IB topic 9 Oxidation-reduction Define oxidation and reduction in terms of electron loss and gain.
2016 topic 0 - oxidation and reduction (INTRODUCTION)
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Transcript of 2016 topic 0 - oxidation and reduction (INTRODUCTION)
IB Chemistry Power Points
Topic 09
Oxidation and Reduction
www.pedagogics.ca
REDOXA guide for A level students
KNOCKHARDY PUBLISHING2008
SPECIFICATIONS
Much taken from
OXIDATION
OXIDATION & REDUCTION – Simplified Definitions
OXIDATIONis a GAIN OF OXYGEN
2Mg + O2 ——> 2MgO
magnesium has been oxidised as it has gained oxygen
OXIDATION & REDUCTION – Simplified Definitions
OXIDATIONis a GAIN OF OXYGEN
2Mg + O2 ——> 2MgO
magnesium has been oxidised as it has gained oxygen
is the REMOVAL (LOSS) OF HYDROGEN
C2H5OH ——> CH3CHO + H2
ethanol has been oxidised as it has ‘lost’ hydrogen
OXIDATION & REDUCTION – Simplified Definitions
OXIDATION & REDUCTION – Simplified Definitions
REDUCTION
OXIDATION & REDUCTION – Simplified Definitions
REDUCTIONis a GAIN OF HYDROGEN
C2H4 + H2 ——> C2H6
ethene has been reduced as it has gained hydrogen
OXIDATION & REDUCTION – Simplified Definitions
REDUCTIONis a GAIN OF HYDROGEN
C2H4 + H2 ——> C2H6
ethene has been reduced as it has gained hydrogen
is the REMOVAL (LOSS) OF OXYGEN
CuO + H2 ——> Cu + H2O
copper(II) oxide has been reduced as it has ‘lost’ oxygen
However as chemistry became more sophisticated, it was realised that another definition was required
...
OXIDATION
REDUCTION
REDOX
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Oxidation and reduction are not only defined as changes in O
and H
OXIDATION & REDUCTION – Better Definitions
...
OXIDATION Removal (loss) of electrons ‘OIL’
species will get less negative or more positive
REDUCTION
REDOX
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Oxidation and reduction are not only defined as changes in O
and H
OXIDATION & REDUCTION – Better Definitions
...
OXIDATION Removal (loss) of electrons ‘OIL’
species will get less negative or more positive
REDUCTION Gain of electrons ‘RIG’species will become more negative or less
positive
REDOX When reduction and oxidation take place
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Oxidation and reduction are not only defined as changes in O
and H
OXIDATION & REDUCTION – Better Definitions
OIL - Oxidation Is the Loss of electrons
RIG - Reduction Is the Gain of electrons
Used to... tell if oxidation or reduction has taken place
work out what has been oxidised and/or reduced
construct half equations and balance redox equations
FOR ATOMS AND SIMPLE IONSThe number of electrons which must be added or removed to become neutral
Atoms Na = 0 neutral already ... no need to add any electrons
Cations Na+ = +1 need to add 1 electron to make Na+ neutral
Anions Cl¯ = -1 need to take 1 electron away to make Cl¯ neutral
OXIDATION NUMBERS (STATES)
Q. What are the oxidation states of the elements in the following?
a) C b) Fe3+ c) Fe2+
d) O2- e) He f) Al3+
Q. What are the oxidation states of the elements in the following?
a) C b) Fe3+ c) Fe2+
d) O2- e) He f) Al3+
Q. What are the oxidation states of the elements in the following?
a) C (0) b) Fe3+ (+3) c) Fe2+ (+2)
d) O2- (-2) e) He (0) f) Al3+ (+3)
Q. What are the oxidation states of the elements in the following?
a) C (0) b) Fe3+ (+3) c) Fe2+ (+2)
d) O2- (-2) e) He (0) f) Al3+ (+3)
OXIDATION STATES
• because CO2 is a neutral molecule, the sum of the oxidation states must be ?
• for this, one element must have a positive OS and the other must be ?
Explanation
MOLECULESThe SUM of the oxidation states adds up to ZERO
ELEMENTS H in H2 = 0 both are the same and must add up to Zero
COMPOUNDS C in CO2 = +4O in CO2 = -2 1 x +4 and 2 x -2 = Zero
HOW DO YOU DETERMINE THE VALUE OF AN ELEMENT’S OXIDATION STATE?• from its position in the periodic table and/or• the other element(s) present in the formula (oxygen is almost always -2 etc)
HOW DO YOU DETERMINE WHICH IS THE POSITIVE ONE?• the more electronegative species will have the negative value
OXIDATION STATES
in SO42- the oxidation state of S = +6 there is ONE S
O = -2 there are FOUR O’s +6 + 4(-2) = -2 so the ion has a 2- charge
COMPLEX IONSThe SUM of the oxidation states adds up to THE CHARGE
e.g. NO3- sum of the oxidation states = - 1
SO42- sum of the oxidation states = - 2
NH4+ sum of the oxidation states = +1
Example SO42-
OXIDATION STATES
What is the oxidation number of Mn in MnO4¯ ?
