oxidation and reduction
DESCRIPTION
Oxidation and Reduction. ………………………. Objectives. Oxidised, reduced Definition- oxidising/reducing agent, oxidant/reductant Rules of oxidation number Refer to oxidation number and decide-reduced or oxidised. Redox Reactions. = reactions involving RED uction and OX idation. Reduction. - PowerPoint PPT PresentationTRANSCRIPT
Oxidation and Reduction
……………………….
Objectives
• Oxidised, reduced
• Definition- oxidising/reducing agent, oxidant/reductant
• Rules of oxidation number
• Refer to oxidation number and decide-reduced or oxidised
Redox Reactions.
Oxidation
Reduction
= reactions involving REDuction and OXidation
Overview
• Oxidation and reduction reactions always occur simultaneously (redox reactions)
3 ways of looking at oxidation and reduction
• 1. oxidation is a gain of oxygen atoms, reduction is a loss of oxygen atoms
• 2. oxidation is a loss of hydrogen atoms, reduction is a gain of hydrogen atoms
• 3. oxidation is a loss of electrons, reduction is a gain of electrons– Most fundamental explanation, what we will
be dealing with the most
Oxidation Reduction
Gains oxygen Lose Oxygen
Lose Hydrogen Gains hydrogen
Lose Electrons Gains electrons
Oxygen
Hydrogen
e-
OXIDATIONOXIDATION REDUCTIONREDUCTION
= OXYGEN= OXYGEN
= HYDROGEN= HYDROGEN
= ELECTRON= ELECTRON
= OXIDATION STATE= OXIDATION STATE
REDOX REACTIONS
Definitions:
GAINGAIN LOSSLOSS
LOSSLOSS GAINGAIN
LOSSLOSS GAINGAIN
INCREASEINCREASE DECREASEDECREASE
Remember “OILRIG” : Oxidation Is Loss ; Reduction Is Gain (of electrons)
Oxidation states (also called oxidation numbers) are numbers assigned to EACH ATOM that takes part in a reaction.
Oxidation states are assigned using a set of International rules.
Redox-loss or gain of Oxygen
• Remember that reduction is a loss of oxygen from a compound
• We converted iron ore to metallic iron– We removed oxygen from the iron(III) oxide
– 2Fe2O3 + 3C 4Fe + 3CO2
– Carbon was oxidized because it gained an oxygen
Oxidizing and Reducing Agents
• Now the confusing part…
• CuO + H2 Cu + H2O
• Cu goes from +2 to 0– Cu is reduced, therefore it is called an oxidizing
agent (OXIDANT) because it causes some other substance to be oxidized
• H goes from 0 to +1– H is oxidized, therefore it is called a reducing agent
(REDUCTANT)because it causes some other substance to be reduced.
Identifying Agents in an Equation
• CuO + H2 Cu + H2O
Reduction: CuO is the oxidizing agent
Oxidation: H2 is the reducing agent
Examples
• Is the reactant oxidized or reduced?
• Pb PbO3
• SnO2 SnO
• KClO3 KCl
• C2H6O C2H4O
• C2H2 C2H6
Leo the Lion!
• LEO the lion says GER– Loss of electrons is oxidation, gain of
electrons is reduction
Pertaining to LEO…
• Mg + S MgS• Mg + S Mg2+ + S2-
• Magnesium is oxidized– Said to be the reducing agent– Substance in the reaction that loses electrons
• Sulfide sulfur atom is reduced – Said to be the oxidizing agent– Substance in the reaction that gains electrons
Oxidation Numbers
• A count of the electrons transferred or shared in the formation or breaking of chemical bonds
• To see if electron is lost or gained in the reaction an oxidation number is assigned to each element
• Follow a set of rules to assign oxidation number…
Rules for deciding Oxidation States (Numbers) :
5. In a BINARY (2 elements) COMPOUND
1. In all UNCOMBINED ELEMENTS, atom’s ox. no. = 0 .
2. In all COMPOUNDS, sum of ox. no.’s equals zero.
3. In all IONS, sum of ox. no.’s equals ion charge.
4. In all COMPOUNDS : Gp 1 elements + 1
+ 2
- 1
+ 3
the more electronegative atom given NEGATIVE ox. no. and the less electronegative atom given POSITIVE ox. no.
