Vimal Electrochemistry

7/29/2019 Vimal Electrochemistry

1/65

CHM 1020 Concepts inCHM 1020 Concepts inChemistryChemistry

An onAn on--line course for nonline course for non--majorsmajors


2/65

IntroductionIntroduction

A small cohort of UWF faculty completedA small cohort of UWF faculty completed

an intensive StudioE course presented byan intensive StudioE course presented bythe Academic Technology Center duringthe Academic Technology Center duringthe fall 2006 semester.the fall 2006 semester.

This presentation details an entire courseThis presentation details an entire coursedesigned in an ondesigned in an on--line format that wasline format that was

developed during this program.developed during this program.The course will be taught for the first timeThe course will be taught for the first time

during the summer of 2007.during the summer of 2007.


3/65

StudioE ComponentsStudioE Components

A course design matrix was used to:A course design matrix was used to:

zz establish student learning outcomesestablish student learning outcomeszz plan assessment instrumentsplan assessment instruments

zz

construct a course that incorporatesconstruct a course that incorporatesinstructional strategies which provide studentsinstructional strategies which provide students

with the opportunities to meet these goalswith the opportunities to meet these goals


4/65

Building an OnBuilding an On--line Course:line Course:

A Work in ProgressA Work in Progress PlanPlan

zz The course design matrix allowed us to:The course design matrix allowed us to:

Set major course goalsSet major course goalsSet weekly course goalsSet weekly course goals

Devise instructional strategies to meet the goalsDevise instructional strategies to meet the goals

Plan a general assessment strategyPlan a general assessment strategy

Build the onBuild the on--line courseline course Implement the course byImplement the course by

zz Presenting each sessionPresenting each session

zz AssessmentAssessment

EvaluateEvaluatezz Review student dataReview student data

zz Review the courseReview the course

zz Modify the courseModify the course


5/65

CHM 1020 OrganizationCHM 1020 Organization

The course is organized into fourteen modules.The course is organized into fourteen modules.

My intention is to introduce the modules earlierMy intention is to introduce the modules earlierthan necessary. For instance, students couldthan necessary. For instance, students couldaccess the following material on the Wednesdayaccess the following material on the Wednesdaybefore rollbefore roll--out.out.zz TheThe WelcomeWelcome information: Getting to Know You,information: Getting to Know You,

Orientation to OnOrientation to On--line Learning and Narrated Tour ofline Learning and Narrated Tour ofthe Textbookthe Textbook

zz The Course SyllabusThe Course Syllabus

zz Term Paper InformationTerm Paper Information

zz Module One including Chapters 1 and 2 PowerpointModule One including Chapters 1 and 2 PowerpointPresentations and suggested homework assignmentsPresentations and suggested homework assignments


6/65

FlowFlow

Each module consists of a PowerPointEach module consists of a PowerPoint

presentation, suggested homework assignmentpresentation, suggested homework assignmentand threaded discussion.and threaded discussion.

Chapters begin with a demonstration, introduceChapters begin with a demonstration, introduce

new concepts while reinforcing concepts seen innew concepts while reinforcing concepts seen inprevious modules, and wrap up with the theoryprevious modules, and wrap up with the theorybehind each demonstration.behind each demonstration.

There are 9 quizzes, one WebQuest, thirteenThere are 9 quizzes, one WebQuest, thirteenthreaded discussions and a term paper tothreaded discussions and a term paper toassess student learning.assess student learning.


7/65

Communication Routine andCommunication Routine and

Course Community BuildingCourse Community Building Communication between the students will beginCommunication between the students will begin

immediately with theimmediately with the Getting to Know YouGetting to Know You icebreakericebreaker

and will continue with weekly threaded discussions.and will continue with weekly threaded discussions. I will communicate with students in D2L through currentI will communicate with students in D2L through current

postings in thepostings in the NewsNews. The. The EventsEventscalendar will mirrorcalendar will mirror

the syllabus.the syllabus. Email office hours are posted in the syllabus and I willEmail office hours are posted in the syllabus and I will

use group mail to communicate with the class.use group mail to communicate with the class.