• the oxidation state of oxygen in most compounds is - 2• there are 4 O’s so the sum of its oxidation states - 8• overall charge on the ion is - 1• therefore the sum of all the oxidation states must add up to - 1• the oxidation states of Mn four O’s must therefore equal - 1• therefore the oxidation state of Mn in MnO4¯is +7
+7 + 4(-2) = - 1
COMPLEX IONSThe SUM of the oxidation states adds up to THE CHARGE
e.g. NO3- sum of the oxidation states = - 1
SO42- sum of the oxidation states = - 2
NH4+ sum of the oxidation states = +1
Example
HYDROGEN +1 except 0 atom (H) and molecule (H2)
-1 hydride ion, H¯ in sodium hydride NaH
OXYGEN -2 except 0 atom (O) and molecule (O2)-1 in hydrogen peroxide, H2O2
+2 in F2O
HALOGENS -1 except 0 atom (X) and molecule (X2)
OXIDATION STATES
CALCULATING OXIDATION STATE - 1
Many elements can exist in more than one oxidation state In compounds, certain elements are used as benchmarks to work out other values
Q. Give the oxidation state of the element other than O, H or F in...SO2 NH3 NO2 NH4
+ IF7 Cl2O7
NO3¯ NO2¯ SO32- S2O3
2- S4O62- MnO4
2-
What is odd about the value of the oxidation state of S in S4O62- ?
Q. Give the oxidation state of the element other than O, H or F in...SO2 NH3 NO2 NH4
+ IF7 Cl2O7
NO3¯ NO2¯ SO32- S2O3
2- S4O62- MnO4
2-
What is odd about the value of the oxidation state of S in S4O62- ?
OXIDATION STATES
A. The oxidation states of the elements other than O, H or F are
SO2 O = -2 2 x -2 = - 4 overall neutral S = +4
NH3 H = +1 3 x +1 = +3 overall neutral N = - 3
NO2 O = -2 2 x -2 = - 4 overall neutral N = +4
NH4+ H = +1 4 x +1 = +4 overall +1 N = - 3
IF7 F = -1 7 x -1 = - 7 overall neutral I = +7
Cl2O7 O = -2 7 x -2 = -14 overall neutral Cl = +7
NO3¯ O = -2 3 x -2 = - 6 overall -1 N = +5
NO2¯ O = -2 2 x -2 = - 4 overall -1 N = +3
SO32- O = -2 3 x -2 = - 6 overall -2 S = +4
S2O32- O = -2 3 x -2 = - 6 overall -2 S = +2
MnO42- O = -2 4 x -2 = - 8 overall -2 Mn = +6
METALS • have positive values in compounds
• value is usually that of the Group Number Al is +3
• where there are several possibilities the values go no higher than the Group No. Sn can be +2 or +4
Mn can be +2,+4,+6,+7
NON-METALS • mostly negative based on their usual ion Cl usually -1 • can have values up to their Group No. Cl +1 +3 +5 or +7
OXIDATION STATES
CALCULATING OXIDATION STATE - 2
The position of an element in the periodic table can act as a guide
OXIDATION STATES
Q. What is the theoretical maximum oxidation state of the following elements?
Na P Ba Pb S Mn Cr
What will be the usual and the maximum oxidation state in compounds of?
Li Br Sr O B N +1
Q. What is the theoretical maximum oxidation state of the following elements?
Na P Ba Pb S Mn Cr
What will be the usual and the maximum oxidation state in compounds of?
Li Br Sr O B N +1
METALS • have positive values in compounds
• value is usually that of the Group Number Al is +3
• where there are several possibilities the values go no higher than the Group No. Sn can be +2 or +4
Mn can be +2,+4,+6,+7
NON-METALS • mostly negative based on their usual ion Cl usually -1 • can have values up to their Group No. Cl +1 +3 +5 or +7
CALCULATING OXIDATION STATE - 2
The position of an element in the periodic table can act as a guide
OXIDATION STATES
CALCULATING OXIDATION STATE - 2
The position of an element in the periodic table can act as a guide
A. What is the theoretical maximum oxidation state of the following elements?
Na P Ba Pb S Mn Cr+1 +5 +2 +4 +6 +7 +6
What will be the usual and the maximum oxidation state in compounds of?
