REDOX NOTEPACKET – 1

Mr. Dolgos Regents Chemistry

NOTE PACKET

Unit 10: Electrochemistry (Redox)

*STUDENT* * STUDENT *

REDOX NOTEPACKET – 2

UNIT 10: Electrochemistry (Redox)

Vocabulary:

Redox Reduction Oxidation Reducing Agent Oxidizing Agent Oxidation Number Half reaction

Electrode Galvanic or Voltaic Cell Salt bridge Electrochemical Cell Electrolytic Cell Anode Cathode

Unit Objectives:

x Define and identify oxidation reactions x Define and identify reduction reactions x Assign oxidation numbers to elements in a compound x Write and balance half reactions x Identify oxidizing agents and reducing agents x Distinguish between voltaic and electrolytic cells x Identify the components of an electrochemical cell x Indicate the direction of electrons and ions through an

electrochemical cell x Determine, using Table J, whether a reaction if spontaneous

or not

*STUDENT* * STUDENT *

REDOX NOTEPACKET – 3

REDuction – OXidation Reactions (AKA Redox): rxns that involve the _____________________________; both reduction and oxidation must happen ____________________! Reduction = ___________________ by an atom or ion; __________ ___________ goes ________/____________ Oxidation = ___________________ by an atom or ion; __________ ___________ goes ________/_____________ A way to remember Æ

L E O the lion goes G E R *Oxidation and reduction happen because of the __________ for electrons in a chemical reaction. Species prefer to either ________ or _________ electrons in a chemical reaction. AND

**Oxidation and reduction are __________ or __________________ reactions and one cannot happen without the other. If one atom _______ electrons, there must be another atom that will _______ electrons. Green Chunk Experiment: Example: ___ Al + ___ CuCl2 Æ ___ ___________ + ___ ______ Aluminum is above Cu on Table J so it will replace it! Notice how Al is all by itself (on left of arrow) with a zero charge and then bonded (on right of arrow) where it takes on a charge

REDOX NOTEPACKET – 4

IDENTIFYING REDOX REACTIONS One way that we can begin to identify a redox reaction is to inspect the _________________________ from reactant to product side (for every element involved in the reaction). Oxidation numbers are used to track the __________________________ (electron transfer) from reactant to product side of rxn Oxidation Number (State) = ____________, ____________, OR ____________ (_______) values that can be assigned to atoms; identify how many electrons are being lost or gained by an atom/ion when they ____________________ *top listed # to the upper right is the most common oxidation number for that element Trick 1: _________________________ reactions are always REDOX!

Ex: ___ Zn + ___ HCl Æ ___ _________ + ___ _________

*___/___ are by themselves on one side and bonded on the opposite side

Trick 2: DOUBLE REPLACEMENT REACTIONS are NOT REDOX! Ex: ___ NaOH + ___ HCl Æ ___ _________ + ___ _________

*charges stay the same for all elements in the rxn

REDOX NOTEPACKET – 5

Rules for assigning OXIDATION STATES (numbers):

1) _______________________________ (elements not bonded to another element) have an oxidation number of ________.

This includes any formula that has only one chemical symbol in it (single elements & diatomic elements). Examples: _______ _______ _______ _______

2) In _____________, the sum of the ____________ for all

elements must ____________________.

Ex: NaCl Ex: Mg3N2 Na: 1(+1) = +1 Mg: Cl: 1(-1) = -1 N: 0! 0! Ex: HNO3 H: N: O: 0!

* The ________________________ is the number ___________ the

_______________. It is the charge on _____ atom of that element! ** Trick: You can keep polyatomic ions together and use the charge from

Table E to determine the oxidation numbers for those elements. *** Remember that we almost always write the __________________

and the ___________________ in a compound formula. EXAMPLE: EXCEPTION to this rule:

REDOX NOTEPACKET – 6

3) ___________________ always have a ___ oxidation number when in a compound (bonded to another species). ___________________ always have a ___ oxidation number when located within a compound.

(Assign) Ox #:

Ex: LiCl MgCl2

4) __________ is always a ___ in compounds. The other __________ (ex: Cl, Br, I) are also ___ as long as they are the most electronegative element in the compound. (Assign) Ox #:

Ex: HF CaCl2 NaBr

5) _____________ is a ___ in compounds unless it is combined with __________ or __________________, in which case it is ___. (Assign) Ox #:

Ex: HCl LiH

6) _____________ is ________________ in compounds. (Assign) Ox #:

Ex: H2O

When combined with ___________ (__), which is more electronegative, ___________________.

(Assign) Ox #:

Ex: OF2

When in a __________________________. A peroxide is a compound that has a formula of ________.

(Assign) Ox #:

Ex: Na2O2 H2O2

7) The sum of the oxidation numbers in polyatomic ions must equal the ___________________________ (_________________).

