1. Electrochemistry Is the study of the interchange of chemical and electrical energy HW: Read CH 8 and 18 3 min https://www.youtube.com/watch?v=GhbuhT1GDpIhttps://www.youtube.com/watch?v=GhbuhT1GDpI

2. Oxidation and Reduction reactions (REDOX) Assigning Oxidation Number rules (you probably have most of this figured out). The point is to keep track of electrons. 1)Free element is 0 2)Oxygen is -2 (usually), Aluminum is +3 3)Group 1 metals is +1 4)Group 2 metals is +2 5)More electronegative element in a compound is assigned charge if it were an ion (Halogens are usually -1) 6)Neutral compound all numbers add to 0 7)Polyatomic ion all numbers add to ion charge *Assign charge where known and then solve for unknown*

3. Oxidation and Reduction reactions (REDOX) What is the oxidation number of Se in HSeO 3 - ? HSeO 3 - +1 + x + (-2)3 = -1 x = +4 You could think of it like an algebra problem (subscript = multiply by)1(+1) + 1(x) + 3(-2) = -1

4. Oxidation and Reduction reactions (REDOX) YOU TRY! What is the oxidation number? A) Sulfur in SO 3 B) Manganese in MnO 4 - C) Cobalt in [CoCl 6 ] 3-

5. Oxidation and Reduction reactions (REDOX) Think of ionic compounds between metals and nonmetals Oxidation Is a Loss of electrons (so charge is positive) K  K + + e - (potassium is oxidized) Reduction Is a Gain of electrons (so charge is negative) Cl 2 + 2e -  2Cl - (Chlorine is reduced) OIL RIG Movement of electrons = energy

6. Which is getting oxidized? Reduced? (not balanced equations) Zn + Cu 2+  Zn 2+ + Cu H 2 + O 2  H 2 O Ag(NO 3 ) + Cu  Cu(NO 3 ) 2 + Ag

7. Oxidation and Reduction reactions (REDOX) Write 2 half-reactions (oxidation and reduction). 1) write equation for reaction 2) assign oxidation numbers to all atoms 3) identify who is getting oxidized/reduced 4) divide reaction into 2 half reactions and balance separately (ADD electrons)

8. Oxidation and Reduction reactions (REDOX) Write 2 half reactions for Zn(s)+ Cu(SO 4 )(aq) → Zn(SO 4 )(aq) + Cu(s) 0+2 -2 +2 -2 0 Oxidation: Zn 0  Zn 2+ + 2e - Reduction: Cu 2+ + 2e -  Cu 0

9. Oxidation and Reduction reactions (REDOX) Write 2 half reactions for Na + Cl 2  NaCl 0 0 +1 -1 Oxidation: Na 0  Na + + e - Reduction: Cl 2 0 + e -  Cl -

10. Oxidation and Reduction reactions (REDOX) YOU TRY! Identify what is getting oxidized and reduced and write their half-reactions Mg + O 2  MgO Reduction: Oxidation: MnO 4 -1 + Br -1  MnO 2 + BrO 3 -1 Reduction: Oxidation:

11. Electrochemistry Involves TWO MAIN TYPES Of Electrochemical Cells: Galvanic (voltaic) cells – generates useful electrical energy (battery; frequently used in power plants) Electrolytic cells –require external energy source (a direct current or DC power source like a flashlight battery) * you can vary the materials to produce different batteries (alkaline, lithium, mercury) that in turn produce different energy (lots energy that slowly decreases vs. less energy but longer life span) How its made 5 min https://www.youtube.com/watch?v=ksxSOwA933Mhttps://www.youtube.com/watch?v=ksxSOwA933M

13. Galvanic Cell “anatomy” Anode – Electrode where oxidation occurs. Negative end. (anode may appear to become smaller as it falls into solution) Cathode – Electrode where reduction occurs. Positive end. (it may appear larger, due to ions from solution plating onto it) Salt bridge – used to maintain electrical neutrality in a galvanic cell Electron flow – ALWAYS through the wire from anode to cathode Voltmeter – measures the cell potential in volts

14. Galvanic Cell pneumonic devices AN OX – oxidation occurs at the anode (may show mass decrease) RED CAT – reduction occurs at the cathode (may show mass increase) FAT CAT – The electrons in a voltaic or galvanic cell ALWAYS flow F rom the A node T o the CAT hode ca+hode

15. Galvanic Cell Write 2 half reactions for the following reaction. Then fill in the Galvanic cell. (answer on next slide) Zn + Cu 2+ → Zn 2+ + Cu https://www.youtube.com/watch?v=SO7VLy2BoU8 (5 min) https://www.youtube.com/watch?v=SO7VLy2BoU8

16. And the answer is… RED: Cu 2+ + 2e- → Cu OX: Zn → Zn 2+ + 2e-

17. Can you try on your own?? Write 2 half reactions for the following reaction. Then fill in the Galvanic cell. HINT: NO 3 is not in the reaction. Cu + H(NO 3 ) --> Cu(NO 3 ) + H 2

18. Electrolytic Cell Electrolytic cells are forced to occur by using an electron pump or battery or any type of DC source A galvanic cell is separated into two half cells to generate electricity; an electrolytic cell occurs in a single container. A galvanic cell IS a battery, an electrolytic cell NEEDS a battery

19. Electrolytic Cell

21. Classifying REDOX reactions Synthesis (combination): 2 or more reactants come together to form one product Decomposition: 1 compound breaks down into 2 or more smaller compounds

22. Classifying REDOX reactions Single displacement (replacement): An uncombined element switches with another element in a compound Double displacement (replacement): 2 compounds “switch partners” with each other Combustion: involves oxygen as one of the reactants that produces carbon dioxide and water

24. YOU TRY! Balance the following equations and indicate the type of reaction taking place A) NaBr + H 3 PO 4  Na 3 PO 4 + HBr B) H 2 O + SO 3  H 2 SO 4 C)As + Cl 2  AsCl 3