Cell potential is related to concentrations Electrodes can be used that are sensitive to specific ions They measure concentrations of specific ions which can have an effect on the cell potential Ion-Selective Electrodes

Batteries Groups of galvanic cells connected which add together to give the total battery potential Different types…

Lead Storage Battery Used in cars Lead = anode Lead coated with lead dioxide = cathode Electrodes are dipped in sulfuric acid

Dry Cell Batteries Calculators, electronic games, digital watches, portable audio players, etc. Acid version, alkaline version, silver cell, mercury cell, etc.

Fuel Cells Reactant constantly supplied to a galvanic cell Reaction is: 2H 2(g) + O 2(g)  2H 2 O (l)

Corrosion Metals corrode because they oxidize easily (spontaneously) –The metals’ reduction potentials are less positive than oxygen gas –When half reactions are combined, there is a positive E° value –Speed of oxidation varies –Some metals form a thin protective oxide coating, preventing further erosion

Iron Corrosion Steel corrosion must be prevented b/c it makes the backbone of most of our buildings, bridges, and cars Chemical composition of steel is not uniform –Places where iron is easily oxidized/reduced Ions and electrons migrate via moisture on steel’s surface, causing rust Moisture acts as a salt bridge between the anode/cathode regions

Corrosion Prevention A coating (paint/metal plating) is applied to protect the metal from oxygen and moisture –Chromium/tin used to plate steel with an oxide coating –Zinc used in galvanizing steel forms an oxide- carbonate coating. Oxygen reacts with the zinc (sacrificial coating) instead of the metal underneath Alloying: covers metals with a thin layer of stainless steel or other desirable alloy

More Corrosion Protection… Cathodic protection: for buried tanks/pipes attaches an active metal (like Mg) loses electrons, keeping iron from oxidizing –Ships’ hulls work this way: bars of titanium attached to the steel hull keep the hull from being oxidized

Electrolysis Electrolytic cells use electrical energy to produce a chemical change (requires energy) –Electrolysis forces a current through a cell to produce a chemical change for which the cell potential is negative –Causes a nonspontaneous rxn to occur Charges batteries, produces aluminum metal, plates objects with chrome Switches the anode/cathode, flows in the opposite direction as the galvanic cell

Stoichiometry in Electrochemistry Can measure how much chemical change occurs with the flow of a given current for a specific amount of time We add current and time to the chemical equation and can use the mole to mole ratio to do problems Important Conversion Factor for Ampere (amp): 1 A = coulomb/second 1 Faraday: 1 mole e - = 96,486 C

Stoichiometry Example How many grams of copper can be reduced by applying a 3.00 A current for 16.2 min to a solution containing Cu 2+ ions? Answer: 0.96 g Cu

Plating Order Plating means depositing neutral metal on the electrode by reducing the metal ions in solution More positive (higher) E° value will plate out quickest Ex: pg. 851

Electrolysis Used Commercially… Production of Aluminum Electrorefining of Metals Metal Plating Electrolysis of Sodium Chloride

Production of Aluminum Aluminum used to not be able to be produced by humans (very expensive) Hall-Heroult process uses molten cryolite (Na 3 AlF 6 ) as a solvent for aluminum oxide Made aluminum easy (cheap) to produce Production of Al uses 5% of the total electricity used in the U.S.

Electrorefining of Metals Purifies metals like Cu, Fe, Zn, Ag, Au, Pt

Metal Plating Metals that corrode easily can be plated with a thin coating of a metal that is less likely to corrode Ex: “tin” cans = steel cans with thin tin coating, bumpers in cars are steel coated in chrome Object needing coating serves as the cathode in ions of the coating metal

Electrolysis of Sodium Chloride How sodium metal is primarily produced NaCl mixed with CaCl 2 to lower mp Downs cell used for electrolysis Pg. 856