Ex: Cr2O7

2- Cr: 2( ) = O: 7( ) = = (charge on ion)

REDOX NOTEPACKET – 7

A reaction is REDOX if…_________________________ _____________________________________________________ Reduction (GER) = ________________________ by an atom or ion; _________________________ goes _______/______________

Oxidation (LEO) = ________________________ by an atom or ion; _________________________ goes _______/______________

Assign oxidation numbers for all elements and complete the tables:

Example 1: C + H2O Æ CO + H2

Charge: Increases/Decreases e-: Lost/Gained Oxidized/Reduced C0 H+1

Example 2: MnO2 + 4HCl Æ MnCl2 + Cl2 + 2H2O

Charge: Increases/Decreases e-: Lost/Gained Oxidized/Reduced Cl-1 Mn+4

Oxidizing Agent (OA) = _______ that is _________; species that ________________________________

Reducing Agent (RA) = _______ that is __________; species that ________________________________

*NOTE: OA & RA are ALWAYS located on the __________________!

Assign oxidation numbers for all elements and identify the OA and RA:

Example: C + H2O Æ CO + H2 OA = ____ RA = ____

REDOX NOTEPACKET – 8

HALF REACTIONS Half reactions allow us to show the _________________________ in a redox rxn. For each redox reaction, we can illustrate two ____________________. One half-reaction shows ____________ and other shows ____________. Example of a Reduction Half Reaction: Fe3+ + 3e- Æ Fe

*Electrons on left hand side, __________ in the rxn (____). Notice also how the charge for Fe goes down from left to right, ____________ (____). Charge goes down because Fe __________ e-.

Example of an Oxidation Half Reaction: Fe Æ Fe3+ + 3e-

*Electrons on left hand side, _________ in the rxn (____). Notice also how the charge for Fe goes up from left to right, _____________ (____). Charge goes up because Fe _______ e-.

NOTICE: Always ____________________ to the side of rxn that has a

____________________ (remember: electrons are ___________!) FOLLOWING THE LAW OF CONSERVATION: 9 Half reactions follow the _____________________________. This

means that there must be the _______________________ on both sides of the reaction arrow.

9 There must also be a _____________________________. In half

reactions, the _________________________________________ of the equation, although it doesn’t necessarily need to equal zero.

REDOX NOTEPACKET – 9

RULES FOR SETTING UP HALF REACTIONS

1) Assign oxidation numbers to all elements in reaction 2) Draw brackets and identify oxidation & reduction 3) Begin to set up half reactions. Pull out brackets bringing element symbol

and assigned charge with you. Set up as a reaction with arrow connecting two sides that have different oxidation numbers assigned. Only trick: diatomics must be pulled out as a pair. This is the only time you ever “bring subscripts with you” in creating half reactions!

4) FOR REACTIONS INVOLVING DIATOMIC ELEMENTS ONLY: Balance mass 1st (make sure there are the same number of elements on each side of each half reaction)

5) Lastly, balance charge in each half reaction by inserting appropriate amount of electrons into each half reaction to attain conservation of charge. Always add electrons to side that has a more positive charge. REMEMBER, electrons are negative in nature! Net charges on each side of rxn should be equal after adding electrons. Assign oxidation numbers to all elements or polyatomic ions. Label the brackets for reduction (red) or oxidation (ox). Ex. 1:

Mg + ZnCl2 Æ MgCl2 + Zn OXIDATION Half Reaction: Mg0 Æ ______ + ______

REDUCTION Half Reaction:

Zn+2 + ______ Æ ______

REDOX NOTEPACKET – 10

Ex. 2 (balance masses):

Hg + I2 Æ HgI

OXIDATION Half Reaction (make sure to balance the masses):

______ Æ ______ + ______

REDUCTION Half Reaction: ______ + ______ Æ ______

Ex. 3 (balance charges):

Cu + AgNO3 Æ Cu(NO3)2 + Ag OXIDATION Half Reaction: ______ Æ ______ + ______

REDUCTION Half Reaction:

______ + ______ Æ ______

Now, we need to balance the charges:

___ x (Ag+1 + 1e- Æ Ag0) = ___Ag+1 + ___e- � ___Ag0

REDOX NOTEPACKET – 11

Table J and Spontaneous Reactions

General Rule: elements ___________ on Table J are ________ reactive than the elements below them Spontaneous rxn = rxn occurs w/out adding energy to system x If the “single” element is more active

than the “combined” element, the reaction will be spontaneous.

Non-spontaneous rxn = rxn will not occur unless energy is added to system x If the “single” element is less active

than the “combined” element, the reaction will NOT be spontaneous.