These avenues will provide students with opportunitiesThese avenues will provide students with opportunitiesfor feedback. I donfor feedback. I dont see these as onet see these as one--way streets.way streets.


8/65

Appropriate Tutorials and SupportAppropriate Tutorials and Support

ResourcesResourcesThis is one area that needs enhancing.This is one area that needs enhancing.

While I have provided students with links toWhile I have provided students with links tosome specific topics in the Merlot Learningsome specific topics in the Merlot LearningMaterials, the Wisconsin OnMaterials, the Wisconsin On--line Learningline Learning

Object Repository and the Vega Science Trust, IObject Repository and the Vega Science Trust, Iwould like to provide more.would like to provide more.

Their textbook has a site where they can obtainTheir textbook has a site where they can obtain

student resources such as onstudent resources such as on--line quizzes andline quizzes andadditional links of interest. See the narrated touradditional links of interest. See the narrated tourof the book.of the book.


9/65

The LessonThe Lesson

Chapter 11 Oxidation and ReductionChapter 11 Oxidation and Reduction

This chapter covers a classification of reactionsThis chapter covers a classification of reactionsknown asknown as redoxredox. These reactions are a result. These reactions are a resultof electron transfer between two substances.of electron transfer between two substances.

Content includes the exploration (application),Content includes the exploration (application),an interactive website, definitions and theoryan interactive website, definitions and theory(text and graphics).(text and graphics).

Opportunities for interaction include theOpportunities for interaction include thedemonstration, questions throughout thedemonstration, questions throughout thePowerPoint and threaded discussion.PowerPoint and threaded discussion.


10/65

Chapter Eleven

Assignments


11/65

Recommended Homework

Self Assessment Quiz On-Line at the Publishers Sitewww.wiley.com/college/snyder

Homework Problems Chapter Eleven Questions 1, 2, 6, 8, 10, 12, 14, 16,

18, 20, 26,

2003 John Wiley and Sons Publishers
http://www.wiley.com/college/snyderhttp://www.wiley.com/college/snyder


12/65

Chapter 11: Oxidation and Reduction

The Electricity of Chemistry

Courtesy Craig Aurness/Corbis Images


13/65

Oxidat ion-Reduct ion

z AKA Redoxfor shortz Both processes always occur together! For

every substance oxidized, another is reduced.z They are in evidence everywhere around us

and can be beneficial such as when thereduced form of food is converted to energy torun our bodies or detrimental such as wheniron rusts to form iron oxides.

z Reduced forms such as food are high inenergy. Oxidized forms such as rust are low inenergy.


14/65

Things t ha t Go Boom !

z The group 1 alkali metals are extremely

reactive. Their reactivity increases as we godown the group from lithium to cesium. Whenthese metals (M) react with water, the general

oxidation-reduction reaction is:2 M + 2H2OH2 + 2MOH

Check out the next website (warning: the

language is slightly offensive)http://video.google.com/videoplay?docid=-

2134266654801392897&q=alkali+metals






2134266654801392897&q=alkali+metals






2134266654801392897&q=alkali+metals
http://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metalshttp://video.google.com/videoplay?docid=-2134266654801392897&q=alkali+metals


15/65

Explora t ion

z Assemble a glass, bleach, vinegar, tincture of iodine (I2) and

galvanized nails (nails covered with a thin layer of Zn to preventcorrosion.

z Add tacks to a glass followed by tincture of iodine (purple incolor). Let stand and the color fades [Zn2+(aq) is colorless].

I2 + Zn Zn2+ + 2 I-z Pour the yellow or colorless solution into another glass. Add a

few drops of bleach and the dark purple (I2) returns.

H2

O + ClO- + 2I- I2

+ Cl- + 2OH-

z Vinegar can be added if clumps [ insoluble Zn(OH)2] form. Thisresults in a clear, intensely colored purple solution.

Zn(OH)2+ 2 CH3COOH Zn2+ + 2 H2O + 2 CH3COO-



16/65

Galvanized tacks, drugstore iodine, and household bleach.