Li Br Sr O B NUSUAL +1 -1 +2 -2 +3 -3 or +5MAXIMUM +1 +7 +2 +6 +3 +5
manganese(IV) oxide shows that Mn is in the +4 oxidation state in MnO2
sulphur(VI) oxide for SO3 S is in the +6 oxidation state
dichromate(VI) for Cr2O72- Cr is in the +6 oxidation state
phosphorus(V) chloride for PCl5 P is in the +5 oxidation state
phosphorus(III) chloride for PCl3 P is in the +3 oxidation state
OXIDATION STATES
THE ROLE OF OXIDATION STATE IN NAMING SPECIES
To avoid ambiguity, the oxidation state is often included in the name of a species
Q. Name the following... PbO2
SnCl2
SbCl3
TiCl4
BrF5
OXIDATION STATES
Q. Name the following... PbO2 lead(IV) oxide
SnCl2 tin(II) chloride
SbCl3 antimony(III) chloride
TiCl4 titanium(IV) chloride
BrF5 bromine(V) fluoride
manganese(IV) oxide shows that Mn is in the +4 oxidation state in MnO2
sulphur(VI) oxide for SO3 S is in the +6 oxidation state
dichromate(VI) for Cr2O72- Cr is in the +6 oxidation state
phosphorus(V) chloride for PCl5 P is in the +5 oxidation state
phosphorus(III) chloride for PCl3 P is in the +3 oxidation state
THE ROLE OF OXIDATION STATE IN NAMING SPECIES
To avoid ambiguity, the oxidation state is often included in the name of a species
REDOX When reduction and oxidation take place
OXIDATION Removal (loss) of electrons ‘OIL’species will get less negative or more positive
REDUCTION Gain of electrons ‘RIG’species will become more negative or less positive
REDOX REACTIONS
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Oxidation and reduction are not only defined as changes in O and H
+7+6+5+4+3+2+1 0-1-2-3-4
REDUCTION
OXIDATION
REDOX When reduction and oxidation take place
OXIDATION Removal (loss) of electrons ‘OIL’species will get less negative or more positive
REDUCTION Gain of electrons ‘RIG’species will become more negative or less positive
REDUCTION in O.N. Species has been REDUCED
e.g. Cl is reduced to Cl¯ (0 to -1)
INCREASE in O.N. Species has been OXIDISED
e.g. Na is oxidised to Na+ (0 to +1)
REDOX REACTIONS
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Oxidation and reduction are not only defined as changes in O and H
+7+6+5+4+3+2+1 0-1-2-3-4
REDUCTION
OXIDATION
REDUCTION in O.S. INCREASE in O.S.Species has been REDUCED Species has been OXIDISED
REDOX REACTIONS
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Q. State if the changes involve oxidation (O) or reduction (R) or neither (N)
Fe2+ —> Fe3+
I2 —> I¯
F2 —> F2O
C2O42- —> CO2
H2O2 —> O2
H2O2 —> H2O
Cr2O72- —> Cr3+
Cr2O72- —> CrO4
2-
SO42- —> SO2
REDOX REACTIONS
REDUCTION in O.S. INCREASE in O.S.Species has been REDUCED Species has been OXIDISED
OXIDATION AND REDUCTION IN TERMS OF ELECTRONS
Q. State if the changes involve oxidation (O) or reduction (R) or neither (N)
Fe2+ —> Fe3+ O +2 to +3 I2 —> I¯ R 0 to -1
F2 —> F2O R 0 to -1
C2O42- —> CO2 O +3 to +4
H2O2 —> O2 O -1 to 0
H2O2 —> H2O R -1 to -2
Cr2O72- —> Cr3+ R +6 to +3
Cr2O72- —> CrO4
2- N +6 to +6
SO42- —> SO2 R +6 to +4
OXIDATION STATES - Review
CALCULATING OXIDATION STATE – MOST IMPORTANT
Q. What is the oxidation state of each element in the following compounds/ions ?
CH4
PCl3
NCl3
CS2
ICl5
BrF3
PCl4+
H3PO4
NH4Cl
H2SO4
MgCO3
SOCl2
OXIDATION STATES
CALCULATING OXIDATION STATE - 2
Q. What is the oxidation state of each element in the following compounds/ions ?
CH4 C = - 4 H = +1
PCl3 P = +3 Cl = -1
NCl3 N = +3 Cl = -1
CS2 C = +4 S = -2
ICl5 I = +5 Cl = -1
BrF3 Br = +3 F = -1
PCl4+ P = +5 Cl = -1
H3PO4 P = +5 H = +1 O = -2
NH4Cl N = -3 H = +1 Cl = -1
H2SO4 S = +6 H = +1 O = -2
MgCO3 Mg = +2 C = +4 O = -2
SOCl2 S = +4 Cl = -1 O = -2