CHEM 30

Recharging A Battery Reverse Net Redox EquationWhen you charge a secondary cell the net redox reaction equation is the reverse reaction.Lead-Acid Battery

PbO2(s) + SO42-(aq) + 4H+(aq) +2e- PbSO4(s) + 2H2O(l)+Pb(s) + SO42-(aq) PbSO4(s) +2e- PbO2(s) + 2SO42-(aq) + 4H+(aq) + Pb(s) 2PbSO4(s) + 2H2O(l)DischargingChargingLets Set The StageFor centuries now, ever since the first gasoline powered vehicles were invented there has been a drive to find a cleaner energy source.

Ever since the electric powered car was invented in 1888, it has drifted in and out of popularity for various reasons.

Mostly because of limitations like:Battery LifePower (Top speed)Power (Step on the pedal and go)

These problems have all been solved btw.Gasoline Vs Electric CarsGasoline engines are about 20% efficient..so that means that 80% of the energy in the gas you buy is lost and pollutes the environment.By comparison electric cars are around 90% efficient.Gasoline powered engines require regular maintenance to stop problems resulting from the incomplete burning of gasoline.Electric engines require very minimal maintenance to replace things that would need replacing no matter what type of car you have.

Gasoline Vs Electric CarsThe extraction of fossil fuels causes huge amounts of pollution.In fact, the CO2 pollution created by the extraction of fossil fuels in Alberta is equal to the amount of CO2 produced in the rest of Canada.

The electricity that electric cars use is often produced by burning fossil fuels anyway.But youd have a hard time finding anything in your house that is 90% efficient.Did I mention that electric engines are almost silent?Gasoline Vs Electric CarsLets Put This In PerspectiveSo you go and fuel up your ride.its a 60 L Tank.Lets say gas is $1.20/Lits a pretty good average.So it costs you ($1.20/L)(50L)= $60.00So gasoline engines are 20% efficient

That means that out of the $60.00 to gas up you car/truck you only actually use $12.00 of it.$12.00!$48.00 just floated off as pollution.Pollution that you will eventually pay(again) to get rid of.

So Why Arent We Using Electric Cars?Well because their less efficient.

Because their ugly.

Because they arent ready yet, too many problems, the technology doesnt exist yet

Their too slow, we have places to be.

The batteries to run the car are too heavy and not powerful enough.85% vs 20%...right.How a car looks has little to nothing to do with the engine.The first electric car was invented in 1888!Electric Car vs Porsche 911 TurboElectric Cars Are BetterThe BatteryThe Electric Cars Ball and ChainThe biggest obstacle stopping the wide spread use of electric cars is the lack of a powerful, lightweight, and inexpensive battery to power it.

The old Lead-Acid battery (The big klunker you put in your caryouv probably all seen them) is:Too HeavyToo WeakDoesnt last long enoughExpensiveThe Battery ProblemDesigning A Battery For The FutureDesigning a new battery that is lightweight, inexpensive, powerful, and long lasting would make electric powered vehicles far, far, far, farrrrrrr superior to gasoline powered vehicles.

So how do we do?How does a battery work?If were going to make a new battery we kind of have to know how one works in the first place.

***A battery stores/creates electricity through a redox reaction.***The Lead-Acid BatteryLets Make The Redox Equation+ Pb(s) + PbO2(s)Sulfuric Acid and Lead Battery. Hint: Lead and Lead OxideH2SO4(aq) H+(aq)+ SO42-(aq)+ H2O(l)The Lead-Acid BatteryLets Make The Redox Equation+ Pb(s) + PbO2(s)Sulfuric Acid and Lead Battery.H+(aq)+ SO42-(aq)+ H2O(l)OARARAOASOASRAThe Lead-Acid BatteryLets Make The Redox Equation+ Pb(s) + PbO2(s)H+(aq)+ SO42-(aq)+ H2O(l)OARASRASOAPbO2(s) + SO42-(aq) + 4H+(aq) +2e- PbSO4(s) + 2H2O(l)Pb(s) + SO42-(aq) PbSO4(s) +2e- RechargingTaking Reactants and Creating Redox EquationsTo this point you have learned how to do all the steps of taking chemical reactants and creating an oxidation and a reduction .

Even more than that, you can add the two together and get an overall equation.

What this unit is about, is taking that knowledge of redox reactions and using the Electrical Potential E (V) values from your data booklet.Allesandro Volta invented the first electric cell.

