RedOx Reactions 1552
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Transcript of RedOx Reactions 1552
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Balancing Redox Equations:Balancing Redox Equations:
following the electronsfollowing the electrons
Review: Oxidation and reductionReview: Oxidation and reduction
Oxidation numbersOxidation numbers
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Review: Oxidation - reductionReview: Oxidation - reduction
Oxidation is loss of electronsOxidation is loss of electrons
Reduction is gain of electronsReduction is gain of electrons
Oxidation is always accompanied by reductionOxidation is always accompanied by reduction he total number of electrons is !ept constanthe total number of electrons is !ept constant
Oxidi"ing agents oxidi"e and areOxidi"ing agents oxidi"e and are
themselves reducedthemselves reduced Reducing agents reduce and areReducing agents reduce and are
themselves oxidi"edthemselves oxidi"ed
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#uggets of redox processes#uggets of redox processes
$here there is oxidation there is$here there is oxidation there is alwaysalways
reductionreduction
Oxidizing agentOxidizing agent Reducing agentReducing agent
%s%s itselfitselfreducedreduced %s%s itselfitselfoxidi"edoxidi"ed
GainsGainselectronselectrons LosesLoseselectronselectrons
&auses oxidation&auses oxidation &auses reduction&auses reduction
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Oxidation numbers reviewOxidation numbers review
'etals are more (cation-li!e('etals are more (cation-li!e(
)ave positive oxidation)ave positive oxidation
numbersnumbers
#onmetals are (anion-li!e(#onmetals are (anion-li!e( )ave negative oxidation)ave negative oxidation
numbers*numbers*
Oxidation number is the number of electronsOxidation number is the number of electrons
gained or lost by the element in ma!ing agained or lost by the element in ma!ing a
compoundcompound
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+redicting oxidation numbers+redicting oxidation numbers
Oxidation number of atoms in element is "ero in all casesOxidation number of atoms in element is "ero in all cases
Oxidation number of element in monatomic ion is equal toOxidation number of element in monatomic ion is equal tothe chargethe charge
sum of the oxidation numbers in a compound is "erosum of the oxidation numbers in a compound is "ero
sum of oxidation numbers in polyatomic ion is equal to thesum of oxidation numbers in polyatomic ion is equal to thechargecharge
, has oxidation number ., has oxidation number .
) has oxidn no* /.0 except in metal hydrides where it is ) has oxidn no* /.0 except in metal hydrides where it is
.. Oxygen isOxygen is usuallyusuall
y1* Except:1* Except: O is . in hydrogen peroxide2 and other peroxidesO is . in hydrogen peroxide2 and other peroxides
O is .31 in superoxides 4OO is .31 in superoxides 4O11
%n O,%n O,11O is /1O is /1
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+osition of element in periodic table+osition of element in periodic table
determines oxidation numberdetermines oxidation number
5.6 is /.5.6 is /.
