Oxidation Oxidation Reduction Reduction ReactionsReactions

Re-dox ReactionsRe-dox Reactions

Oxidation is the loss of electronsOxidation is the loss of electrons Reduction is a gain of electronsReduction is a gain of electrons

Leo goes Grr!Leo goes Grr! Lose Electrons OxidationLose Electrons Oxidation Gain electrons ReduceGain electrons Reduce

““Redox Reactions”Redox Reactions”

Many reactions involve (or seem to Many reactions involve (or seem to involve) a transfer of electrons.involve) a transfer of electrons.

Such reactions always involve both: Such reactions always involve both: Oxidation Oxidation Loss of electrons Loss of electrons

Na Na Na Na++ + e + e--

ReductionReduction Gain of electronsGain of electronsCl + eCl + e-- Cl Cl--

Determine a Redox Determine a Redox ReactionReaction

To determine if what you have is a redox To determine if what you have is a redox reaction, first rewrite the equation to reaction, first rewrite the equation to include the oxidation number for each include the oxidation number for each elementelement

The oxidation number is the charge an The oxidation number is the charge an element has or appears to have when element has or appears to have when combining to form compoundscombining to form compounds

Oxidizing/Reducing AgentsOxidizing/Reducing Agents

1.1. The element that was oxidized is part of the The element that was oxidized is part of the reducing agent.reducing agent.

2.2. The element that was reduced is part of the The element that was reduced is part of the oxidizing agent.oxidizing agent.

Assigning Oxidation Assigning Oxidation NumbersNumbers

1.1. All pure elements and homogeneous molecules = 0All pure elements and homogeneous molecules = 02.2. Elements in group IA = +1Elements in group IA = +13.3. Elements in group IIA = +2Elements in group IIA = +24.4. AgAg++, Zn, Zn+2+2, Al, Al+3 +3 (unless it is a pure metal) (unless it is a pure metal)5.5. In binary compounds the second element = anion In binary compounds the second element = anion

chargecharge

6.6. Oxygen is almost always = -2 *unless it is OOxygen is almost always = -2 *unless it is O22(g)(g)

7.7. Hydrogen is almost always = +1 *unless it is HHydrogen is almost always = +1 *unless it is H22(g)(g)

8.8. The total charge of a compound is always = 0The total charge of a compound is always = 0

A Sample ProblemA Sample Problem

What are the oxidation numbers of the What are the oxidation numbers of the elements in elements in NaNa22SOSO44??

Na = +1 (times 2 atoms) = +2

O = -2 (times 4 atoms) = -8

+2 + -8 = -6

If the compound must = 0, then S must = +6

Give the oxidation number for: Give the oxidation number for:

1.1. SS in Nain Na22SOSO33

2.2. Mn Mn in KMnOin KMnO44

3.3. NN in Ca(NOin Ca(NO33))22

4.4. CC in Nain Na22COCO33

5.5. NN in NOin NO22--

6.6. SS in SOin SO44-2-2

7.7. SS in Hin H22SS22OO77

8.8. FeFe in Fe(Cin Fe(C22HH33OO22))22

+4

+7

+5

+4

+3

+6

+6

+2

Ammonia plus OxygenAmmonia plus Oxygen

NHNH33 + O + O22 NO + H NO + H22OO

Is this equation balanced?Is this equation balanced? No, it does not matterNo, it does not matter

Step 1: Rewrite the equation with the Step 1: Rewrite the equation with the chargescharges

NN3-3-HH++33 + O + O00

22 N N2+2+OO2- 2- + H+ H++22OO2-2-

Ammonia plus OxygenAmmonia plus Oxygen

Step 2: Determine the changes in the Step 2: Determine the changes in the charges of each elementcharges of each element

NN3-3-HH++33 + O + O00

22 N N2+2+OO2- 2- + H+ H++22OO2-2-

Nitrogen changes from 3- to 2+Nitrogen changes from 3- to 2+ it lost an electron and was oxidizedit lost an electron and was oxidized

Oxygen changes from 0 to 2-Oxygen changes from 0 to 2- it gains electrons and so is reducedit gains electrons and so is reduced

Last StepLast Step

Step 3: If there is a species oxidized and Step 3: If there is a species oxidized and one reduced, then it is a redox equationone reduced, then it is a redox equation