Oxidation States and Redox: Oxidation and Reduction

CT04D01Science 10Chemistry

H       He

Li Be   B C N O F Ne

Na

Mg   Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu

Zn Ga Ge A

sSe Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh P

dAg

Cd In Sn S

b Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au

Hg Tl Pb Bi P

o At Rn

Fr Ra Ac Rf Db Sg Bh Hs Mt D

s                

Ce Pr Nd P

mSm Eu Gd T

bDy

Ho Er T

mYb Lu

Th

Pa U Np Pu A

mCm

Bk Cf Es F

m Md No Lr

MetaloidsAlkaline Earths

Alkali Metals

Transition Metals

Non-metals

Weak/Poor Metals

Halogens

Noble Gases

Actinides

Lanthanides

H He

Li Be B C N O F Ne

Na

Mg Al Si P S Cl Ar

K Ca Se Ti V Cr Mn Fe Co Ni C

u Zn Ga Ge As Se

Br Kr

Rb Sr Y Zr N

b Mo Tc Ru Rh Pd

Ag

Cd In Sn S

b Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au

Hg Tl Pb Bi P

oAt

Rn

Fr Ra Ac Rf Db Sg Bh Hs Mt D

s                

Ce Pr Nd

Pm

Sm Eu Gd T

bDy

Ho Er T

mYb Lu

Th Pa U Np Pu A

mCm

Bk Cf Es F

mMd

No Lr

Alkali Metals – lose 1 e

Alkaline Earths – Lose 2 e

IIIA – Lose 3 e

IVA (carbon) – Lose 4 e / Gain 4 e

VA (Nitrogen) – Gain 3 e

VIA (oxygen) – Gain 2 e

Halogen – Gain 1 e

Noble Gases - neutral

Ionic Charges

All elements want to become like the noble gases!

Oxidation NumbersOxidation numbers always refer to single atoms

The oxidation number of an uncombined element is always 0 (this includes diatomics)

(BrINClHOF) Br2, O2, H2, Ne, Zn, Mg, Ca, etc

The oxidation number of Hydrogen is usually +1

HCl, H2SO4

The oxidation number of Oxygen is usually -2

H2O, NO2, et

Oxidation numbers of monatomic ions follow the charge of the ion

O2-, Zn2+

The sum of oxidation numbers is zero for a neutral compound

LiMnO4

The sum of the oxdiation numbers is the charge of the polyatomic ion

SO42-, NO3

-, PO33-

Only when in completely ionic binary compounds will Alkali Metals (+1), Alkaline Earths (+2), Halogens (-1)

NaCl, MgBr2, KF, etc

Polyatomic Ions

+1 -1 -2 -3

Ammonium NH4

+

Chlorate ClO3

-

Sulfate SO4

2-

Phosphate PO4

3-

Chlorite ClO2

-

Sulfite SO3

2-

Phosphite PO4

3-

Nitrate NO3

-

Carbonate CO3

2-

Nitrite NO2

-

Hydroxide OH-

The polyatomic ions will be given to you but you should be very familiar with them by now!! Let’s determine oxidation numbers for each….

Practice Assigning Oxidation Numbers

NO2

N2O5

HClO3

HNO3

Ca(NO3)2

K2CO3

Practice Assigning Oxidation Numbers

NO2N= +4, O = -2

N2O5 N = +5, O = -2

HClO3 H=+1, Cl=+5, O = -2

HNO3 H=+1, N = +5, O = -2

Ca(NO3)2 Ca=+2, N =+5, O= -2

K2CO3K=+1, C=+4, O= -2

Hint: If it includes a polyatomic ion, you know the overall charge, and oxygen will always be -2, find the other oxidation states next

Practice Assigning Oxidation Numbers

Fe(OH)3

K3PO3

CO32-

(NH4)Cl

Fe(ClO2)2

Practice Assigning Oxidation Numbers

Fe(OH)3 Fe =+3, O=-2, H=+1

K3PO3 K=+1, P=+3, O=-2

CO32-

C=+4, O =-2

(NH4)Cl N=3-, H=1+, Cl=-1

Fe(ClO2)2Fe=+2, Cl=3+, O=-2

Redox Equations

NOTE: If you get there! Brakke students will need to

identify which element is oxidized and which is reduced

for a 7

Oxidation-Reduction Reactions

All redox reactions have at least one element oxidized and at least one element reducedOccasionally the same element may undergo both oxidation and reduction. This is known as an auto-oxidation

reduction We will NOT see this until IB

CHEM

Pneumonic Devices….

There are two phrases to help you remember the general practice of oxidation and reduction exchanges LEO says GER OIL RIG

LEO says…..

LEO: Loss of Electrons = OxidationGER: Gain of Electrons = Reduction

GER!

OIL: Oxidation is Loss….RIG: Reduction is Gain….

….of electrons

Oxidation NumbersOxidation is the loss of electrons; Reduction is the gain of electronsOxidation and reduction go together. Whenever a substance loses electrons another substance gains electronsOxidation Numbers are a system that we can use to keep track of electron transfers with a reaction

Using Oxidation NumbersCareful examination of the oxidation numbers of atoms in an equation allows us to determine what is oxidized and what is reduced in an oxidation-reduction reaction

Using Oxidation Numbers

An increase in the oxidation number indicates that an atom has lost electrons and therefore oxidized.A decrease in the oxidation number indicates that an atom has gained electrons and therefore reducedExample 0 +2 +6 -2 +2 +6 -2 0

Zn + CuSO4 ZnSO4 + Cu

Zn: 0 + 2 Oxidized Cu: +2 0 Reduced

ExerciseFor each of the following reactions find the element oxidized and the element reduced

Cl2 + KBr KCl + Br2  Cu + HNO3 Cu(NO3)2

+ NO2 + H2O

HNO3 + I2 HIO3 + NO2

Look on the following slides for answers……

Exercise 1

For each of the following reactions find the element oxidized and the element reduced

0 +1 -1 +1 -1 0

Cl2 + KBr KCl + Br2

Br increases from –1 to 0 OxidizedCl decreases from 0 to –1 ReducedK remains unchanged at +1

Exercise 2

For each of the following reactions find the element oxidized and the element reduced

0 +1 +5 -2 +2 +5 -2 +4 –2 +1 -2

Cu + HNO3 Cu(NO3)2 + NO2 +

H2O

Cu increases from 0 to +2 OxidizedSome N in nitric acid from +5 to +4

ReducedThe nitrogen that ends up in copper nitrate

remains unchanged, same for hydrogen and oxygen

Exercise 3

For each of the following reactions find the element oxidized and the element reduced 1 +5 -2 0 +1 +5 -2 +4 -2

HNO3 + I2 HIO3 + NO2

N is reduced from +5 to +4 ReducedI is increased from 0 to +5 OxidizedThe hydrogen and oxygen remain unchanged.