In most COMPOUNDS,
6. H = + 1 except when bonded to a metal- metal must have the positive ox. no.
7. O = - 2 except when bonded to F or in peroxides, e.g. Na2O2- F must have the negative ox. no. )
LEA
RN
and PR
AC
TIS
E
Gp 2 elements
Gp 3 elementsFluorine
Oxidation NumbersOxidation Numbers
• The oxidation numbers of atoms in a compound add up to zero.
F -1
O -2
H +1
Cl -1
Find the oxidation state of C in CO2?
? – 4 = 0
? = +4Put the +!
Oxidation NumbersOxidation Numbers• The oxidation
numbers of atoms in an ion add up to the charge on the ion.
F -1
O -2
H +1
Cl -1
Oxidation state of S in SO4
2-?
? – 8 = -2
S = +6
ASSIGN AN OXIDATION NUMBER / STATE TO EACH ATOM IN :
Cl2 CO32-
Ca2+ SO32-
Al3+ ClO-
H2O IO4-
CO2 CH4
ClF MnO4-
NO3- Na2S4O6
CuCl CuBr2
N2 C2O4
2-
BrF5 Mn2O3
SF6 CO
S2- BrF
VCl2 Na2S
NO2- BrO3
-
NH4+ H2SO4
SO42- I-
S2O32- NH3
CCl4 Cr2O7
2-
Cl(0)
Ca(+2)
Al(+3)
H(+1) O(-2)
O(-2) C(+4)
F(-1) Cl(+1)
O(-2) N(+5)
Cl(-1) Cu(+1)
N(0)
F(-1) Br(+5)
F(-1) S(+6)
S(-2)
Cl(-1) V(+2)
O(-2) N(+3)
H(+1) N(-3)
O(-2) S(+6)
O(-2) S(+2)
Cl(-1) C(+4)
O(-2) C(+4)
O(-2) S(+4)
O(-2) Cl(+1)
O(-2) I(+7)
H(+1) C(-4)
O(-2) Mn(+7)
Na(+1) & O(-2) S(+2.5)
Br(-1) Cu(+2)
O(-2) C(+3)
O(-2) Mn(+3)
O(-2) C(+2)
F(-1) Br(+1)
Na(+1) S(-2)
O(-2) Br(+5)
O(-2) & H(+1) S(+6)
I(-1)
H(+1) N(-3)
O(-2) Cr(+6)
Problems
• What is the oxidation number of each element?
• I2
• Cr2O3
• AlCl3• Na2SO4
• CaH2
Identifying Redox Reactions using oxidation number
0 +3 -2 0 +3 -2
• 2 Al + Fe2O3 2 Fe + Al2O3
• Al increases from 0 to +3, it is Oxidized!
• Fe decreases from +3 to 0, it is Reduced!
Problems
• Zn Zn2+
• Fe3+ Fe2+
• CaCO3 CaO + CO2
• AgNO3 Ag
• Do Practice Exercises
Rem. OXIDATION REDUCTION
= OXIDATION No. INCREASE DECREASE
Work out the oxidation number change for each of the following process and use it to decide whether it is an OXIDATION or a REDUCTION.
PROCESS PROCESS Ox. No.’s Ox. No.’s OxidationOxidation ReductionReduction
ClCl2 2 Cl Cl--
CaCa Ca Ca2+2+
NONO2 2 NO NO
33--
MnOMnO44- - Mn Mn2+2+
SOSO22 SO SO
442-2-
IOIO44- - I I
22
HH22SOSO4 4 S S2-2-
BrBr2 2 BrO BrO--
NHNH44+ + NH NH
33
CrCr22OO77
2- 2- Cr Cr3+3+
Cl(0) (-1)
Ca(0) (+2)
N(+4) (+5)
Mn(+7) (+2)
S(+4) (+6)
I(+7) (0)
S(+6) (-2)
Br(0) (+1)
N(-3) (-3)
Cr(+6) (+3)
NONE