oxidation-reduction
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Oxidation-Reduction. Dr. Ron Rusay. Balancing Oxidation-Reduction Reactions. Oxidation-Reduction. Oxidation is the loss of electrons. Reduction is the gain of electrons. The reactions occur together. One does not occur without the other. - PowerPoint PPT PresentationTRANSCRIPT
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Oxidation-ReductionOxidation-Reduction
Dr. Ron RusayDr. Ron Rusay
Balancing Oxidation-Reduction Reactions
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Oxidation-ReductionOxidation-Reduction
�OxidationOxidation is the loss of electrons. is the loss of electrons.�ReductionReduction is the gain of electrons. is the gain of electrons.�The reactions occur together. One does The reactions occur together. One does
not occur without the other.not occur without the other.�The terms are used relative to the The terms are used relative to the
change in the change in the oxidation stateoxidation state or or oxidation numberoxidation number of the reactant(s). of the reactant(s).
Oxidation Reduction ReactionsOxidation Reduction Reactions
QUESTIONQUESTION
What is the oxidation number of chromium in ammonium dichromate?
A) +3 B) +4 C) +5 D) +6
QUESTIONQUESTION
Zinc
Select all redox reactions by looking for a change in oxidation number as reactants are converted to products.
I) Ca + 2 H2O → Ca(OH)2 + H2
II) CaO + H2O → Ca(OH)2
III) Ca(OH)2 + H3PO4 → Ca3(PO4)2 + H2O
IV) Cl2 + 2 KBr → Br2 + 2 KCl
A) I and II B) II and III C) I and IV D) III and IV
QUESTIONQUESTION
QUESTIONQUESTION
Cu 2+ Cu (s)
H2 (g) 2 H +
0
0
+2 e-
- 2 e-
Use oxidation numbers to determine what is oxidized and what is reduced.
Number of electrons gained must equal the number of electrons lost.
- 2 e-
+2 e-
Refer to BalancingOxidation-Reduction Reactions
QUESTIONQUESTION
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equationsin acidic solutionsin acidic solutions
1) Determine the oxidation numbers of atoms in both 1) Determine the oxidation numbers of atoms in both reactants and products.reactants and products.
2) Identify and select out those which change 2) Identify and select out those which change oxidation number (“redox” atoms) into separate oxidation number (“redox” atoms) into separate “half reactions”.“half reactions”.
3) Balance the “redox” atoms and charges (electron 3) Balance the “redox” atoms and charges (electron gain and loss must equal!).gain and loss must equal!).
4) In acidic reactions balance oxygen with water 4) In acidic reactions balance oxygen with water then hydrogen from water with acid proton(s).then hydrogen from water with acid proton(s).
1
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equations
FeFe+2+2(aq)(aq)+ Cr+ Cr22OO77
2-2-(aq) (aq) +H+H++
(aq)(aq)---->---->
FeFe3+3+(aq)(aq) + Cr + Cr3+3+
(aq) (aq) + H+ H22OO(l) (l)
??
Fe Fe 2+2+(aq)(aq)+ Cr+ Cr22OO77
2-2-(aq) (aq) +H+H++
(aq)(aq)---->---->
Fe Fe 3+3+(aq)(aq) + Cr + Cr 3+3+
(aq) (aq) + H+ H22OO(l)(l)
1
x x == ?? Cr Cr ; ; 2x+7(-2) 2x+7(-2) = = -2-2; ; x x = = +6+6
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equations
Fe Fe 2+2+(aq)(aq) ---> Fe ---> Fe 3+3+
(aq)(aq)
CrCr22OO772-2-
(aq) (aq) + --> Cr + --> Cr 3+3+(aq) (aq)
CrCr = (= (6+6+))
1
66 (Fe (Fe 2+2+(aq)(aq) -e -e - - ---> Fe---> Fe3+3+
(aq)(aq)))
66 Fe Fe 2+2+(aq)(aq) ---> ---> 6 6 FeFe3+3+