Courtesy Ken Karp



17/65

Figure 11.1: Color changes with galvanized tacks, iodine, and household bleach.

Courtesy Ken Karp



18/65

Figure 11.1: Color changes with galvanized tacks, iodine, and household bleach.

Courtesy Ken Karp


19/65

I See t he L ight !

z Inside the flashlight, the flow of electrons is the electriccurrent. When turned on, we complete the circuit, allowingelectrons to flow and lighting the flashlight bulb.

z The circuit is the path that electrons follow in an electric circuit.z See the inside of a carbon-zinc flashlight battery. As the

electrons leave the zinc casing, the zinc becomes Zn2+with the

loss of 2 negatively charged electrons.z Flashlights contain dry cells. These are called primary

batteries. The reactions are irreversible and deadbatteriesresult.

z

Batteries can consist of a series of electrochemical cells.z In an electrochemical reaction electrons are produced which

can flow from one location to another. Electrochemicalreactions can also be produced by this flow of electrons.



20/65

Figure 11.2: A flashlight battery.

Courtesy Eveready Battery Company, Inc.


QUESTION


21/65

What element forms the metal casing of a

common flashlight battery? Name three

compounds (other than water) that form the

black paste held within this metal casing. Whatelement forms the porous rod embedded in

this paste?

QUESTION


22/65

Elec t roc hem ic a l Ce l l

z An electrochemical cell is a cell or battery that

produces electricity from chemical reactions.

z Oxidation-reduction reactions can be used toproduce electricity and we find them inbatteries and dry cells.

z The passing of electrons resulting from a redox

reaction through a circuit yields energy (achemical change produces electricity; potentialenergy converts to kinetic energy).


23/65

One Pot a t o , Tw o Pot a t o

zThe two-potato clock is a low currentclock driven by an electrochemical cellconstructed of two potatoes and wires

connected to strips of zinc and copper.z Any electrolyte (conductor of electricity)

will do in place of the potatoes. It is theidentity of the zinc and copperelectrodesthat is important.



24/65

Figure 11.3: A clock run by a chemical reaction.

Courtesy Skilcraft


25/65

Daniel l Cel l

z The Daniell cell consists of a container of Cu2+solution

with a copper electrode and a container of Zn2+

solutionwith a zinc electrode. The electrochemical cell consists ofseparate compartments connected by a wire or voltmeter(reads 1.1 volts) and a porous barrier which functions as

a salt bridgeand allows ions to flow through it.Cu2+(aq) + Zn (s) Zn 2+(aq) + Cu (s)

blue solution silver colorless reddish

colored solution metal

metal accumulates

dissolves



26/65

Figure 11.4: A form of the Daniell cell.

Courtesy Ken Karp


QUESTION


27/65

Would a Daniell cell work equally well if thesalt bridge were replaced by a length of

copper wire? Explain.


28/65

Oxidat ion-Reduct ion

Three View s

z There are three views of oxidation-reduction. In the

classic sense, when a substance was oxidized, oxygenwas added to it. The substance was the reducingagent. When a substance lost oxygen, it was reducedand is the oxidizing agent.

z Oxidation = gain of oxygen atomsz Oxygen environments are oxidizing.

z Reduction = loss of oxygen atoms

z

4 Al + 3 O2

2 Al2O3oxidized reducedreducing agent oxidizing agent


29/65

Sec ond View

z Oxidation is the loss of hydrogen atoms.

z Reduction is the gain of hydrogen atoms.

z H2 is a reducing environment.

z C2H4 + H2 C2H6reduced oxidized

oxidizing agent reducing agent


30/65

Thi rd V iew

z We have become more sophisticated in our interpretation

and can evaluate the electrons transferred in a redoxreaction even if oxygen (or hydrogen) isnt gained or lost.

z To do this we must evaluate the oxidation states of allspecies in balanced reactions and assign them as

oxidizing and reducing agents.z The number of electrons lost by one species is equal to

the number of electrons gained by another.

z Oxidation is loss of electrons.

z Reduction is gain of electrons.


