Redox, Electrochemistry, and Radioactivity

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Redox, Electrochemistry, and Radioactivity

• --Whew.

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Redox

• A reduction is a gain of electrons, an oxidation
  is a loss of electrons
• A reduction is always conjoined with an oxidation
  (electrons are neither created nor destroyed,
  charges must balance)
• Remember OILRIG

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OILRIG

• Oxidation is loss of electrons
• Reduction is gain of electrons

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OrLEO says GER

• Loss of electrons is oxidation
• Gain of electrons is reduction

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For example

• Cu2(aq)Fe(s)?Fe2(aq)Cu(s)
• (right?)

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For example

• Cu2(aq)Fe(s)?Fe2(aq)Cu(s)
• (right?)
• The iron loses custody of its electrons to form
  the 2 ion.
• The iron is oxidized to an iron (II) ion, the
  copper ion is reduced to copper atom

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For example

• 2H2 O2?2H2O
• (right?)

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For example

• 2H2 O2?2H2O
• (right?)
• The hydrogen loses (partial) custody of its
  electrons when it makes the polar covalent bond.

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For example

• 2H2 O2?2H2O
• (right?)
• The hydrogen loses custody of its electrons when
  it makes the polar covalent bond.
• The hydrogen is oxidized, the oxygen is reduced

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In general

• If an atom forms a (-) ion, it has been
  reducedhappens to nonmetals
• If an atom forms a () ion, it has been
  oxidizedhappens to metals
• Combining with O2 (or F2 or Cl2) is an
  oxidationthe O2 (or F2 or Cl2) is reduced

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In general

• If an atom forms a (-) ion, it has been
  reducedhappens to nonmetals
• A (-) ion forming an element is an oxidation
• If an atom forms a () ion, it has been
  oxidizedhappens to metals
• A () ion forming an element is a reduction
• Combining with O2 (or F2 or Cl2) is an
  oxidationthe O2 (or F2 or Cl2) is reduced

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Mark the oxidation and reduction

• 2H2 O2?2H2O

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Mark the oxidation and reduction
reduction

• 2H2 O2?2H2O

oxidation
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Mark the oxidation and reduction
reduction

• 2H2 O2?2H2O

oxidation
Hydrogen is the reducing agent
Oxygen is the oxidizing agent
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Mark the oxidation and reduction
reduction

• 2H2 O2?2H2O

oxidation
Hydrogen is the reducing agent
Oxygen is the oxidizing agent
(it gets reduced)
(it gets oxidized)
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Mark the oxidation and reduction (include the
agents and what happens to each)

• Cu2(aq)Fe(s)?Fe2(aq)Cu(s)

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Which gets oxidized? Which gets reduced?

• 6Li N2 ?2 Li3N
• O2 N2 ? 2 NO
• 16K S8 ? 8 K2S
• S8 16F2 ? 8 SF4
• Br2 2NaI ? I2 2 NaBr
• 2NaCl ? 2 Na Cl2
• H2 Cl2 ? 2 HCl

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Which gets oxidized? Which gets reduced?

• 6Li N2 ?2 Li3N
• O2 N2 ? 2 NO
• 16K S8 ? 8 K2S
• S8 16F2 ? 8 SF4
• Br2 2NaI ? I2 2 NaBr
• 2NaCl ? 2 Na Cl2
• H2 Cl2 ? 2 HCl

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Which gets oxidized? Which gets reduced?

• 6Li N2 ?2 Li3N
• O2 N2 ? 2 NO
• 16K S8 ? 8 K2S
• S8 16F2 ? 8 SF4
• Br2 2NaI ? I2 2 NaBr
• 2NaCl ? 2 Na Cl2
• H2 Cl2 ? 2 HCl

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What if its not so easy?

• 2NH3NaOCl?N2H4NaClH2O

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Oxidation Numbers

• Summary of Oxidation State Rules    
• Free element Oxidation State 0
• Compound total Oxidation State 0
• Ion Oxidation State its charge
• Oxygen Oxidation State -2
• (except peroxides -1 each)
• Hydrogen Oxidation State 1
• (except hydrides -1)

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What is the oxidation number?

