chapter 20

oxidation and reduction

another way to balance reactions, or another way to look at what happens during a reaction.

reactions are an exchange of electrons. some atoms lose, some atoms gain.

reduction - is the gaining of electrons ( -)oxidation - is the losing of electrons ( becoming more +)

reducing agent- cause another atom to be reduced by donating electrons

oxidizing agent- often oxygen, it is the atom that takes electrons and causes another atom to lose them.see pg 156 for rules

see the chart on page 156 for rules about oxidation numbersyou need these so you can tell if you are gaining or losing electrons

now try them in a reaction

H2 + O2 = H2O

Na + SO4 -

o-2cl-

Mn+3

try some!KClO3

H2OUF6

MnO4

last element treat as an ion ( or 1st if need be)

balance 1st so total is zero

if polyatomic ion, balance to charge

element = oion = chargeoxygen = -2hydrogen =1flourine =-1

try some!Mg +2

KClO3

H2O

Cl2 (g)

UF6

MnO4

+2

+1, +5, -2

+1, -20

+6 -1

+8, -2

3 ways to look at oxidation-

remember that originally oxidation always meant where oxygen had been added, like the creation of rust or tarnishing of silver

Fe + O2 2Fe2O3

figure oxidation states, see what the job of the oxygen is?

so oxidation means to add oxygenit also means to lose electronsit is also the increase of oxidation number!!!

it is a good idea to know the chart next page for some common oxidizing and reducing agents!!!

try pg 922 1-11

+

oxidizing agentreduction agent

O2, Halogens F, Cl,IC2O7

-2

MnO4

-

H2, metals, C

quiz over oxidation/reduction numbers

For the following reactions, assign oxidation numbers, then list the oxidizing agent

1. KClO3 KCl + O2

2. H2 + I2 HI

3. Cu + AgNO3 Ag + CuNO3

what types of reactions are redox reactions?

synthesis and decomp.

that should make sense since there are elements either as reactants or products

single replacement reactions-

when you have an element and a compound, and the element becomes part of the product compound, oxidation states have altered.

remember net ionic equations? write it out, seperate the ionic compounds, get rid of everything that doesn't change. that is great for redox, cause you can look at just the exchange of electrons

AgNO3 + Cu s CuNO3 + Ags

better yet Ag + + Cus Cu+ + Ags

activity series

this is a list of metals in order of most reactive to least reactive. it will also help you figure out how a single replacementreaction should occur. good for oxidation reduction cause that is what most are!KCa react with waterNaMgAlSnFe react with acidNiSn PbH2

CuHg very unreactiveAgAu

at the same time the list of halogens is just top to bottom of the periodic table.

F can replace all I replaces nothing.

so can the following occur?

Na + Ca(OH)2 Mg + H20?Mg + HCl?