31/65

Ox idat ion Num bers

z Oxidation is the loss of electrons. The oxidation number becomesmore positive (for example +2 becomes +3) or less negative (-2 goes

to -1).z Reduction is the gain of electrons. The oxidation number becomes

less positive (+3 goes to +2) or more negative (-1 goes to -2).

z OIL RIGmakes the processes easier to remember. Oxidation is lossof electrons. Reduction is gain of electrons.

z Oxidation numbers correspond to the actual charges on an ion. Pureelements are assigned an oxidation number of zero.

z Cd0 (s) + Ni2+(aq) Ni0 (s) + Cd2+(aq)oxidized reduced

becomes becomesmore positive less positiveReducing agent Oxidizing agent


32/65

Revis i t ing t he Danie l l Cel l

Cu2+(aq) + Zn0 (s) Zn 2+(aq) + Cu0 (s)

blue solution silver colorless reddishcolored solution metal

metal accumulates

dissolves

The Cu2+(aq) becomes less positive. It gains two electrons and isreduced to Cu metal. It is the oxidizing agent.

The Zn (s) is oxidized. It loses two electrons and is oxidized toZn2+. It is the reducing agent.


33/65

One Com par t m ent Redox

React ions

z Take two beakers, put CuSO4 (an electrolyte whichdissociates into Cu2+and SO

4

2- ions) and a Zn strip inBeaker A. Put ZnSO4 (an electrolyte which dissociatesinto Zn2+and SO4

2- ions) and a Cu strip into Beaker B.z No change occurs in beaker B.z Beaker A has the same reaction and observations as the

separate compartment Daniell cell.z Two half-cell reactions can be written which represent the

oxidation and reduction processes.

Reduction half-cell reaction shows the gain of electrons:Cu 2+(aq) + 2 e-Cu0 (s)

Oxidation half-cell reaction shows the loss of electrons:Zn0 (s)Zn 2+(aq) + 2 e-



34/65

Figure 11.5: Zinc metal and copper sulfate.

Courtesy Andy Washnik



35/65

Figure 11.6: Zinc metal in copper sulfate solution.


QUESTION


36/65

We can infer that copper ions in water produce

a blue color by noting that a solution of coppersulfate in water, which contains copper ions

and sulfate ions, is blue and that a solution of

zinc sulfate in water, which contains zinc ionsand sulfate ions, is colorless. Why does this

observation lead us to conclude that the

copper ions of the copper sulfate solutionproduce the blue color?


37/65

Daniel l Cel l

z The half-reactions take place in their separate compartments.Electrons flow through the wire from Zn plate (anode) to the Cu

plate (cathode). The sulfate ions do not take an active role inthese reactions.

z Ions move through the salt bridge, complete the circuit andelectricity flows. Ions move through the salt bridge to maintain

electrical neutrality. Cations migrate towards the cathodereaction. Anions migrate towards the anode reaction.z The copper electrode gains weight and the solution gets lighter

in color.z The zinc electrode loses weight.

z The electron flow can be used to light a light bulb connected inthe circuit or run a motor. It can do work. It will continue as longas reactants (Zn and Cu 2+) are available.



38/65

Figure 11.7: Chemical and electrical changes in the Daniell cell.


QUESTION


39/65

Suppose that as the zinc metal is converted

into zinc ions (which are soluble in water) allthe copper ions in solution are converted to

copper metal. What new compound, a

combination of a cation and a balancing anion,would then exist in the colorless solution?


QUESTION


40/65

The reaction of calcium and chlorine

described in Section 3.12 can be rewritten as

Ca + Cl2 CaCl2. In this reaction, what isbeing oxidized? What is being reduced? Writereactions for the two half-cells of this redox

reaction.


QUESTION


41/65

We prepared the salt bridge of our Daniell cell

by soaking a strip of cloth in a sodium chloridesolution. As the cell begins to operate, would

you expect the sodium and chloride ions of

the bridge to move? If your answer is yes,which direction would the sodium ions move

an in which direction would the chloride ions

move? If your answer is no, explain why not.