• of each atom in sodium hypochlorite
• NaOCl

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What is the oxidation number?

• NaOCl

Sodium hypochlorite is a compound, all together
oxidation numbers 0
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What is the oxidation number?

• 1 .
• NaOCl

The Na ion has 1 charge Oxidation number 1
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What is the oxidation number?

• 1 .
• NaOCl

The OCl- ion has -1 charge Oxidation numbers add
up to -1
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What is the oxidation number?

• 1 -2 .
• NaOCl

The O atom -2 charge Oxidation numbers add up to
-1
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What is the oxidation number?

• 1 -2 1 .
• NaOCl

So the Cl must be 1!
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What is the oxidation number?
NaCl KMnO4 diamond CO2 CO KCN Na4Fe(CN)
6 Fe2O3 Fe3O4 ClO4-
NH3 N2H4 NH4 Au NO3- NO2- NO2 NO
N2O Na2O2
ClO3- ClO2- ClO- Cl- Cl2 P2O5 P4O6
H3PO4 Mg3N2 MgH2
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Now, its easy

• 2NH3NaOCl?N2H4NaClH2O

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Now, its easy

• -3 1 1 -2 1 -2 1
  1 -1 1 -2
• 2NH3NaOCl?N2H4NaClH2O

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Now, its easy
reduction

• -3 1 1 -2 1 -2 1
  1 -1 1 -2
• 2NH3NaOCl?N2H4NaClH2O

oxidation
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Does a redox reaction occur?

• Look for an oxidizing agent and a reducing agent.
  
• If there is one of each, then ask, Can this
  oxidizing agent oxidize this reducing agent
  Answer by comparing reduction potentials. (page
  688)
• (Dont memorize a rule, compare the values to a
  reaction you know will occur)

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Does a redox reaction occur?

• If you combine
• Na and Fe3?
• Cl- and Ag?
• Cu and K ?
• Pb2 and I- ?
• Fe2 and Mg?

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Does a redox reaction occur?

• If you combine
• Na and Fe3?
• Cl- and Ag?
• Cu and K ?
• Pb2 and I- ?
• Fe2 and Mg?

Can be reduced, but not oxidized further
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Does a redox reaction occur?

• If you combine
• Na and Fe3?No. There is no reducer.
• Cl- and Ag?
• Cu and K ?
• Pb2 and I- ?
• Fe2 and Mg?

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Does a redox reaction occur?

• If you combine
• Na and Fe3?No. There is no reducer.
• Cl- and Ag?No. There is no oxidizer.
• Cu and K ?No. This oxidizer cant do it
• Pb2 and I- ?No, but it will precipitate.
• Fe2 and Mg?Yes.
• Fe2 Mg ? Fe and Mg2

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Redoxhalf reactions

• Balance the atoms
• Add H2O and H to balance oxygen and hydrogen
• Rectify the electrons, add and cancel
• Check that charges are balanced
• (Add OH- if the reaction is specified as in a
  basic solution)

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Try it.

• S2O3-2 NO3- ?
• H2O2 Fe2 ?
• Cr2O7-2 I- ?
• MnO4- C2H5OH ?

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Try it.

• S2O3-2 NO3- ? SO4-2 NO
• H2O2 Fe2 ? H2O Fe3
• Cr2O7-2 I- ? Cr3 I2
• MnO4- C2H5OH ? Mn2 CO2 H2O

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Try it.

• 3x(S2O3-2 5H2O? 2 SO4-2 10H 8 e-)
• 8x(NO3- 4H 3 e- ? NO 2 H2O)
• 3S2O3-2 15H2O? 6 SO4-2 30H 24 e-)
• 8NO3- 32H 24 e- ? 8NO 16H2O)
• 3S2O3-28NO3-2H?6SO4-2 8NOH2O

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Reduction potentials

• -- Measured as compared to the reduction of 2H
  2e- ? H2. (0.00V)
• Half reactions that can accomplish this have (-)
  reduction potentials
• Half reactions that force the reverse have ()
  reduction potentials

