rules for assigning oxidation #’s

Rules for Assigning Rules for Assigning Oxidation #’sOxidation #’s

Elements by themselves are neutralElements by themselves are neutral

Ox # = 0Ox # = 0

Ex: NaEx: Na00, O, O2200, Mg, Mg00

Monoatomic Ions show their oxidation # as Monoatomic Ions show their oxidation # as their written chargetheir written charge

Ex: HEx: H+1+1, Cl, Cl-1-1, Al, Al+3+3

Group #1 ElementsGroup #1 Elements in compounds: in compounds:

Ox # = +1Ox # = +1 Ex: LiBr, NaClEx: LiBr, NaCl

Group #2 ElementsGroup #2 Elements in compounds: in compounds:

Ox # = +2Ox # = +2 Ex: MgBrEx: MgBr22, CaCl, CaCl22

AluminumAluminum in compounds: in compounds:

Ox # = +3Ox # = +3 Ex: AlClEx: AlCl33

FluorineFluorine in compounds in compounds

Ox # = -1Ox # = -1 Ex: LiF, MgFEx: LiF, MgF22

HydrogenHydrogen: :

Ox # = +1 (most common)Ox # = +1 (most common)when combined with nonmetalswhen combined with nonmetals

Ex: HCl, HEx: HCl, H22SOSO44, H, H22SS

Ox # = -1Ox # = -1When combined with metals (metal hydrides)When combined with metals (metal hydrides)

Ex: LiH, MgHEx: LiH, MgH22

OxygenOxygen:: Oxidation # = -2 (usually) Oxidation # = -2 (usually)Ex: COEx: CO22, H, H22OO

Special Cases:Special Cases:Peroxides: Oxygen is a diatomic ion (OPeroxides: Oxygen is a diatomic ion (O22))-2-2 with with

total charge of -2, each oxygen has -1 chargetotal charge of -2, each oxygen has -1 chargeEx: HEx: H22OO22, BaO, BaO22

When bonded with Fluorine: Ox # = +2When bonded with Fluorine: Ox # = +2Ex: OFEx: OF22

How to Find Charges If No “Rule”?How to Find Charges If No “Rule”?

Sum of Individual Ox # of all the elements Sum of Individual Ox # of all the elements in a compound = 0in a compound = 0All compounds are NEUTRALAll compounds are NEUTRAL

Ex: NaClOEx: NaClO33

What is the ox # for each element?What is the ox # for each element?

Draw your Lines….Draw your Lines….

How to Find Charges If No “Rule”?How to Find Charges If No “Rule”?

Sum of Ox # of all atoms in a polyatomic Sum of Ox # of all atoms in a polyatomic ion is equal to the charge of that ion.ion is equal to the charge of that ion.

Ex: POEx: PO44-3-3

What is the charge of each element?What is the charge of each element?

Let’s PracticeLet’s Practice

What is the oxidation number of sulfur in What is the oxidation number of sulfur in NaNa22SS22OO33??

(1) -1 (1) -1

(2) +6(2) +6

(3) +2 (3) +2

(4) +4 (4) +4

What is the oxidation number of chromium What is the oxidation number of chromium in the chromate ion, CrOin the chromate ion, CrO4 4

2–2– ? ?

(1) +6 (1) +6

(2) +3(2) +3

(3) +2 (3) +2

(4) +8 (4) +8

In which compound does chlorine have the In which compound does chlorine have the highest oxidation number? highest oxidation number?

(1) NaClO (1) NaClO

(2) NaClO(2) NaClO33



What is the oxidation number assigned to What is the oxidation number assigned to manganese in KMnOmanganese in KMnO44??

(1) +7 (1) +7

(2) +3(2) +3

(3) +2 (3) +2

(4) +4 (4) +4

Mahjong Oxidation # Game:Mahjong Oxidation # Game:http://www2.stetson.edu/mahjongchem/http://www2.stetson.edu/mahjongchem/

Oxidation and Reduction Oxidation and Reduction ReactionsReactions

Oxidation (Read only)Oxidation (Read only)

Original definition:Original definition:When substances combined with oxygenWhen substances combined with oxygen..

