H 2 SO 4 H +1 H +1 S +6 and 4O -2 Cr 2 O Cr +6 and 7O -2 NbBr 5 Nb +5 and 5Br -1

5 Demo: single replacement (redox too) reaction Silver nitrate solution plus copper forms copper (II) nitrate solution and silver Write a balanced chemical equation now. What species is oxidized? __________________ What species is reduced? __________________ name the spectator ion_______________ Write the half reactions and the net ionic equation now. ½ ox: ______________________ ½ red: ______________________ NET: _______________________

6 Demo: single replacement (redox too) reaction Silver nitrate solution plus copper forms copper (II) nitrate solution and silver Write a balanced chemical equation now. What species is oxidized? Cu° What species is reduced? Ag +1 name the spectator ion NO 3 -1 Write the half reactions and the net ionic equation now. ½ ox: Cu° Cu e - ½ red: 2Ag e - 2Ag ° NET: Cu° + 2Ag +1 Cu Ag ° 2AgNO 3(AQ) + Cu (S) Cu(NO 3 ) 2(AQ) + 2Ag (S)

7 A battery is a voltaic cell, it 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. On this next slide, there is a big (mostly ugly looking at first) diagram. You will have to draw it over and over, and you’ll like it, but probably not right now. So, let me hand you one to start, then you can recopy it over and over.

8 bulb We’re going to label this now. It shows two beakers of solution, with a piece of metal in each one, connected by a wire. There’s also a glass tube with a solution in it, and cotton balls (not drawn) connecting the 2 solutions. At top is a bulb, which would light up if electricity goes through the wire.

9 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) Take out table J now…

10 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) First, decide which metal is going to oxidize and which will be forced to reduce, then we will label this diagram completely. Next slide, write the half reactions and net ionic equation.

11 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) Write the half reactions where they belong, then the net ionic equation too. ½ ox: __________________________ ½ red: ______________________________ NET ionic equation: ______________________________________

12 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) Write the half reactions where they belong, then the net ionic equation too. ½ ox: Zn° Zn e - ½ red: Cu e - Cu° NET ionic equation: Zn° + Cu +2 Zn +2 + Cu°

13 Just to prove I am not afraid, This is my son playing lacrosse. He picked his own number, and I had no trouble with any triskaidekaphobia at all.

14 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) OxidationReduction Zn +2 Cu + 2 Electron flow + - The solutions become charged immediately, stopping the flow of electrons. What will we do?

15 bulb ZnSO 4(AQ) CuSO 4(AQ) Zn Cu Salt bridge K 2 SO 4(AQ) OxidationReduction Zn +2 Cu + 2 Electron flow + - SO 4 -2 K +1 The ions of the salt bridge balance out the electrical potential that builds up, letting the electricity flow and flow!

16 bulb PbCl 2(AQ) Mg(OH) 2(AQ) Pb Mg Salt bridge NaCl (AQ) Completely label this, OX side, RED side, anode, cathode, direction of electrons, directions of salt ions, and think about the 3 reasons that this battery would (will) die.

17 bulb PbCl 2(AQ) Mg(OH) 2(AQ) Pb Mg Salt bridge NaCl (AQ) Write the half reactions where they belong, then the net ionic equation too. ½ ox: __________________________ ½ red: ______________________________ NET ionic equation: ______________________________________

18 bulb PbCl 2(AQ) Mg(OH) 2(AQ) Pb Mg Salt bridge NaCl (AQ) All voltaic cells die for the same three reasons


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