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Reduction potentials

• Specifically Magnesium reduces H
• 2H Mg ? Mg2 H2 which implies that
• Mg2 2 e- ? Mg
• has a Eolt0
• While bromine oxidizes hydrogen gas
• H2 Br2 ? 2H 2Br - which implies that
• Br2 2 e- ? 2Br
• has a Eogt0

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Electrochemical Cells

• When half reactions are separated, and the
  electrons are connected in a circuit.
• A salt bridge is needed to allow charges to
  migrate to offset the motion of electrons
• Cathodereduction
• An electrode carries electrons to or from a half
  reaction

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Shorthand notation

• The Danielle Cell, using copper and zinc,
• ZnZn2Cu2Cu
• makes 1.1 V

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ZnZn2Cu2Cu

• (or, in general)
• product reactant
• Anode of of cathode
• oxidation reduction

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If non-metals are used

• PtH2H2OO2H2OPt
• The (non-reactive) metal electrode is noted
  outside the bars

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Standard cell potentials

• EoEred-Eox

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Be able to

• Sketch a cell (include salt bridge and circuit)
• Label anode and cathode
• Write the half reactions, complete reaction
• Calculate Eo, show direction of electron flow
• Describe the oxidation and reductionwith mass
  changes, observations.
• Read and write the shorthand notation

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Electrolytic Cells

• Applying an external voltage will allow a
  non-spontaneous reaction to occur.
• 2H2O?2H2O2 is not spontaneous (Right?)
• If you apply a voltage to water (with some
  electrolyte added to carry a charge), it will
  decompose (or electrolyse)

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Nuclear Chemistry

• --breaks the rules that one atom cannot be
  converted to another.
• Chemistry is the dance of the electronsnuclear
  reactions change the nuclei of atoms
• --charge and mass are still conserved.

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Nuclide Notation

• A nuclide is a nucleus or atom of a specific
  isotope of an element

K
39
19

• This is potassium-39. It has 19 protons (atomic
  number 19), making it potassium, and 20
  neutrons, making a mass number of 39

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How many p, n, e- in each?What is the mass
number and atomic number?
Cl-
36
I-
131
H
3
17
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1
Sr2
90
Th
228
Fe3
59
38
90
26
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Natural decays

• athe loss of a particle from a nuclide
• --The a particle is composed of 2p and 2n, the
  4He nucleus
• --decreases the mass by 4 and the atomic number
  by 2
• bemission of an electron (b particle) from the
  nucleus by the conversion of a n ? p e-
• --the electron is the b particle
• --increases the atomic number by 1, does not
  affect mass

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Write the reaction

• Argon-39 undergoes a b decay
• Thorium-228 undergoes an a decay
• An a decay forms lead-204
• A b decay forms nitrogen-14
• A natural decay forms Sc-45 from Ca-45
• A natural decay forms Ac-227 from Pa-231

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Notice what they do

• A b decay lowers the n/p ratio in small nuclei,
  or when the ratio is too large.
• An a decay lowers the total size, and raises the
  n/p in large nuclides, or when the ratio is too
  small.

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What is too large or too small?
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What is too large or too small?
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What is too large or too small?
b decay
a decay
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What is too large or too small?
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What is too large or too small?
np 21
np 11
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This just in.

• Researchers report the first creation of the
  long-lived nucleus hassium-270, a "doubly magic"
  combination of 108 protons and 162 neutrons. Its
  long lifetime of 22 seconds supports the theory
  of an "island of stability" for the heaviest
  elements. (J Dvorak et al. 2006 Phys. Rev. Lett.
  97, 242501)

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Nuclear reactions

• Many nuclear reactions involve colliding nuclei
  or smaller particles at some significant fraction
  of the speed of light,
• --find the missing particle by balancing mass and
  charge.