Allesandro was inspired by another scientist that noticed that when he electrocuted a frogs leg it twitched.Who said electrocuting random stuff doesnt help you learn.

You know what this means right!!?

+

=

Google Images of Learning

Voltas Electric Cell

Electrolyte solution (Salt Water/NaCl)Metal rods are referred to as the electrodes or poles (+) and (-).(-)(+)Positive(+) pole is called the cathode.

Negative(-) pole is called the anode.CathodeAnodeElectrons flow from the Negative pole (Anode) to the positive pole (Cathode).The flow of electrons is called Electricity.Voltas Electric Cell

Electricity created from the flow of electrons from one pole to the other was so small that it wasnt enough to be useful.

Solution?Voltas Electric Cell

An electric cell does not conduct electricity unless the poles are connected together.

The Car Battery

The Battery broken in 6 cells connected together in a chain.Volt Meter

The Volt Meter measures the electric potential difference between the cathode and the anode.The size of the battery doesnt necessarily mean its voltage is higher.

Bigger batteries can store more energy and transfer more at one time.Ammeter An ammeter measures the flow of electrons.

Bigger batteries can have the same voltage as smaller batteries, but because their bigger they can send a higher volume of that potential energy at one time.

Larger volume per time means that the rate of flow from a big battery is higher.

Amperage (ammeter unit) is a measure of the rate of electron flow.1 Amp = 1 Coloumb/second

Voltage is the electric potential difference between the two poles. Measures the difference between how many electrons are at the anode and how many are at the cathode.

Voltage is specific to the type of battery, IT IS NOT AFFECT BY THE SIZE OF THE BATTERY!

You can get a 1.5 Volt battery in any size; AAA, AA, C, D whatever, size doesnt matter.

Voltage, Coulombs, AmperageVoltage

Coulomb is a measure of the amount of energy stored in a battery.

Coulombs are expressed as Q..a measurement of energy only.

How many coulombs of energy is dependant on the size of the battery. LIKE THE VOLUME OF A BATTERY.Voltage, Coulombs, AmperageCoulombs

800 Coulombs

2 CoulombsAmperage is the rate/speed at which electricity can flow out of the battery.

Amperage is the amount of electrons/second.

Amperage is Coulombs/second.Voltage, Coulombs, AmperageAmperage

4 amps or 4 C/s.

0.55 amps or 0.55 C/s.Voltage, Coulombs, AmperageThe Water Tank/Hose Analogy

115L Liter Hat Water Tank

11350 Liter Water TankVoltage is determine by the type of reaction.

Since both tanks hold water so the voltage is the same for both.

Coulombs are a measure of amount, volume in this case......115L vs 11350L.

Amperage is the rate.Which would have a higher rate of flow?

Batteries

The Zinc-Chloride battery.

One of the most common and inexpensive batteries.

Invented in 1865.The common 9V D cell battery is made up of 6 seperate cells.1.5V1.5V1.5V1.5V1.5V1.5V9 VBatteries that are sealed and cant leak are called dry cells.2 Types of CellsPrimary Cells: A electric cell that cannot be recharged, once the chemicals in the batter react to produce electricity it can never be reversed.

Secondary Cells: An electric cell that can be recharged. The chemical reaction that occurs to produce electricity can be reversed if electricity is applied to the cell.

Nickel-CadmiumLead-AcidLithium-IonZinc-ChlorideCarbon-ZincMercury-Mercury OxideFuel Cells40-70% EfficientOperate in the exact same way as a primary electric cell.

You put fuel into the cell (the fuel can be anything that will react to produce electricity) just like you put reactants into a batterywhich are used up (cant be reversed) just like a primary electric cell.Except!In a fuel cell, its not sealed and you continuously put fuel into it, adding more as it get consumed by the reaction.A fuel cell never runs out and dies like a battery.As long as you keep adding fuel, it keeps going.Hydrogen-Oxygen Fuel Cell70% Efficient

O2O2H2H2H2OH2OO2H2(OH-)ForwardCouple Other OptionsAluminum-Oxygen CellIndustrial Fuel Cells_

_

_

_

_

_

_

_

_

_

_

_

Possible use in electric cars.Replaceable solid aluminum fuel.High energy density.

3 moles of electrons released for each Al.Aluminum is light weight.Replace aluminum every 2500km.Same as small scale but no volume weight concern.Need longer lifetime of fuel in cells.Almost always co-generation units.Produce electricity AND heat.90% efficient!