Ex:Ex:All combustion (burning) reactionsAll combustion (burning) reactions

CHCH44(g) + 2O(g) + 2O22(g) (g) COCO22(g) + 2H(g) + 2H22O(l)O(l)

All “rusting” reactionsAll “rusting” reactions

4Fe(s) + 3O4Fe(s) + 3O22(g)(g) 2Fe2Fe22OO33(s)(s)

Reduction (Read Only)Reduction (Read Only)

Original Definition:Original Definition:

Reaction where a substance “gave up” oxygen.Reaction where a substance “gave up” oxygen.

Called “reductions” because they producedCalled “reductions” because they produced

products that were “reduced” in mass becauseproducts that were “reduced” in mass because

gas escaped.gas escaped.

Ex:Ex:

2Fe2Fe22OO33(l) + 3C(s)(l) + 3C(s) 4Fe(l) + 3CO 4Fe(l) + 3CO22(g)(g)

Oxidation/Reduction ReactionsOxidation/Reduction Reactions

Oxidation:Oxidation: LOSS of one or more electrons. LOSS of one or more electrons.

Reduction:Reduction: GAIN of one or more electrons GAIN of one or more electrons

Oxidation & reduction always occur together.Oxidation & reduction always occur together.

• Deal with a movement of Deal with a movement of ELECTRONSELECTRONS

between atoms during a reaction.between atoms during a reaction.

• Electrons travel from what is oxidizedElectrons travel from what is oxidized

towards what is reduced.towards what is reduced.

One atom loses e-, One atom loses e-,

the other gains e-the other gains e-

This is called This is called “electron transfer”“electron transfer”

Remember!!Remember!!

Or…RememberOr…Remember

Redox ReactionsRedox Reactions:: ALWAYSALWAYS involve changes in charge involve changes in charge

If charges don’t change it’s NOT a Redox rxn.If charges don’t change it’s NOT a Redox rxn.

Conservation of “Charge”Conservation of “Charge”

Total electrons lost = Total electrons gainedTotal electrons lost = Total electrons gained

Redox Reactions must balance electrons as well as atoms!


Which changes occur when PtWhich changes occur when Pt2+2+ is reduced? is reduced?

(1) Pt(1) Pt2+2+ gains electrons and its oxidation number increases. gains electrons and its oxidation number increases.

(2) Pt(2) Pt2+2+ gains electrons and its oxidation number decreases. gains electrons and its oxidation number decreases.

(3) Pt(3) Pt2+2+ loses electrons and its oxidation number increases. loses electrons and its oxidation number increases.

(4) Pt(4) Pt2+2+ loses electrons and its oxidation number decreases. loses electrons and its oxidation number decreases.

Answer: 1Answer: 1

Given the balanced equation representing a redox Given the balanced equation representing a redox reaction:reaction:

2Al + 3Cu2Al + 3Cu2+2+ →→ 2Al 2Al3+3+ + 3Cu + 3Cu

Which statement is true about this reaction?Which statement is true about this reaction?

(1) Each Al loses 2e- and each Cu(1) Each Al loses 2e- and each Cu2+2+ gains 3e- gains 3e-

(2) Each Al loses 3e- and each Cu(2) Each Al loses 3e- and each Cu2+2+ gains 2e- gains 2e-

(3) Each Al(3) Each Al3+3+ gains 2e- and each Cu loses 3e- gains 2e- and each Cu loses 3e-

(4) Each Al(4) Each Al3+3+ gains 3e- and each Cu loses 2e- gains 3e- and each Cu loses 2e-

Answer: 2Answer: 2

In an oxidation-reduction reaction, reduction In an oxidation-reduction reaction, reduction is defined as theis defined as the

(1) loss of protons (1) loss of protons

(2) loss of electrons(2) loss of electrons

(3) gain of protons (3) gain of protons

(4) gain of electrons (4) gain of electrons

Which change in oxidation number indicates Which change in oxidation number indicates oxidation?oxidation?

(1) –1 to +2(1) –1 to +2 (2) +2 to –3(2) +2 to –3

(3) –1 to –2 (3) –1 to –2 (4) +3 to +2 (4) +3 to +2

When a neutral atom undergoes oxidation, When a neutral atom undergoes oxidation, the atom’s oxidation statethe atom’s oxidation state

(1) decreases as it gains electrons(1) decreases as it gains electrons

(2) decreases as it loses electrons(2) decreases as it loses electrons

(3) increases as it gains electrons(3) increases as it gains electrons

(4) increases as it loses electrons(4) increases as it loses electrons

Oxidizing/Reducing AgentsOxidizing/Reducing Agents

Oxidizing AgentOxidizing Agent::substance reducedsubstance reduced Gains electronsGains electrons

Reducing Agent:Reducing Agent: substance oxidizedsubstance oxidized Loses electronsLoses electrons

The “Agent” is the “opposite”The “Agent” is the “opposite”

Identify What is Changing in Identify What is Changing in ChargeCharge

What is oxidized and reduced?What is oxidized and reduced?