42/65

Vol t z The volt (V) is the unit of electrical potential; the pressure that moves

electrons from one point to another. The Daniell cell produces 1.1 V.

The electrons pass through the wire or meter with a force of 1.1Vmoving from the zinc strip to the copper strip.z A useful analogy is the pressure of water through pipes. The greater

the water pressure, the greater the force that moves the water alongthe pipe from point A to point B.

z It is named after Alessandro Volta who described the first electricalbattery, the Volta pile in 1800.z The amp or ampere is the unit of electrical current which measures the

rate of flow of electrons. A useful analogy is a comparison with ameasure of gallons per minute which is used to measure the flow of

water.z To be hazardous to humans, the combination ofboth high voltage and

high amperage is necessary.



43/65

Alessandro Volta demonstrating his discovery to the French Academy in 1801.

Courtesy Culver Pictures, Inc.


QUESTION


44/65

By increasing the areas of the zinc and copper plates

in the Daniell cell, we can increase the amperage ofthe current flowing through the circuit without

affecting the voltage we measure with the voltmeter.

How does increasing the size of the zinc and copperplates affect the electrical pressure that moves the

electrons along? How does increasing the size of the

plates affect the rate of flow of the electrons through

the circuit?

O id t i d R d t i


45/65

Ox idat ion and Reduc t ion

Potent ia ls

z Reduction potential is the voltage produced or

required for the addition of electrons to anatom or ion.

z Oxidation potential is the voltage produced or

required for the removal of electrons from anatom or ion.

z In the Daniell cell the Zn atoms have a greateroxidation potential than the Cu atoms and theCu2+cations have a greater reduction potentialthan the Zn2+cations.


46/65

St andard Reduc t ion Pot ent ia l z The standard reduction potential is the value of the reduction potential of a

substance compared to the reduction potential of the hydrogen ion at roomtemperature (25C) and specific ionic concentrations. The reduction potentialof hydrogen is defined as zero volts. Other species are set relative to hydrogen. 2H+ + 2 e-H2 0.00 V See Table 11.1 for standard reduction potentials

z The more negative the value, the stronger the reducing strength and the half-cell reaction will go as written.

z The more positive the value, the stronger the oxidizing strength. The half-cellwill have to be reversed when writing a balanced redox reaction. When areaction is reversed, the sign of the potential changes from positive to negativeor negative to positive.

z Potentials dont change when the numbers of atoms, molecules or electronsinvolved in the reactions change. The oxidation of fluoride ion is the same

(-2.87 V) whether 2 moles or one mole of F- is oxidized.



47/65

Figure 11.8: Reduction of two hydrogen ions to a hydrogen molecule.

2003 John Wiley and Sons PublishersQUESTION


48/65

Which element, atom, molecule, or ion in Table

11.1 is the strongest oxidizing agent? Which is

the weakest?



49/65

What is the most powerfulreducing agentin

Table 11.1? Explain.


50/65

Use of Table 11.1

z The table can allow us to calculate the

resulting voltage of an electrochemical cell(two half-cell reactions) and to predict if theredox reaction will be spontaneous.

z In order for the redox reaction to bespontaneous, the sum of the two half-cellpotentials must be positive.

z If the sum is negative, the reverse reaction will

occur. If the sum is negative, the reaction canbe take place as written if there is an externalsource of energy such as a battery.



51/65

In section 10.2 we saw that acids liberate hydrogen

gas when in contact with certain metals, such as iron

and zinc. Using the data in Table 11.1, show that the

reactions of iron, and zinc with an acid spontaneously

generate hydrogen gas by redox reactions. Identify

three other metals that will spontaneously liberatehydrogen gas from an acid. Identify three metals that

will not.



52/65

Using Table 1.1, predict which, if any, of the

following metals will decolorize tincture ofiodine: (a) nickel, (b) copper, (c) silver, (d)

magnesium, (e) calcium? Explain your answer

for each.