Complete the following equations by writing in the products formed or “no rxn” Ex 1: Zn + PbCl2 Æ Ex 2: Zn + BaO Æ Ex 3: Ca + CrF2 Æ Ex 4: Mn + NiS Æ Ex 5: Fe + MgI2 Æ Ex 6: Co + PbCl2 Æ

REDOX NOTEPACKET – 12

TWO TYPES of ELECTROCHEMICAL CELLS

1. Voltaic (similar to a battery) 2. Electrolytic (similar to alternator in cars)

SIMILARITIES BETWEEN THE TWO: x Both involve ___________ reactions; chemical reactions which

involve the flow of ______________ x Both involve the flow of __________________, or __________,

measured in _________ x Both have ______________ (conductive surfaces where oxidation

or reduction occurs); called the _________ and the _________ x _______________ or _______________ occurs in each half cell

RED CAT AN OX ______________________ ______________________ (__________________)

______________________ ______________________ (__________________)

x Electrons flow through the _______ from the _________ to the

_________.

REDOX NOTEPACKET – 13

Voltaic Cells x Cells that _____________________ convert _____________ energy

into ________________ energy or electric _____________. x ____________________ CATHODE

x The ______________________ of the 2 metals (Table J) x _______________________________________ to it x the _____________ electrode in a ______________________ x electrode where _______________ occurs (_____________)

ANODE x The ______________________ of the 2 metals (Table J)

x _______________________________________ to cathode x the ______________ electrode in a ______________________ x electrode where _______________ occurs (_____________)

Example 1: Wet Cell x ______________, are a form of ______________ battery

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/PbbatteryV9web.html

x Consists of LEAD ANODE and LEAD OXIDE CATHODE x Both electrodes immersed in a ________________ solution x Advantage: process is readily ____________ (by alternator) x Disadvantage: very ________, somewhat ______________

Example 2: Dry Cell

x _______________________ are the type of batteries in a portable radio, remote control, etc.

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/ZnCbatteryV8web.html

x CARBON (GRAPHITE) CATHODE surrounded by moist electrolyte paste

x Usually ZINC ANODE *SALT BRIDGE

x provides a path for the _________________ between the half-cells x prevents the __________________________

REDOX NOTEPACKET – 14

Voltaic Cells (a.k.a Galvanic Cells) http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

1. Use Table J to predict the direction that electrons will spontaneously

flow. Draw arrows to indicate the direction on the wire.

2. Based on your answer above, which would be the negative electrode and

which would be the positive electrode? ________________________

3. Explain your answer to #2. _________________________________

______________________________________________________

______________________________________________________

4. At which electrode or in which half-cell does reduction occur? _____

5. At which electrode or in which half-cell does oxidation occur? _____

6. Which electrode is the cathode? _____

7. Which electrode is the anode? _____

*Electrons don’t flow to the cathode, they flow through it to the ions in solution. That’s why the cathode never becomes negative.

REDOX NOTEPACKET – 15

Electrolytic Cells x Cells that use _________________ to force a ___________________

____________________________ to occur. x This process is for __________________ and ___________________

Example: _________________________ (keeps the car battery replenished with energy)

Electrolysis Experiment Animation (w/ tutorial): http://media.pearsoncmg.com/bc/bc_0media_chem/chem_sim/electrolysis_fc1_gm_11-26-12/main.html

Standard Hydrogen Electrode (Zinc) http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/SHEZnV7.html

Standard Hydrogen Electrode (Copper) http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/SHECu.html

Electrolysis of Water http://jchemed.chem.wisc.edu/JCESoft/CCA/samples/cca3ElecW03.html

CATHODE x electrode where _____________ are __________ x the ________________ electrode (opposite of voltaic cell) x electrode where _______________ occurs (____________)

ANODE x electrode where _____________ are _______________________ x the ________________ electrode (opposite of voltaic cell) x electrode where _______________ occurs (____________)

REDOX NOTEPACKET – 16

NOTICE: x There is ___________________. This is a forced chemical reaction. x You will always see a _______________ hooked up to an electrolytic

cell which drives the ____________________

1. Predict the direction that electrons will flow. Draw arrows to indicate

the direction on the wires.

2. Based on your answer above, which would be the negative electrode and

which would be the positive electrode? _________________________

3. Explain your answer to #2. _________________________________

______________________________________________________

______________________________________________________

4. At which electrode does reduction occur? ____________

5. At which electrode does oxidation occur? ____________

6. Which electrode is the cathode? ____________

7. Which electrode is the anode? ____________

REDOX NOTEPACKET – 17

Electrolysis of a Fused Salt x ________________ = ________________ = ________________ x ________________ is used to ________________________________

o Metals that are not found alone/uncombined in nature o ________________ and ________________ Metals

REDOX NOTEPACKET – 18

Compare and contrast the two types of electrochemical cells:

GALVANIC/VOLTAIC

ELECTROLYTIC

Flow of e- (spontaneous or

forced)

(+) electrode

(-) electrode

*Direction of e- flow

Reduction ½ cell

Oxidation ½ cell

*Direction of e- flow is either “Anode → Cathode” or “Cathode → Anode”

*Fuel Cells: galvanic cells for which the reactants are continuously supplied.

Hydrogen Fuel Cell Animation: http://www.lanl.gov/orgs/mpa/mpa11/animation.htm