Unit 17: Oxidation-Reduction Reactions: Electrochemistry
Reading
BJU book: Ch. 17 "Oxidation-Reduction"
AP Classroom: Unit 9 "Applications of Thermodynamics"
Topics
Lab
BJU book: Ch. 17 "Oxidation-Reduction"
AP Classroom: Unit 9 "Applications of Thermodynamics"
Topics
- Learning oxidation and reduction reactions
- Electrolytic cells (includes things like electroplating, electrolysis, and electrowinning)
- Voltaic cells (batteries and fuel cells)
Lab
- Battery-Build lab
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*
Overview:
Here we are really learning about electrochemistry. This is a field which is today making many *millionaires and billionaires*
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. 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. Oxygen makes an excellent OXIDIZING AGENT.
- It's important to realize that NOT ALL REACTIONS involve the transferral of electrons; for example, the common reaction HCl + NaOH = NaCl + HOH only shifts around the atoms - it doesn't change the formal charges on any of them, 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.
- Biochemistry: Your body is fueled by oxidation/reduction reactions which occur in your cells.
- A BATTERY is nothing but a CHEMICAL REACTOR in which we force the electrons to go around a CIRCUIT and power a laptop computer before returning to the other terminal of the battery.
Battery-Build lab
If you've never built a battery from scratch, you'll find it's an interesting project. The two 'classic' chemistry-lab batteries are:
If you've never built a battery from scratch, you'll find it's an interesting project. The two 'classic' chemistry-lab batteries are:
- the Daniell Cell (harder)
- the LeClanche Cell (easier)