JUST REMEMBER . . .

“OIL RIG”(oxidation is losing, reduction

is gaining)

REDOXIn a REDOX reaction, when

something is being oxidized, it is called the reducing agent, and when something is being reduced it is called the oxidizing agent

Oxidation StatesOxidation States are assigned to atoms to

identify how many electrons are either gained or lost by an atom

For example metals in Group 2 (like Ca) have a +2 oxidation state. Therefore Metals in Group 2 lose two electrons when they form compounds

Changes in oxidation numbers indicate that a redox reaction has occurred.

It is important to learn the rules for assigning oxidation states to atoms in order to determine whether oxidation or reduction has occurred.

Oxidation State Rules1) Free elements (not combined

with any other element) have an oxidation number of zero. Ex: Na, O2, H2

2) All metals in Group 1 have an oxidation number of +1.

3) All metals in Group 2 have an oxidation number of +2.

4) F (fluorine) always has an oxidation of -1

5) The oxidation of simple ions is equal to the charge on the ion. Ex: Mg+2 has an oxidation number of +2.

6) The sum of the oxidation numbers must equal 0 Examples: NaCl & MgCl2

7) In polyatomic ions, the sum of the oxidation numbers of all the atoms must equal the charge of the ion. Example: sulfate ion SO4

-2 .

8) In general, oxygen has an oxidation number of -2. Oxygen has an oxidation number of -1 in peroxides (O2

-2) Example: H2O2. Oxygen has an oxidation number of +2 in compounds with fluorine Example: OF2

9) Hydrogen has an oxidation number of +1 in all compounds combined with a non-metal. Hydrogen has an oxidation number of -1 when it is a metal hydrides (metal and hydrogen. Example: LiH, and CaH2

Assigning Oxidation Numbers

Dr. McGuiness’ “bookend” technique to assigning oxidation numbers to compounds with more than two elements.

1. Identify the oxidation # of the last element (overall charge)

2. Identify the oxidation # of the first element (overall charge)

3. If there is no charge to the compound, then the overall charge must be 0, therefore you can determine the oxidation # of the element in the middle.

Li(MnO4)

(+1) + (?) + (-8) = 0

-2 x 4 = -8

+1 x 1 = +1

Half-ReactionsExample:

Cu + Ag(NO3) → Cu(NO3)2 + Ag

1. Assign oxidation numbers to everything2. See which oxidation numbers change from

reactant side to product side.3. Determine which half-reaction is oxidation

(loses e-), and which is reduction (gains e-)

OX: Cu0 → Cu2+ + 2e-

RED: Ag+ + 1e- → Ag0

Balancing REDOX reactions

Cu + 2Ag(NO3) → Cu(NO3)2 + 2Ag

OX: Cu0 → Cu2+ + 2e-

RED: 2(Ag+ + 1e- → Ag) 2Ag+ + 2e- 2Ag0

When copper is oxidized, it loses 2 electrons, which are gained by the silver ion.

Copper = reducing agentSilver = oxidizing agent

Activity Series – Table JTable J compares how active

each metal and nonmetal is.

Metals higher up are more active, and replace metals from below them from compounds (remember single replacement???)

In a single replacement, the free element has to be more reactive than the element in compound in order for the reaction to be spontaneous.

If it isn’t – the reaction does NOT GO!!

Electrochemical CellsThere are two types of electrochemical cells,

Voltaic & Electrolytic

These cells rely on REDOX reaction in different ways to either generate energy or to separate elements in compound that would normally not exist on their own in nature.

Voltaic ElectrolyticSpontaneousChemical Electrical

EnergyAnode – oxidation (-)Cathode – reduction (+)Example: BATTERYElectrons travel from anode

to cathode (wire)More reactive metal

ALWAYS the site of oxidation

Salt bridge is for the flow of ions from one half-cell to another

Non-spontaneousElectrical Chemical Requires a battery as a

source of energyAnode – oxidation (+)Cathode – reduction (-)(+) charged ion moves

toward the cathode(-) charged ion moves

toward the anode

“RED CAT” “AN OX”

ElectroplatingAnother example of an

electrolytic cell.The process of

electroplating requires a layer of metal such as silver or copper, coating or covering any object to be plated (spoon or fork)

The item being plated is the cathode - reduction/(-)

The electrode must be the same metal that you are plating the object in.

Cathode (-)