What are the oxidizing and reducing agents?What are the oxidizing and reducing agents?

Ex:Ex:

3Br3Br22 + 2AlI + 2AlI33 2AlBr2AlBr33 + 3I + 3I22

00 +3 -1 +3 -1 +3 -1 0 +3 -1 0

3Br3Br22 + 2AlI + 2AlI33 2AlBr2AlBr33 + 3I + 3I22

BrBr22 is reduced and is the oxidizing agent is reduced and is the oxidizing agent

II-1-1 is oxidized and is the reducing agent is oxidized and is the reducing agent

What is oxidized and reduced?What is oxidized and reduced?What are the oxidizing and reducing agents?What are the oxidizing and reducing agents?

Mg + CuSOMg + CuSO44 MgSOMgSO44 + Cu + Cu

2K + Br2K + Br22 2KBr2KBr

Cu + 2AgNOCu + 2AgNO33 Cu(NO Cu(NO33))22 + 2Ag + 2Ag

NOTE: NOTE: Atoms in a polyatomic ion DO NOT change in charge!Atoms in a polyatomic ion DO NOT change in charge!

0 +2 +2 00 +2 +2 0

Mg + CuSOMg + CuSO44 MgSOMgSO44 + Cu + CuMg oxidized (reducing agent)Mg oxidized (reducing agent)CuCu+2+2 reduced (oxidizing agent) reduced (oxidizing agent)

0 0 +1 -10 0 +1 -1

2K + Br2K + Br22 2KBr2KBrK oxidized (reducing agent)K oxidized (reducing agent)

BrBr2 2 reduced (oxidizing agent)reduced (oxidizing agent)

00 +1 +1 +2 0+2 0

Cu + 2AgNOCu + 2AgNO33 Cu(NO Cu(NO33))22 + 2Ag + 2AgCu oxidized (reducing agent)Cu oxidized (reducing agent)AgAg+1+1 reduced (oxidizing agent) reduced (oxidizing agent)

Redox or Not Redox Redox or Not Redox (that is the question…)(that is the question…)

Redox Reactions:Redox Reactions: must have atoms changing in must have atoms changing incharge.charge.

Not all reactions are redox.Not all reactions are redox.

Easy way to spot a redox reaction!!!Easy way to spot a redox reaction!!!Look for elements entering and leavingLook for elements entering and leavingcompoundscompounds..

Is it Redox?Is it Redox?

Look for Changes in Charge! Look for Changes in Charge! Are elements entering and leaving compounds?Are elements entering and leaving compounds?

Synthesis:Synthesis:

Ex:Ex: 2H2H22 + O + O22 2H2H22OO

Decomposition:Decomposition:

Ex:Ex: 2KClO2KClO33 2KCl + 3O2KCl + 3O22


SynthesisSynthesis: : YESYES

00 0 0 +1 -2 +1 -2

Ex:Ex: 2H2H22 + O + O22 2H2H22OO

DecompositionDecomposition: : YESYES

+1 +5 -2+1 +5 -2 +1 -1 0 +1 -1 0

Ex:Ex: 2KClO2KClO33 2KCl + 3O2KCl + 3O22


Combustion:Combustion:

CHCH44 + 2O + 2O22 COCO22 + 2H + 2H2200

Single Replacement:Single Replacement:

Zn + CuClZn + CuCl22 ZnClZnCl22 + Cu + Cu


Combustion:Combustion: YESYES-4 +1 0 +4 -2 +1 -2-4 +1 0 +4 -2 +1 -2

CHCH44 + 2O + 2O22 COCO22 + 2H + 2H2200

Single Replacement:Single Replacement:YESYES 0 +2 -1 +2 -1 00 +2 -1 +2 -1 0



Double Replacement:Double Replacement:

AgNOAgNO33 + LiCl + LiCl AgCl + LiNO AgCl + LiNO33


Double Replacement:Double Replacement: NO!!!!NO!!!!

