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REDOX NOTEPACKET – 1

Mr. Dolgos Regents Chemistry

NOTE PACKET

Unit 10: Electrochemistry

*STUDENT* * STUDENT *


UNIT 10: Electrochemistry (Redox)

Vocabulary: Redox Reduction Oxidation Reducing Agent Oxidizing Agent Oxidation Number Half reaction

Electrode Voltaic Cell Salt bridge Electrochemical Cell Electrolytic Cell Anode Cathode

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

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

or not

*STUDENT* * STUDENT *


REDuction – OXidation Reactions (AKA Redox): rxns thatinvolve 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

L E O the lion goes G E R

*Oxidation and reduction happen because of the __________ forelectrons 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 ___ ___________ + ___ ______

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

Lesson 1:


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 commonoxidation number for that element

Trick 1: _________________________ reactions are always REDOX!

Example: Zn + HCl ___ _________ + ___ _________

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

Trick 2: DOUBLE REPLACEMENT REACTIONS are NOT REDOX!

Example: NaOH + HCl ___ _________ + ___ _________

*charges stay the same for all elements in the rxn

Lesson 2:


Rules for assigning OXIDATION STATES (numbers):

1) _______________________________ (elements not bonded toanother 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 allelements 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:

Lesson 2(con't):


3) ___________________ always have a ___ oxidation numberwhen in a compound (bonded to another species).___________________ always have a ___ oxidation numberwhen 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 mostelectronegative 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 equalthe ___________________________ (_________________).

Ex: Cr2O72- Cr: 2( ) =

O: 7( ) = = (charge on ion)


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- Fe *Electrons on left hand side, __________ in the rxn (____).

Notice also how the charge for Fe goes down from left toright, ____________ (____). Charge goes down becauseFe __________ e-.

Example of an Oxidation Half Reaction:

Fe 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:

Half reactions follow the _____________________________. Thismeans that there must be the _______________________ on bothsides of the reaction arrow.

There must also be a _____________________________. In halfreactions, the _________________________________________of the equation, although it doesn’t necessarily need to equal zero.

Lesson 4:


RULES FOR SETTING UP HALF REACTIONS

1) Assign oxidation numbers to all elements in reaction2) Draw brackets and identify oxidation & reduction3) Begin to set up half reactions. Pull out brackets bringing element symbol

and assigned charge with you. Set up as a reaction with arrow connectingtwo 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: Balancemass 1st (make sure there are the same number of elements on each sideof each half reaction)

5) Lastly, balance charge in each half reaction by inserting appropriateamount of electrons into each half reaction to attain conservation ofcharge. Always add electrons to side that has a more positive charge.REMEMBER, electrons are negative in nature! Net charges on each sideof 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 MgCl2 + Zn

OXIDATION Half Reaction:

Mg0 ______ + ______

REDUCTION Half Reaction:

Zn+2 + ______ ______


Ex. 2 (balance masses):

Hg + I2 HgI

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

______ ______ + ______


______ + ______ ______

Ex. 3 (balance charges):

Cu + AgNO3 Cu(NO3)2 + Ag

OXIDATION Half Reaction:

______ ______ + ______


______ + ______ ______

Now, we need to balance the charges:

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


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

If the “single” element is more activethan the “combined” element, thereaction will be spontaneous.

Non-spontaneous rxn = rxn will not occur unless energy is added to system

If the “single” element is less activethan the “combined” element, thereaction will NOT be spontaneous.

Complete the following equations by writing in the products formed or “no rxn”

Ex 1: Zn + PbCl2

Ex 2: Zn + BaO

Ex 3: Ca + CrF2

Ex 4: Mn + NiS

Ex 5: Fe + MgI2

Ex 6: Co + PbCl2

Lesson 5:


TWO TYPES of ELECTROCHEMICAL CELLS 1. Voltaic (similar to a battery)2. Electrolytic (similar to alternator in cars)

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

involve the flow of ______________Both involve the flow of __________________, or __________,

measured in _________Both have ______________ (conductive surfaces where oxidation

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

RED CAT AN OX______________________ ______________________ (__________________)

______________________ ______________________ (__________________)

Electrons flow through the _______ from the _________ to the_________.

Lesson 6:


Voltaic Cells Cells that _____________________ convert _____________ energy

into ________________ energy or electric _____________. ____________________

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

ANODE The ______________________ of the 2 metals (Table J)

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

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

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

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

Example 2: Dry Cell _______________________ are the type of batteries in a

portable radio, remote control, etc.http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/ZnCbatteryV8web.html

CARBON (GRAPHITE) CATHODE surrounded by moistelectrolyte paste

Usually ZINC ANODE

*SALT BRIDGE provides a path for the _________________ between the half-cells prevents the __________________________


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.

Lesson 7:


Electrolytic Cells Cells that use _________________ to force a ___________________

____________________________ to occur. 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 electrode where _____________ are __________ the ________________ electrode (opposite of voltaic cell) electrode where _______________ occurs (____________)

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

Lesson 8:


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

cell which drives the ____________________

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

mr. dolgos regents chemistry note packet unit … notepacket – 1 mr. dolgos regents chemistry note...

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