516 is /1516 is /1
576 is /7 8some rare exceptions9576 is /7 8some rare exceptions9
56 are 7 in compounds with metals2 ) or with #)56 are 7 in compounds with metals2 ) or with #);/;/
**Exceptions are in compounds to the right0 in which caseExceptions are in compounds to the right0 in which caseuse rules 7 and ;*use rules 7 and ;*
5
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Redox equationsRedox equations
#et ionic equations summari"e the#et ionic equations summari"e the
essentials of a reaction without including allessentials of a reaction without including all
the particles presentthe particles present
Redox equations are a subset which involveRedox equations are a subset which involve
electron transferelectron transfer
$ithout being given all the information2$ithout being given all the information2balancing redox equations involvesbalancing redox equations involves
balancing electron flowbalancing electron flow
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Balancing redox equations:Balancing redox equations:
systematic methodssystematic methods
Oxidation number method trac!ingOxidation number method trac!ing
changes in the oxidation numberschanges in the oxidation numbers
)alf-reaction method trac!ing changes in)alf-reaction method trac!ing changes inthe flow of electronsthe flow of electrons
>ame principles2 different emphasis>ame principles2 different emphasis $e will examine the half-reaction method$e will examine the half-reaction method
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he )alf-Reaction methodhe )alf-Reaction method
6ny redox process can be written as the6ny redox process can be written as the
sum of two half reactions: one for thesum of two half reactions: one for the
oxidation and one for the reductionoxidation and one for the reduction
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>ix habits of the redox equation>ix habits of the redox equation
balancerbalancer
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>E+ .: the unbalanced equation>E+ .: the unbalanced equation
?ichromate ion reacts with chloride ion to?ichromate ion reacts with chloride ion to
produce chlorine and chromium 8%%%9produce chlorine and chromium 8%%%9
)()()()( 232
72 aqClaqCraqClaqOCr ++ +
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>E+ 1: identify the oxidi"ed and>E+ 1: identify the oxidi"ed and
reduced and write the half reactionsreduced and write the half reactions
Oxidation half-reactionOxidation half-reaction
Reduction half-reactionReduction half-reaction
)()( 2 aqClaqCl
)()( 3272 aqCraqOCr +
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>E+ 7: Balance the half reactions>E+ 7: Balance the half reactions
OxidationOxidation
ReductionReduction
)()(2 2 aqClaqCl
)(2)( 32
72 aqCraqOCr +
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'aterial balance with )'aterial balance with )11O and )O and )// or O)or O)--
>trategy: add )>trategy: add )11O to the side that lac!s forO to the side that lac!s for
O and add )O and add )// 8the reaction is in acid8the reaction is in acidsolution9 to the other sidesolution9 to the other side
%n basic solution we add O)%n basic solution we add O) --and )and )11OO
instead of )instead of )11O and )O and )//respectivelyrespectively
est equation for both atoms and chargesest equation for both atoms and charges
)(8)()()(16)(10)( 222
4 522 lOHaqBraqMnaqHaqBraqMnO ++++ ++
)()()(2)( 22
4 5252 aqBraqMnaqBraqMnO ++ +
(16)()()(8)(10)( 22
24 522 aqOHaqBraqMnaqOHaqBraqMnO +
++++
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>E+ ;: 'aterial balance>E+ ;: 'aterial balance
6dd )6dd )11O to the side lac!ing O and add )O to the side lac!ing O and add )//toto
the other side 8for reactions in acid solution9the other side 8for reactions in acid solution9
Oxidation reaction unchangedOxidation reaction unchanged
Reduction reactionReduction reaction
)()(2 2 aqClaqCl
)(7)(2)()(14 232
72 lOHaqCraqOCraqH ++ ++
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>E+ : Balance half-reactions for>E+ : Balance half-reactions for
charge by addition of electronscharge by addition of electrons
BalanceBalance chargeschargeson both sides of eachon both sides of each
half-reactionhalf-reaction
1 x -. @1 x -. @ 11x -.x -.
.; x /. / -1 /.; x /. / -1 /
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>E+ cont: 'ultiply by factors to>E+ cont: 'ultiply by factors to
balance total electronsbalance total electrons
Overall change in electrons must be "eroOverall change in electrons must be "ero
'ultiply the oxidation half reaction by'ultiply the oxidation half reaction by 77
7 x 1 @
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>E+ E+
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Balanced molecular equationBalanced molecular equation
6dd in the spectators: there will always be6dd in the spectators: there will always be
space*space*
Reagents were 4Reagents were 411&r&r11OO==2 #a&l and )2 #a&l and )11>O>O;;
#et ionic equation#et ionic equation
Balanced molecular equationBalanced molecular equation
)(7)(3)(2)(6)()(14 2232
72 lOHaqClaqCraqClaqOCraqH ++++ ++
)(7)()(3)()()(6)()(7242234272242
lOHaqSOKaqClaqSOCraqNaClaqOCrKaqSOH +++++