Unit 17: Oxidation-Reduction Reactions:   Electrochemistry

Reading
BJU book: Ch. 17 "Oxidation-Reduction" 

Topics
  • What is oxidation and reduction
  • Electrolytic cells 
  • Voltaic cells 
  • Practical applications

​Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. 
Here is a list of possible labs for this lesson. I will choose from this list when we get here. ​
  • ​The "Battery Build lab" is our regular lab, but there are numerous virtual labs which cover the topics well. There are also labs you can do at home. We'll decide when we get here. ​
Hands-on labs you could do at home with supervision:
  • You can easily build a battery at home. This is a great "oxidation-reduction" lab exercise. 
  • You can easily set up an 'electroplating' lab using copper and steel wool. This is fun too. 
  • You can easily "electrowin" dissolved copper from a synthetic wastewater sample. 
  • There is also a "corrosion" lab using steel nails in Agar, but is pretty involved. 
Virtual labs which pertain to the topics covered:
  • Good time to do one of the previous weblabs we missed. 
Below: A hydrogen fuel cell uses H2 gas and a cation-permeable membrane to generate electricity. Pure water is the only waste produced.
  • Advantages - a clean source of energy.
  • Disadvantages - you have to make the hydrogen, first! (which is expensive and difficult to store because its such a small molecule it leaks out of just about any container)
Lecture outline
Here we are really learning about electrochemistry. This is a field which is today making many *millionaires and billionaires* in the fields of batteries and alternative energy. Thus, it is a very modern and interesting topic...

Topics
  • ​Oxidation and Reduction (Redox) chemical reactions.
  • How to tell if a reaction is a Redox reaction.
  • Electrolytic cells. Electrolysis and plating.
  • Voltaic cells. Batteries.

Overview:
  • Chemical Reactions which involve the TRANSFER of electrons are called OXIDATION-REDUCTION reactions - or REDOX reactions.
  • The element which is OXIDIZED loses electrons. When you burn briquettes in your barbeque, for example, you OXIDIZE the charcoal (carbon) as follows: C + O2 = CO2.  In this reaction, the Carbon goes from a '0' formal charge to a '+4' formal charge. It is oxidized.
  • The element which is REDUCED gains electrons. In the reaction above, the Oxygen goes from a '0' formal charge to a '-2' formal charge. It is reduced.
  • You can use "OIL RIG" to help you remember. "Oxidation Is Loss; Reduction Is Gain" (of electrons)
  • Another mnemonic device is "LEO says GER", which means "Loss of Electrons is Oxidation; Gain of Electrons is Reduction".
  • The substance which is OXIDIZED (the carbon, above) is functioning as a REDUCING AGENT. This is because it reduces the other substance. Pure carbon is an excellent REDUCING AGENT, used in many chemical processes.
  • The substance which is REDUCED (the oxygen, above) is functioning as an OXIDIZING AGENT. This is because it oxidizes the other substance. Oxygen makes an excellent OXIDIZING AGENT. That is its chief role in nature, in fact.
  • It's important to realize that NOT ALL REACTIONS involve the transferal of electrons; for example, the common reaction HCl + NaOH = NaCl + HOH only shifts around the players - it doesn't change the formal charges on any of the atoms, and no atoms 'steal' electrons from the others. Each atom begins and ends with the same number of electrons, and with the same formal charge. Thus it is not a Redox-type reaction.
Practical applications:
  • With REDOX reactions, we can build batteries and energy-storage devices like FUEL CELLS and FLOW BATTERIES. We can ELECTROPLATE metals and other things; and we can drive a whole range of industrial processes which rely on the oxidation and reduction of materials.
  • Redox reactions are also really important when we study BIOCHEMISTRY and the processes of LIFE. Your body is fueled by oxidation/reduction reactions which occur in your cells.
  • With batteries and fuel cells, the substance being REDUCED is the FUEL. In a flashlight battery, zinc metal is the fuel. In a lithium battery, a compound of lithium is the fuel.
  • A BATTERY is nothing but a CHEMICAL REACTOR in which we force the electrons to go around a CIRCUIT and do USEFUL WORK before returning to the other terminal of the battery. That's all a battery and fuel cell really are! We will discuss...
Electrochemistry lab
We will make and test voltaic cells (batteries).
We will make LeClanche Cells from scratch and hook several cells up in series to create a higher voltage and power something useful.
  • The history of battery-development is very interesting! 
  • The LeClanche Cell was a big improvement over the earlier "wet" cells, like the Daniell Cell, which could tip over and spill acid all over your telegraph station! 
  • The LeClanche Cell used *dry ingredients*, and became known as the "dry cell". 
  • With the "dry cell" you could now have a hand-held flashlight, for example! And you didn't have to worry about hydrogen gas (and acid spilling) in your telegraph office. 

Homework - check your class emails for due dates
Will be posted here