I2 + 2 e-2I- Potential = +0.54 V


53/65

Energy versus Rat e

z You can use Table 11.1 to determine the energy releasedduring a spontaneous redox reaction. Theelectrochemical potential indicates the amount of energy.

z This information does not tell you the rate at which achemical reaction will occur. This information is obtained

by studying the kinetics of reactions.z Some spontaneous reactions that release a great deal of

energy occur very slowly. Some such as the reaction ofsodium metal with chlorine gas (4 Volts) occur very

rapidly.



54/65

Using the half-cell reactions of Table 11.1,

write the redox reaction that would release thegreatest amount of energy. That is, write the

redox reaction that produces the greatest

redox voltage.


55/65

Bat te r ies

z Batteries work because their construction

allows electrons to flow spontaneously fromreducing agents to oxidizing agents.

z Real batteries are constructed of safe,

convenient, long-lived and economicalmaterials with high voltages.

z Real batteries are constructed of diverse

materials including carbon-zinc, alkaline,lithium, mercury, silver oxide and nickel-cadmium.



56/65

The Daniell cell itself isnt used as a

commercial battery. Suggest at least onereason why it isnt.


57/65

Car Bat t er ies

z The rechargeable lead-acid battery is the most commonautomobile battery. A 12-V lead storage battery in a caris a series of 6-2V cells. They have been in use forapproximately 150 years.

z The lead anode (oxidized) is the part of the battery that

allows electrons to flow through an external circuit.z The lead dioxide, PbO2, cathode (reduced) receives the

returning electrons.

z The two sets of plates are immersed in a sulfuric acid

solution.


QUESTION


58/65

What change takes place in the composition of

the battery fluid the liquid that bathes thebatterys plates as the battery is recharged

by the generator or alternator?


59/65

Elect ro lys is

z Batteries can provide electrical energy to producechanges that dont occur spontaneously.

z Electrolysis is the use of electricity to decompose asubstance into its component parts.

z Water doesnt spontaneously decompose to form oxygen

and hydrogen gas. However if a source of electricity suchas a battery and inert electrodes (platinum) are immersedin water, hydrogen and oxygen gas can be generated.

2 H2O (l)2 H2 (g) + O2 (g)



60/65

Figure 11.10:The electrolysis of water.

Courtesy Yoav Levy/Phototake


QUESTION


61/65

What three chemicals are produced through

the electrolysis of sodium chloride solutions?What three chemicals would you expect to be

produced by the electrolysis of a solution of

sodium bromide?


62/65

Redox in Everyday L i fe

z Because we live in an oxygen-rich

environment, oxidation occurs naturally.Metals corrode or rust.Galvanizing is a process that provides a

protective Zn coat to metals.Galvanic or bimetallic corrosion is the

corrosion that results when two different

metals are in contact with a separatingelectrolyte layer.


QUESTION


63/65

What is galvanizedmetal? Describe two ways

galvanizing helps keep iron from rusting.


64/65

Com m on Ox id izing Agent s

z Hydrogen peroxide (H2O2). When 6-12% solutions are used onhair, it lightens dark pigments to colorless products. This is asimilar mechanism for all bleachessuch as sodiumhypochlorite (NaOCl). Hydrogen peroxide is also used as a 3%solution as an antiseptic.

z

Potassium dichromate (K2Cr2O7) is an orange solution which isa component of the Breathalyzers to detect for alcoholconsumption. The Cr6+ is reduced to a green Cr3+and alcoholis oxidized to an aldehyde. The degree of color change

indicates the amount of alcohol consumed.z Chlorine (Cl2) in drinking water acts as a disinfectant and kills

bacteria.


65/65

Com m on Reduc ing Agent sz Metals can be obtained through reduction or reaction with

a more active metal which is oxidized.

z Photographic developer is a reducing agent whichreduces colorless Ag+to black silver metal (Ag0). Theunexposed silver is removed and the negative image

remains which is then made into a positive print.z Antioxidants such as Vitamins C, E and A.

z Hydrogen gas reduces ores to form metals. It is alsoused to process organic compounds. For instance

ethylene can be converted to ethane by the addition ofhydrogen across the double bond. Hydrogen is also usedin the production of ammonia from nitrogen gas.

Documents

Vimal Electrochemistry