Ions switch partners, but don’t change in chargeIons switch partners, but don’t change in charge

+1 +5 -2 +1 -1 +1 -1 +1 +5 -2+1 +5 -2 +1 -1 +1 -1 +1 +5 -2

AgNOAgNO33 + LiCl + LiCl AgCl + LiNO AgCl + LiNO33

Remember charges of atoms inside polyatomicRemember charges of atoms inside polyatomic

Ions do not change!Ions do not change!


Which equation represents an oxidationWhich equation represents an oxidationreduction reaction?reduction reaction?

(1) CH(1) CH44 + 2O + 2O22 →→ CO CO22 + 2H + 2H22OO

(2) H(2) H22SOSO44 + Ca(OH) + Ca(OH)22 →→ CaSO CaSO44 + 2H + 2H22OO

(3) MgCrO(3) MgCrO44 + BaCl + BaCl22 →→ MgCl MgCl22 + BaCrO + BaCrO44

(4) Zn(NO(4) Zn(NO33))22 + Na + Na22COCO33 →→ 2NaNO 2NaNO33 + ZnCO + ZnCO33

Which reaction is an example of anWhich reaction is an example of anoxidation reduction reaction?oxidation reduction reaction?

(1) AgNO(1) AgNO33 + KI + KI →→AgI + KNOAgI + KNO33

(2) Cu + 2 AgNO(2) Cu + 2 AgNO33 →→ Cu(NO Cu(NO33))22 + 2 Ag + 2 Ag

(3) 2 KOH + H(3) 2 KOH + H22SOSO44 →→ K K22SOSO44 + 2H + 2H22OO

(4) Ba(OH)(4) Ba(OH)22 + 2HCl + 2HCl →→ BaCl BaCl22 + 2H + 2H22OO

Writing Half ReactionsWriting Half Reactions

Redox Reactions are composed of two partsRedox Reactions are composed of two parts

or half reactions.or half reactions.

Half Reactions Show:Half Reactions Show:

Element being oxidized or reduced.Element being oxidized or reduced.

Change in chargeChange in charge

# of moles of e# of moles of e-- being lost or gained being lost or gained

http://www.kentchemistry.com/links/Redox/flash/RedoxOxNumbers.swf

Writing Half ReactionsWriting Half Reactions

0 00 0 +1 -1 +1 -1

2Na + F2Na + F22 2NaF2NaF

Oxidation:Oxidation: NaNa Na Na+1+1 + 1e- + 1e-oror 2Na2Na 2Na 2Na+1 +1 + 2e- + 2e-

Note: e- are “lost” (on the right of arrow)Note: e- are “lost” (on the right of arrow)

Reduction:Reduction: F + 1e-F + 1e- F F-1-1

oror FF22 + 2e- + 2e- 2F 2F-1-1

Note: e- are “gained” (on the left of arrow)Note: e- are “gained” (on the left of arrow)

Ox’s Have Tails!!Ox’s Have Tails!!

Oxidation Half reactions always have Oxidation Half reactions always have “tails” of electrons“tails” of electrons

NaNa Na Na+1+1 + 1e- + 1e-

00 +2 -1 +2 -1 +2 -1 0+2 -1 0


Ox:Ox: ZnZn ZnZn+2+2 + 2e- + 2e-

Red:Red: CuCu+2+2 + 2e- + 2e- CuCu

https://www.youtube.com/watch?v=-wvnX1f7yRYTutorial on Writing Half Reactions

Balancing Simple Redox RxnsBalancing Simple Redox Rxns

Must be:Must be:

Balanced for MassBalanced for Mass

ATOMS balanceATOMS balance

Balanced for ChargeBalanced for Charge

Total e- Lost = Total e- GainedTotal e- Lost = Total e- Gained

Applications of Redox ReactionsApplications of Redox Reactions

Corrosion of MetalsCorrosion of Metals

Metals gets oxidized byMetals gets oxidized by

oxygen in the air formingoxygen in the air forming

metal oxides (rust)metal oxides (rust)

4Fe(s) + 3O4Fe(s) + 3O22(g) (g) →→ 2Fe 2Fe22OO33(s)(s)

Prevention:Prevention: Use paint, oil, Use paint, oil,

““Plating” or attach to negativePlating” or attach to negative

terminal of a battery.terminal of a battery. Gold doesn’t rust…Why?

Ships or pipes made of Fe will “rust Ships or pipes made of Fe will “rust away” into Feaway” into Fe+2 +2 ions when oxidized.ions when oxidized.

