Chapter 19Oxidation-Reduction Reactions Pg. 595

• Oxidation- valence electrons are lost• Reduction- valence electrons are gained• Rules for determining the oxidation number of

an element (pg. 595)• Practice assigning Oxidation numbers (pg. 612

#7 a-j) (pg.612 #6)

Oxidation-Reduction Reaction• Also called-Redox• Transfer of electrons• One cannot happen without the other.

Oxidation Reduction

Is Is

Losing GainingOxidation #increases Oxidation # decreases

Remember:Oil Rig

• Determine Oxidation or Reduction • (pg. 612 #4)• Pg. 599 #3 a. is an example. Try b-e on your

own for practice.• Practice Pg. 605 #1• Pg. 612 #2 a-i,3,5 a-c,17 a-e,18

Hon Chem Ch 20 Pg 655Electrochemical Cells

• AKA batteries • Pg 643 Zn is good reducing agent (gets

oxidized, loses electrons, ox# goes up)• Cu is good oxidizing agent (gets reduced, gains

electrons, ox# goes down)

Parts and Types of BatteriesPg 656-9

1. Zinc-Carbon Dry Cella. big, used in flashlights, C and D batteriesb. Zn container – anode, negative, becomes + as loses electronc. C rod in center – cathode, + bump on end

of battery, becomes negative as gains electrons

2. Alkaline Batteriesa. smaller, AA and AAA, cameras, remotes

b. Zn and KOH instead of Zn and C 3. Hg Batteries

a. tiny, hearing aids, watchesb. Zn, KOH, Steel, HgO

Corrosion and PreventionPg 661-2

• Fe is oxidized, loses electrons, forms rust• Salt and acid speed up the oxidation• Zn coating prevents oxidation due to Pg 643,

called galvanizing• Electric potential difference = volts (how hard

electricity pushes thru wire)

Recharging BatteriesPg 667-9

• Voltaic cell – battery making electricity, anode gives electrons to cathode

• Electrolytic cell – battery when being recharged, storing electricity, direct current source forces cathode to give electrons back to anode

• DC sources - wall charger with diode to change AC to DC, car alternator, other battery (jumping a car)

• Can be recharged as long as enough products to act as reactants to reverse reaction, corrosion is loss of products/reactants so can’t recharge after corroded Pg 669**do redox rxn for car battery