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Particles might include

• p
• n
• e- (AKA b)
• d
• a
• g (OK, its not a particle, but its often
  written in)

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In comparison

• Physical changes
• joules/mole range
• Chemical changes
• kilojoules/mole range
• Nuclear changes
• megajoules/mole range

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Fission vs Fusion

• Fissionbreaking up large nuclei
• --natural radioactive decay of large atoms
• --used for nuclear power
• Fusioncombining small nuclei
• --occurs naturally in stars
• --prospects for nuclear energyno radioactive
  byproducts
• Both are transmutationsone nuclide is converted
  into another

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Consider the relationships

• Half life
• Original amount
• Final amount
• Time elapsed

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Consider the relationships

• AA0(1/2)
• A is the amount of the sample remaining
• A0 is the original amount in the sample
• t is the time that has passed, and
• t 1/2 is the half-life of the nuclide

t/t1/2
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Please notice

• AA0(1/2)
• A / A0 is the fraction remaining
• t / t 1/2 is the number of half-lifes that have
  passed

t/t1/2
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Try it.

• Hydrogen-3 has a half life of 12.3 years. If you
  start with a 20 g sample of H-3
• --how much is left after 12.3 years?
• --how much is left after 24.6 years?
• --how much is left after 30.2 years?

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Try it.

• Br-82 has a half life of 35.3 hours. If you
  start with a 6.5 mg sample of Br-82
• --how much is left after 4 days?
• --how long will it take to reach .75 mg?

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Try it.

• Br-82 has a half life of 35.3 hours. If you
  start with a 6.5 mg sample of Br-82
• --how much is left after 4 days?
• --how long will it take to reach .75 mg?

How do you solve for an exponent?
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Use a log function

• log (A/A0) log(1/2)
• log (A/A0) log(1/2)
• log (A/A0)
• log(1/2)

t/t1/2
t/t1/2
t/t1/2
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Try it.

• Br-82 has a half life of 35.3 hours. If you
  start with a 6.5 mg sample of Br-82
• --how much is left after 4 days?
• --how long will it take to reach .75 mg?

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Try it.

• If you start with 1.38 mg of U-234 and t1/22.44
  x 105 yrs for its decay
• --how much is left after 20,000 years?
• --how long will it take to reach 0.40 mg?

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Try it.

• A .350 mg sample of K-42 decays to only .066 mg
  in 29.7 hours.
• --what is the half life?
• --how much was left after 20.0 hours?
• --how long will it take to reach .010 mg?

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Th-th-thats all, folks.
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Atomic theory

• All matter is composed of atoms.
• --atoms of one element are identical
• --atoms of different elements are different
• --reactions form different combinations of
  atoms, not different atoms
• Atoms are composed of protons, neutrons, and
  electrons.

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• (Are all of the little kids in bed?Now we can
  tell you the real story)

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Modern Theory
In this Universe, you will find
Bosons (force mediating particles)
Fermions
and
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Modern Theory
Bosons (force mediating particles) include
g, (electromagnetic force) Zo, (weak nuclear
force) Gluons (Strong nuclear force) Graviton
(gravity) W, (weak nuclear force) Higgs
(mediates mass)
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Modern Theory
Fermions are the fundamental particles, including
Quarks
and
Leptons
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Modern Theory
top (formerly known as truth)
up
Types of quarks include
down
charm
bottom (formerly known as beauty)
strange
(and their antiparticles)
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Modern Theory
Leptons include
Electrons, e-, Muons, m, Tauons, t, and three
types of neutrinos ?e, ?m, ?t
(and their antiparticles)
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Modern Theory
Combinations of quarks make hadrons, either
Mesons (2 quarks each) Including p, K-, r,
B0, ?c
Baryons (3 quarks each) including p, n, p-, L,
?-
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Modern Theory
In this Universe, you will find
Bosons (force mediating particles) g,
(electromagnetic force Zo, (weak nuclear
force) Gluons (Str. nuclear force) Graviton
(gravity) W,(weak nuclear force) Higgs
(mediates mass)
fermions which include the fundamental particles
and
Quarks u,d,c,s,t,b (and anti-particles) Quarks
make up the hadrons, either
Leptons e-,m,t,?e, ?m, ?t (and antiparticles)
Mesons (2 quarks each) p,K-,r,B0,?c
baryons (3 quarks each) including p,n,p-,L,?-