chemistry topic 9 › ourpages › auto › 2016 › 9 › 15... · 2017-05-31 · •chemistry –...

Chemistry Topic 9

Oxidation - Reduction

• Chemistry – Mr. Sinto

• Redox

• Obj: SWBAT define oxidation and reduction and assign oxidation numbers

• Do Now: How do you think electricity is produced?

• NO LATE WORK ACCEPTED THIS SEMESTER!!!

• Oxidation = the LOSS OF ELECTRONS, and increase in oxidation number

• Reduction = the GAIN OF ELECTRONS, and decrease in oxidation number

• Redox = Reduction and Oxidation they MUST occur together

• LEO the lion says GER

• LEO = Lose Electrons Oxidize

• GER = Gain Electrons Reduce

If your oxidation number became more

Positive it got

Oxidized, and if it was

Reduced it became more

Negative

Rules for assigning Oxidation Numbers (Must Memorize: On EVERY REGENTS)

1. The oxidation number of any uncombined element is 0.

Na

Li

Ca

F2

2. The oxidation number of a monatomic ion equals the charge on the ion.

Na+

Cl-

Ca2+

O2-

3. The oxidation number of fluorine in a compound is always -1.

NaF

CaF2

LiF

2 4. Oxygen has an oxidation number of -2 unless it is combined with F (when it is +2), or it is in a peroxide (such as H2O2 or Na2O2), when it is -1.

H2O

Li2O

H2O2

OF2

5. The oxidation state of hydrogen in most of its compounds is +1 unless it is combined with a metal, in which case it is -1.

HCl

H2O

LiH

HF

6. In compounds, the elements of groups 1 and 2 as well as aluminum have oxidation numbers of +1, +2, and +3 respectively.

NaCl

CaO

AlCl3

7. The sum of the oxidation numbers of all atoms in a neutrals compound is 0.

NaCl

HF

HNO3

Li2O

8. The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge of the ion.

Cr2O72-

SO42-

NH4+

Assigning Oxidation Number


• Redox

• Obj: SWBAT properly balance redox reactions.

• Do Now: What are the oxidation numbers of the atoms in CO2

• Homework: Finish worksheet

• 1. N in N2O3

• 2. S in H2SO4

• 3. C

• 4. C in CO

• 5. Na in NaCl

• 6. H in H2O

• 7. Ba in BaCl2

• 8. N in NO2-

• 9. S in Al2S3

• 10. S in HSO4-

• 11. Cl in Fe(ClO2)3

• 12. Fe in Fe(ClO2)3

• 13. N in NO3-

• 14. Cu2+

Redox Reactions

• To determine whether a reaction is a redox, assign oxidation to each atom and see if the number changed.

• If it’s a single replacement it’s redox

Zn + HCl ZnCl2 +H2

NaCl + AgNO3 AgCl + NaNO3

MnO2 + 4 HCl MnCl2 + Cl2 + 2H2O

Which one(s) is/are redox?

• Oxidizing Agent = the species that is REDUCED.

– Helps something else get oxidized

• Reducing Agent = the species that is OXIDIZED

– Helps something else get reduced

Zn + HCl ZnCl2 +H2

MnO2 + 4 HCl MnCl2 + Cl2 + 2H2O

• If they ask what is oxidized or reduced or for the oxidizing or reducing agent answer is always on the left side of the equation


• Redox

• Obj: SWBAT properly balance redox reactions and explain how they are used in everyday life.

• Do Now: What are the oxidation numbers of the atoms in HSO4

-, NO2-

Half Reactions

• Half-reaction = shows EITHER the oxidation or reduction portion of a redox reaction

• Reduction Half-Reaction (electrons on LEFT)

Fe3+(aq) + 3e- Fe(s)

• Oxidation Half-Reaction (electrons on RIGHT)

Fe(s) Fe3+(aq) + 3e-

• To balance a redox equation

– Write the oxidation and reduction half-reactions

– Multiple the equation(s) until electrons are equal

– Add equations together (electrons cancel out)

• Redox reactions must be balanced by

BOTH MASS AND CHARGE

Cu + AgNO3 Cu(NO3)2 + Ag

Oxidation: Cu Cu2+ + 2e-

Reduction: Ag+ + e- Ag

2Ag+ + 2e- 2Ag

Overall: Cu + 2AgNO3 Cu(NO3)2 + 2Ag

Fe + Cu2+ Fe2+ + Cu

Oxidation: Fe Fe2+ + 2e-

Reduction: Cu2+ + 2e- Cu

Already balanced by both mass and charge

Fe3+ + Sn2+ Fe2+ + Sn4+

Oxidation: Sn2+ Sn4+ + 2e-

Reduction: Fe3+ + 1e- Fe2+

Multiply the reduction by 2

2Fe3+ + 2e- 2Fe2+

Add equations together (cancel out electrons)