Produce 400 Mega Watts!A galvanic/voltaic cell is the same as the electric cells we have looked at so far, but the two electrodes are in two different electrolytes.

They split up an electric cell into two reactions so they can examine each reaction (oxidation/reduction) more closely.

The two cells are connected together by a salt bridge.

There are still two metal electrodes which need to be connected by an external (wire) for the cell to function

or Galvanic CellsCopper-Zinc Voltaic Cell

Shorthand Notation

First Electrode(s) Electrolyte(aq) Electrolyte(aq) Second Electrode(s) Cu(s) Cu(NO3)2(aq) Zn(NO3)2(aq) Zn(s) = Phase Change (s)-(aq)= Salt BridgeDescribing Voltaic CellsSo far we can describe how a voltaic cell has:

2 Electrodes (solid poles).2 Electrolytes.related to the electrode.Two electrodes are connect together with a wire.The two beakers (solutions) are connected together by a salt bridge.

But how do we know which pole is the anode and which is the cathode?

Describing Voltaic CellsWell, SOA undergoes Reduction at the Cathode.

The SRA undergoes Oxidation at the Anode.

Well thats useless information.how can we tell where oxidation and reduction are happening?Whats the SRA?Whats the SOA?

To determine SOA and SRA the process is the same as when you predicted redox reactions last unit.

The Ox and The CatEasiest way to remember this stuff is the following analogy.

An Ox

Red Cat

xidationnodenoitcude

edohtaSOASRADetermining The SRA/SOA

Lets Try One

***Remember! The Na+ and NO3- are part of the salt bridge and are spectatorsso dont list them as species present.

Determining The SRA/SOA

Determining The SRA/SOA

SOA undergoes Reduction at the cathode (+V).

The SRA undergoes Oxidation at the anode (-V).CathodeAnodeLets Try One

AnodeCathodeVoltaic Cell Summary

Inert ElectrodesUsually the electrodes (solids) used in a voltaic cell are related to the electrolytes used.

Exp:Cu(s) for Cu2+(aq) ElectrolyteAg(s) for Ag+(aq) ElectrolyteCu(s) for Cu(NO3)2(aq) ElectrolyteZn(s) for Zn(NO3)2(aq) Electrolyte

But there are powerful oxidizing and Reducing agents that arent related to any solid formwhat electrode do you use then?Inert ElectrodesStrong oxidizing agents such as Manganate (MnO4-(aq)) or Chromate (Cr2O72-(aq ))which react in acidic environments (with H+) cannot form permanently solid (insoluble/Do not conduct electricity) electrodes.

The reason why so often the electrolyte and electrode are related is because the electrolyte ions reduce at the same rate as the solid electrode oxidizes.

1:1 2:2 3:3 Ratio between the electrons transferred.The most common inert electrode is C(s).C(s) = Carbon.also called GraphiteInert Electrodes C(s).

Inert electrodes DO NOT REACT with the electrolyte.

Inert electrodes are 100% spectator species.

Inert electrodes only purpose is to provide an attachment for an wire to be connected to each pole so e- can flow between them.

Standard Cell PotentialsStandard Cell Potential (E) is the maximum electric potential difference between the cathode and the anode.

E specifies that the cell is under specific SATP conditions and the electrolytes each have an EXACT concentration of 1.0 mol/L.

Voltaic Cell

ElectrodesElectrolytes

Calculating Standard Reduction PotentialsWe know the Standard Cell potentials of all the possible oxidation and reduction reactions.

Standard REDUCTION potentials are the difference between the cathodes Standard Cell Potential and the anodes SCP.

FORMULA:Hint: All those numbers down the side of the Reduction table in your data booklet, yah, thats them.

Calculating Standard Reduction Potentials So we know the formula for calculating the standard reduction potential of a cell:

There isnt some magical machine that measures these values. So where do they come from?***THEY COMPARE ALL OTHER OAs AND RAs TO HYDROGEN AS A ZERO MARKER.***They just use Hydrogen=Zero as a reference point and rate their E values relative (stronger/weaker) to it.

SAME AS WHEN YOU MADE A REDOX TABLE EARLIER.

But how do they get these + and numbers on the table in the book???Calculating Standard Cell Potentials (Easy)You have to write the standard cell notation.Find the SRA(anode1/2) and SOA(cathode1/2).Use the Standard Reduction Potential Formula to calculate the number.

**Inert Electrode** Do we have to write it? NO.SOASRA

52Calculating Standard Cell Potentials (Hard)

You have to write the standard cell notation.Find the SRA(anode1/2) and SOA(cathode1/2).Use the Standard Reduction Potential Formula to calculate the number.

