1. Solutions of Electrolytes
Electrochemistry

2. Electric Current Energy is released when electrons are transferred
This can be heat energy, or electric energy
Zn + CuSO4 example – heat energy
When separated by a barrier – electrical energy is produced

3. Electric Energy
By using a porous barrier to separate the reactants, electrons being exchanged between ions are forced to travel through a connecting wire, producing electricity
This type of set-up is called an electrochemical cell

4. Voltaic Cells
A voltaic cell is an electrochemical cell in which a spontaneous redox reacton produces a flow of electrons through an external circuit
A circuit is a closed loop path for current to flow
In the wire the negative electrons flow from anode to cathode

5. Parts of the Voltaic Cell
The voltaic cell is actually composed of two halves, each called a half-cell
Anode – the source of the electrons, it is the electrode at which oxidation occurs as electrons are lost by a substance
Cathode – accepts the electrons, it is the electrode at which reduction occurs as electrons are gained by a substance

6. Inner workings of the voltaic cell
Any element that loses electrons has undergone oxidation. This takes place at the anode
Any element that gains electrons has undergone reduction, this takes place at the cathode
Oxidation and reduction must occur together
Any reaction in which electrons are gained or lost in equal numbers is a redox reaction
Zn + Cu2+  Zn2+ + Cu

8. Redox in the voltaic cell
In the cell, redox reactions result in a continuous flow of electrons from anode to cathode
Assignment
1-5 page 580

9. Lab 1 Purpose: To create a chemical cell (voltaic cell)
To understand how a chemical cell works

10. Materials:
(2) 250 mL beakers
A paper towel
(1) copper electrode
(1) zinc electrode
Voltmeter (reading between 0 v and 1.5 v)
1M CuSO4
1M NaCl
1M ZnSO4

11. Procedure:
Attach the Zinc electrode to the negative (common) side of the voltmeter and the Copper electrode to the positive side of the voltmeter.
Pour the 1M CuSO4 solution into one 250 mL beaker.
Pour the 1M ZnSO4 solution into one 250 mL beaker.
Place the Zinc electrode in the ZnSO4 solution.
Place the Copper electrode in the CuSO4 solution.
Soak the paper towel in the NaCl solution and place one end each beaker.
Record the voltage that is created by the chemical cell.

13. Current
The activity series allows you to predict which ions are best at donating and accepting ions
Half-Reaction – the reaction occurring at each electrode
The amount of electric energy that can be generated by each half-reaction is determined by its reduction potential

14. Current
Standard Reduction Potential- The E0 of a half-cell connected to the standard hydrogen electrode when ion concentrations in the half-cells are 1 M, gases are at a pressure of 1 atm, and the temperature is 25 degrees C
E0 represents the voltages generated by half-reactions

15. SHE The standard hydrogen electrode (SHE) has the half-reaction
The concentration of hydrogen ion is 1 M, the temp is 25 degrees C, and the pressure of the hydrogen gas is 1 atm
Is considered the anode in each cell
If E0 is (+) it indicates that hydrogen is more willing to give up electrons than the metal
If E0 is (-) it indicates that the metal is more willing to give up electrons than hydrogen

16. The activity series
Ordering the potentials of the metals results in a table of reduction potentials
Pg 585 of your text

17. Calculating E0 E0 cell = E0 cathode - E0 anode
Example: calculate E0 for the zinc/copper cell
Zn2+ + 2e-  Zn E0 = V
Cu2+ + 2e-  Cu E0 = V
Reduction of Zn has a lower E0 so Zn is the anode
E0 for the cell is the difference between the two, V

18. Assignment
6-10 pg 586
Due tomorrow

19. Oxidation States
An Oxidation State (or oxidation number) is a numerical representation of an atoms share of the bonding electrons
In ionic compounds it is equal to the ionic charge
In covalent compounds it is the average charge assigned to an atom according to electronegativities

20. Rules for assigning ox states
A free element is 0
For an ion it is the ionic charge
The more electronegative element in a binary compound is assigned the number equal to the charge it would have if it were an ion
H is +1, unless it is combined with a metal, in which case it is –1
F is always –1, because it is the most electronegative element

21. Rules cont.
6. O is –2, unless combined with F (+2), or in a peroxide (-1)
7. Al has +1,2,or 3 in compounds, group 1 and group 2 respectively
8. The sum of all ox #’s in a compound is 0
9. The sum of all ox #’s in a polyatomic ion must = the charge of the ion

22. Redox and ox #’s Changes in oxidation #’s indicate a redox reaction
Any time a pure element appears as a reactant or product, you have a redox reaction
Oxidation numbers are used to balance redox reactions

23. Balancing Redox equations
OIL RIG
Oxidation Is Loss of electron
Reduction Is Gain of electron
The half-reaction method
See page 593 in text
Assignment
Problems page 594

24. How Batteries Work
Batteries use redox reactions to convert chemical energy into electrical
A battery is a single voltaic cell or group of voltaic cells that are connected together

25. When designing a battery:
Redox rxn must be spontaneous
Half-reactions must produce the desired voltage
If you want a rechargeable battery, the redox reaction must be easy to reverse
Environmental concerns must be addressed

26. Zinc-Carbon batteries
Most common battery
Also known as the dry cell battery
Uses reaction involving zinc and manganese dioxide
Zinc container is the anode
Carbon rod is the cathode

27. Alkaline batteries
Alkaline batteries are zinc-carbon batteries that use KOH instead of NH4Cl
Has no carbon post
Perform better than normal zinc-carbon batteries

28. Mercury Batteries Similar to the alkaline battery
HgO is reduced at the cathode
The production of liquid mercury is a major disadvantage for mercury batteries
Used mercury batteries must be recycled so that the elemental mercury can be recovered

29. Rechargeable Batteries
The process in which electric energy is used to drive a redox reaction is electrolysis
The container in which electric energy drives a nonspontaneous redox reaction is an electrolytic cell

30. Car Batteries Car batteries are lead-acid batteries Contains six cells
Produces 12V
Lead serves as the anode
The electrolytic solution is sulfuric acid (H2SO4)
The voltage produced from the cars alternator reverses the half reactions and regenerates Pb, recharging the battery

31. Ni-Cad batteries Are also rechargable Cadmium is the anode
NiO(OH) is reduced at the cathode
Must be recycled because of the toxicity of cadmium

32. Assignment
16-21 page 599

33. Electroplating
Electroplating is the deposition of a metallic coating onto an object by putting a negative charge onto the object and immersing it into a solution which contains a salt of the metal to be deposited. The metallic ions of the salt carry a positive charge and are attracted to the part. When they reach it, the negatively charged part provides the electrons to reduce the positively charged ions to metallic form.

34. Electroplating
example

35. Electroplating activity
Objective:Electroplate silver on to copper

36. Research Paper
Write a research paper on the development and use of rechargable batteries in LEV’s.
Format:
Must be typed, single spaced
Body must be 2-3 pages
Style: MLA
Worth a possible 25 points
Due Friday, Dec. 7

37. Electrochemical cells at nonstandard conditions
The Nernst Equation
E = E0 – V ln Q at 25˚ C n
Q = reaction quotient
n = number of moles of electrons transferred