Sn2+ + 2Fe3+ Sn4+ + 2Fe2+

Fe3+ + Ni Fe2+ + Ni2+

Oxidation: Ni Ni2+ + 2e-

Reduction: Fe3+ + 1e- Fe2+


2Fe3+ + 2e- 2Fe2+


Ni + 2Fe3+ Ni2+ + 2Fe2+

Cu(s) + Ag+(aq) → Cu2+

(aq) + Ag(s)


Reduction: Ag+ + 1e- Ag


2Ag+ + 2e- 2Ag


Cu + 2Ag+ Cu2+ + 2Ag

Cu + Fe3+ Cu2+ + Fe


Reduction: Fe3+ + 3e- Fe

Multiply the oxidation by 3 and reduction by 2

3Cu 3Cu2+ + 6e-

2Fe3+ + 6e- 2Fe


3Cu + 2Fe3+ 3Cu2+ + 2Fe


• Redox

• Obj: SWBAT describe how electrochemical cells use and produce electricity.

• Do Now: Write the half reactions for the following equation:

Cu + Ag+ Cu2+ + Ag

Electrochemical Cells

• Electrochemical cells = conversion of energy between electrical and chemical

• Voltaic (Galvanic) cell = SPONTANEOUS chemical energy electric energy

• Electrolytic cell = requires an electric current to force a NONSPONTANEOUS chemical reaction to occur

• SPONTANEOUS = NO ENERGY REQUIRED

• Electrode = site at which oxidation or reduction occur

• Anode = electrode where oxidation occurs

• Cathode = electrode where reduction occurs

• In a VOLTAIC CELL you need a SALT BRIDGE which allows for the MIGRATION OF IONS!!!!

Anode Cathode

Big RED CAT AN OX

REDuction occurs at the CAThode

ANode is the site of OXidation

• Electrons flow from ANODE TO CATHODE

• Voltmeter reads 0 Volts when it reaches equilibrium

• TABLE J

• Anode is on top, Cathode on bottom


• Redox

• Obj: SWBAT describe how electrochemical cells use and produce electricity.

• Do Now: Write the half reactions for the following equation:

Fe + Cu2+ Fe3+ + Cu

• Finish Review Packet

• Electrolysis = when electricity is used to force a chemical reaction to occur

• Used to obtain elements in groups 1, 2, and 17

• Used for electroplating (cathode is what is getting plated)

Anode

Cathode

Silver

Similarities between voltaic and electrolytic

• Both use redox

• Anode is site of oxidation

• Cathode is site of reduction

• Electrons flow from anode to cathode

Differences

• Redox is spontaneous in voltaic cell, but nonspontaneous in electrolytic cell

• Voltaic – Anode = (-)

– Cathode = (+)

• Electrolytic – Anode = (+)

– Cathode = (-)


• Redox

• Obj: SWBAT review electrochemical concepts as well as delve deeper into the explanations behind chemical reactions surrounding the transfer of electrons

• Do Now: Take out your homework and answer the following question: Explain the difference between the anode and cathode in a voltaic vs. electrolytic cell


• Redox

• Obj: SWBAT delve deeper into the explanations behind chemical reactions surrounding the transfer of electrons

• Do Now:

Mg + Cu2+ Mg2+ + Cu

What got oxidized? Reduced? What’s the reducing agent? Oxidizing agent?

Redox Test

• Grab zipgrade, reference tables, and exam from middle table

• WRITE YOUR NAME ON THE EXAM

• Start multiple choice at #46 (ends at 70)

• Write legibly

• Extra credit questions on the back (finish the test first)

• Only graders at lunch


• Redox

• Obj: SWBAT design a voltaic cell with the mission to provide the most possible amount of energy – Describe how chemical reactions can lead to an

electric current

• Do Now:

• Homework: Work on Project

Project • There’s been a zombie apocalypse and your group of

survivors needs the most effective battery possible (given all the metals from Reference Table J). You’ve been selected!

• Your design should include: • A list of the electrodes you would use, including which

would act as the anode and which would act as the cathode.

• A diagram of the battery you created, showing the flow of electrons through the system.

• The overall oxidation-reduction reaction of your battery, including oxidation states of each atom.

• The oxidation half-reaction of your battery. • The reduction half-reaction of your battery. • A written explanation of why you’ve chosen the

components of your battery that you have and a justification as to why these are the ideal components.

chemistry topic 9 › ourpages › auto › 2016 › 9 › 15... · 2017-05-31 · •chemistry –...

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