(aq) (aq) + + 6 6 ee - -
CrCr22OO772-2-
(aq) (aq) + 6 e+ 6 e - - --> --> 2 2 CrCr3+3+(aq)(aq)
6 e6 e - -
-e-e - -
22
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equations
66 Fe Fe2+2+(aq)(aq) ---> ---> 6 6 FeFe3+3+
(aq) (aq) + + 6 6 ee - -
CrCr22OO772-2-
(aq) (aq) + 6 e+ 6 e - - --> --> 2 2 CrCr3+3+(aq)(aq)
66 Fe Fe2+2+(aq)(aq)+ Cr+ Cr22OO77
2-2-(aq) (aq) + + ? ? 2nd 2nd HH++
(aq)(aq) ----> ---->
6 6 FeFe3+3+(aq) (aq) + + 2 2 CrCr3+3+
(aq)(aq)+ + ? ? 1st Oxygen 1st Oxygen HH22OO(l) (l)
1
OxygenOxygen == 7 7 2nd (Hydrogen)2nd (Hydrogen) == 1414
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equations
Completely Balanced Equation:Completely Balanced Equation:
66 Fe Fe2+2+(aq)(aq)+ Cr+ Cr22OO77
2-2-(aq) (aq) + + 14 14 HH++
(aq)(aq) ----> ---->
6 6 FeFe3+3+(aq) (aq) + + 2 2 CrCr3+3+
(aq)(aq)+ + 77 HH22OO(l) (l)
1
Dichromate ion in acidic medium converts ethanol, C2H5OH, to CO2 according to the unbalanced equation:
Cr2O72−(aq) + C2H5OH(aq) → Cr3+(aq) + CO2(g) +
H2O(l)
The coefficient for H+ in the balanced equation using smallest integer coefficients is:
A) 8 B) 10 C) 13 D) 16
QUESTIONQUESTION
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Balancing Redox EquationsBalancing Redox Equationsin basic solutionsin basic solutions
1) Determine oxidation numbers of atoms in 1) Determine oxidation numbers of atoms in Reactants and ProductsReactants and Products
2) Identify and select out those which change 2) Identify and select out those which change oxidation number into separate “half reactions”oxidation number into separate “half reactions”
3) Balance redox atoms and charges (electron gain 3) Balance redox atoms and charges (electron gain and loss must equal!)and loss must equal!)
4) In basic reactions balance the Oxygen with 4) In basic reactions balance the Oxygen with hydroxide then Hydrogen from hydroxide with hydroxide then Hydrogen from hydroxide with waterwater
1
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
MnOMnO2 (aq)2 (aq)+ ClO+ ClO331-1-
(aq) (aq) + OH + OH 1-1-aq) aq) ->->
MnOMnO441-1-
(aq) (aq)+ Cl + Cl 1-1-(aq) (aq) + H+ H22OO(l) (l)
MnMn4+4+ (MnO (MnO22) ---> Mn) ---> Mn7+7+ (MnO (MnO4 4 )) 1-1-
ClCl+5+5 (ClO(ClO3 3 )) 1-1-+ + 6 6 ee-- ---> Cl ---> Cl 1-1-
Balancing Redox EquationsBalancing Redox Equationsin basic solutionsin basic solutions
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Electronically Balanced Equation:Electronically Balanced Equation:
22 MnO MnO2 (aq)2 (aq)+ ClO+ ClO331-1-
(aq) (aq) + + 66 e e - - ---->---->
2 2 MnOMnO4 4 1-1- + + Cl Cl 1- 1- + + 6 6 ee--
Balancing Redox EquationsBalancing Redox Equationsin basic solutionsin basic solutions
© Copyright 2002-2010 R.J. Rusay© Copyright 2002-2010 R.J. Rusay
Completely Balanced Equation:Completely Balanced Equation:
22 MnO MnO2 (aq)2 (aq)+ ClO+ ClO331-1-
(aq) (aq) + + 22 OH OH 1- 1- (aq)(aq)---->---->
2 2 MnOMnO4 (aq)4 (aq)1-1- + + Cl Cl 1- 1-
(aq)(aq)+ + 1 1 HH22O O (l)(l)
99 O in productO in product
Balancing Redox EquationsBalancing Redox Equationsin basic solutionsin basic solutions
QUESTIONQUESTIONOxalate ion can be found in rhubarb and spinach (among other green leafy plants). The following unbalanced equation carried out in a basic solution, shows how MnO4
– could be used to analyze samples for oxalate.
MnO4– + C2O4
2– MnO2 + CO32– (basic solution)
When properly balanced, how many OH– are present?
•1•2•3•4