Blocks of more reactive metals (see Blocks of more reactive metals (see Table J) like Mg or Zn are attached to Table J) like Mg or Zn are attached to ships or underground pipes.ships or underground pipes.

Electrons travel from more reactive Electrons travel from more reactive metal to less reactive iron preventing it metal to less reactive iron preventing it from oxidizing.from oxidizing.

Aluminum forms an oxide coating that Aluminum forms an oxide coating that protects the metal from further corrosion.protects the metal from further corrosion.

Photograph DevelopmentPhotograph Development involves oxidation and involves oxidation and

reduction of silver atoms and ionsreduction of silver atoms and ions

BleachBleach acts on acts on

stains by oxidizingstains by oxidizing

them, getting reduced them, getting reduced

in the processin the process

ExplosivesExplosives form gases like form gases like

NN22 from nitrogen compounds! from nitrogen compounds!

Car BatteriesCar BatteriesLead/Acid BatteryLead/Acid BatteryLead is both oxidized and reducedLead is both oxidized and reduced

Pb(s) + PbOPb(s) + PbO22(s) + 2H(s) + 2H22SOSO44(aq) → 2PbSO(aq) → 2PbSO44(s) + (s) +

2H2H22O(l)O(l)

http://www.youtube.com/watch?v=jW_KkEhCy68&safe=active

Reactivity of MetalsReactivity of Metals

Reference Table JReference Table J

Metals Higher on Table J Metals Higher on Table J

are more ‘active” are more ‘active”

““Active” metals are Active” metals are

easily oxidized (easily oxidized (loselose electrons), electrons),

and good “reducing agents”and good “reducing agents”

Copper replaces silver!

Single Replacement Reactions:Single Replacement Reactions:Elements higher on Table J “replace” elements that are lower.Elements higher on Table J “replace” elements that are lower.

Cu0(s) + AgNO3(aq) Ag0(s) + CuNO3(aq)

Ag0(s) + CuNO3(aq) wouldn’t happen!!!

Reactivity of NonmetalsReactivity of Nonmetals

Reference Table JReference Table JNonmetals higher on Table J Nonmetals higher on Table J are more “active” are more “active”

““Active” nonmetals Active” nonmetals are more easily reducedare more easily reduced((gaingain electrons), and electrons), and good “oxidizing agents”good “oxidizing agents”

Balancing Harder Balancing Harder Redox ReactionsRedox Reactions

(Honors)(Honors)

Oxidation Number MethodOxidation Number Method(Balancing in Acid Solution)(Balancing in Acid Solution)

• Find ox #’s and use brackets to connect elementsFind ox #’s and use brackets to connect elements

changing in charge.changing in charge.• Balance atoms changing in chargeBalance atoms changing in charge• Find total e- involved in each changeFind total e- involved in each change• If necessary balance e- by multiplicationIf necessary balance e- by multiplication• Balance all other atoms except H and OBalance all other atoms except H and O• Balance oxygen by adding HBalance oxygen by adding H22O to side deficientO to side deficient

• Balance hydrogen by adding HBalance hydrogen by adding H+1+1 to side deficient to side deficient• Check for balance with respect to atoms and charge.Check for balance with respect to atoms and charge.

Half Reaction Method Half Reaction Method (Ion/Electron Method)(Ion/Electron Method)

(In acid solution)(In acid solution)

Separate equation into two “basic” half reactionsSeparate equation into two “basic” half reactions Balance all atoms except H and OBalance all atoms except H and O Balance oxygen by adding HBalance oxygen by adding H22OO Balance hydrogen by adding HBalance hydrogen by adding H+1+1

Balance charge by adding electrons to more Balance charge by adding electrons to more positive sidepositive side

If necessary balance e- by multiplicationIf necessary balance e- by multiplication Add together half reactions and simplifyAdd together half reactions and simplify Check for balance of atoms and chargeCheck for balance of atoms and charge

Crash Course Chemistry: RedoxCrash Course Chemistry: Redoxhttps://www.youtube.com/watch?v=lQ6FBhttps://www.youtube.com/watch?v=lQ6FB

A1HM3s&index=11&list=PL8dPuuaLjXtPHA1HM3s&index=11&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGrzzYuWy6fYEaX9mQQ8oGr

rules for assigning oxidation #’s

Documents

pt2 gains electrons

oxidation number increases

oxidation number decreases

oxidation number of

oxidation number of

highest oxidation number

mahjong oxidation

e answer