Unit 1 Electrochemistry

Oxidation

Loss of electrons

Reduction

Gain of electrons

Oxidizing Agent

• The compound/ element that causes ANOTHER element to be oxidized (to lose electrons)

• Gains the electrons lost by what is oxidized

• The reduced species

Reduction Agent

• The species that causes ANOTHER specie to be reduced (to gain electrons)

• Loses the electrons that are then gained by the other species

• The oxidized species

What are the three types of batteries?

• Primary Cell

• Secondary Cell

• Flow/ Fuel Cell

What are the types of primary cells?

• Lelanche (dry) Cell

• Button Battery/ Silver-Zinc Cell

What are the characteristics of primary cells?

IRREVERSIBLE cell reactions — Battery will eventually go dead

What are the characteristics of Lelanche/ Dry Cells?

• Zinc is usually the anode due to not corroding rapidly

• Cathode: Manganese oxide (MnO2), Sometimes Mercury

• Voltage V = 1.5 V

• Corrosion = battery shell falls apart = manganese oxide paste leaks out

What are the types of Lelanche/ Dry Cells, and their characteristics?

• Hold charge for a long time, good for emergency use

• Acidic Battery

  • Zinc anode

  • Ammonium + manganese dioxide cathode forming manganese oxide, ammonium, and water

• Alkaline Battery

  • Zinc + hydroxide anode forming zinc oxide and water

  • Manganese dioxide cathode forming manganese oxide and hydroxide

What are the characteristics of Button Battery/ Silver-Zinc Cells?

• Very small in size, high storage capacity

• Voltage potential = 1.8 V

• Alkaline Cell

• Zinc + hydroxide anode forming zinc oxide and water

• Silver oxide and water cathode forming silver and hydroxide

What are some examples of Lelanche/ Dry Cells?

• AA, AAA, 9V, etc. batteries

What are some examples of uses of Button Batteries?

• Watches

• Hearing aids

• Some cameras

What are some characteristics of Secondary Cells?

• Rechargeable type of battery — Cell reaction can be reversed by passing electricity through the cell

• Battery can be used over several hundred cycles

What types of Secondary Cells are there?

• Lead-Acid/ Storage Battery

• NiCad (Nickel-Cadmium) Battery

• Lithium Battery/ Li-Ion Cell

Characteristics of Lead-Acid/ Storage Batteries

• Anode: Lead and hydrogen sulfate form lead sulfate and hydrogen ions

• Cathode: Lead oxide ad hydrogen sulfate and hydrogen ions form lead sulfate and water

What are examples of Lead-Acid/ Storage batteries?

• Car batteries

  • 35% sulfuric acid by mass, in which the density changes with battery life

  • Can function for several years, but will eventually fail due to reactions within the battery

  • Can be jumped to recharged them (but dangerous)

What are the characteristics of NiCad Batteries?

• Home-use and rechargeable versions of dry cell batteries

• Sometimes found in cordless electronic devices

• Batteries “remember” their common discharge percent, leads to decrease in capacity

• Deep discharge (usage until 0 battery life before recharging) recommended

• Alkaline cell

What are characteristics of Lithium batteries?

• Few year lifetime

• Found in common electronics: Smartphones, E-cars, laptops, camcorders, etc

• Heat is not good for it

• Perform best at a high charge

What are characteristics of Flow/ Fuel cells

• Reactants, products, electrolytes pass through a converter of chemical —> electrical enery

• Two types: Fuel cells andAir batteries

  • Fuel cells are used for very big projects: power plants, mechanical electric generators, space programs, etc

Corrosion

• The process of returning a metal into its natural ore state

• Basically the metal gets oxidized (think iron rusting = iron oxidizing)

• Gold (Au) is the only metal that shows no corrosion when in contact with air

Cathode protection

• Technique used to control the corrosion process of a metal

• Sacrificial anode attached to metal, and will oxidize/ corrode before the metal it’s protecting

Plating

• The technique of adding a sacrificial anode onto another metal

• Method of cathode protection

• Commonly Cr, Sn, and Zn

Alloy

• Mixture of metals

• May or may not be homogenous

Electrolysis

• Process of making non-spontaneous reactions happen via electricity or a battery

• Can be used to figure out which metals will “plate out” (oxidize) first

Electrorefining

• Deposition (depositing) of a pure metal at a cathode from a solution

Electroplating

• One metal is plated on another

• Less expensive than electrorefining