Zn2+(aq)

Cu2+(aq)

SRASOA

0.34 V (-0.76 V)

+ 1.1 V53Lets Practice What We KnowA Combined Question

In order to write the equations of what reaction is happening at the cathode and anode we need to find out the SRA and SOA.So..?Page 7: Reduction/Standard Electrode Potentials Table.

SOASRALets Practice What We KnowA Combined QuestionAs soon as you have found the SOA and SRA, you list their half-reactions Exactly as they appear in the table.

SOASRASOA:SRA:Sn2+(aq) + 2e- Sn(s)Cr(S) Cr2+(aq) + 2e- CathodeAnode

-0.14 V (-0.91 V)

+ 0.77 VSn2+(aq) + Cr(S) Sn(s) + Cr2+(aq)

Corrosion Case Study(P.634-636)Electrolytic Cell: A cell in which the reduction and oxidation reactions that occur within it ARE NOT SPONTANEOUS.

When you calculate the Standard Cell Potential (E) of an electrolytic cell it is a negative (-V).If you looked at this cell and found the SOA and SRA, the SOA would be lower on the redox table than the SRA.Again this would tell you it was not spontaneousThus an electrolytic cell instead of a voltaic cell which is spontaneous.Voltaic vs Electrolytic Cells

So..Its not Spontaneous? SoWhy Even Make An Electrolytic Cell If Nothing Happens?So in general a electric/voltaic cell starts with reactants which spontaneously react together to form products and electricity.

Electrolytic cells work the same way, except!As we know, they are not spontaneous, you have to supply energy to get them to go.***So you can think of an electrolytic cell as the reverse of a voltaic cell.***

So.Like We said, Why?So weve already mentioned that electrolytic cells are the opposite (reverse) of voltaic cells.How could this be useful?Voltaic makes products and electricitySo then electrolytic would need electricity but would make?....

***Electrolytic cells are especially useful for producing pure elements (the pure reactants in many voltaic cells that are expensive metals that are hard to find).***

Using Electrolytic Cells/Electrolysis

What was the problems that needed to be fixed?Interesting Info; Dates, Names, %s, $, other interesting tid bitProduction of AluminumAllowed aluminum production to be done at 1000C

The Chloro-Alkali ProcessRefining of MetalsWhy was it useful to use electrolysis?Aluminum has a melting point of 2072C, It would melt anything you put it in. Needed another way.Charles Hall, Paul Heroult, Al2O3, Na3AlF, Cryolite, $45,000--$0.90/KgNeeded cheap and easy to make chlorine.Cheap and easy way to make chlorine, could use hydrogen by product as fuel.95% of Chlorine made this way and 100% of NaOH made this way.Needed to purify metals from impure Ores. VERY PUREIt produced super pure metals and used impurities to pay for it.Converts 99% pure ores into 99.98% pure. ElectroPlating (P. 650)You Summarize and ShareGroup 1: Group 2:Group 3:Group 4:Group 5:Group 6:Group 7:Group 8:Group 9:Group 10:

Cell stoichiometry like the stoichiometry you have done previously deals with the amounts of certain species in a reaction.

The amounts of different species are still related to each other on a molar level.aka need mols, and once you have mols you use the balancing coefficients R/G or N/G.

How can we calculate electrons?Theres no formula to count number of electrons.We could use R/G and find out mols of electrons if we know about other species in the reactionBut what do we do if we dont know about the other species?

m=nMn=m/Mm=nMn=CV?R/GCalculating n of ElectronsWell, we know electricity is the flow of electrons.Well water flows.How can we calculate how much water flows out of a hose?

WellHow fast its flowing times How long.right?Amount = Rate X TimeHow about counting cars?How do you calculate how many cars drive by in a day?

A= Rate X Time

A= (Cars/hour) X (# of Hours)Using Flow To Measure ElectronsQ= ItQ is the number of coulombs (# of e-)I is Ampshow fast the electrons flow(Rate)t is the amount of time the electrons have to flow. So we can calculate the # of electrons.

But how many electrons is their in a mol?OkSo How Many Electrons In A Mol?Ok, so far we have found out how to calculate how many electrons are present by using:

So we need to find the mols of electrons to do stoichiometry..So how many electrons does it take to make of mol of e-?

Usually when we get an amount (g or e-s in this case) we divide it by the molar mass to find moles.

Is there a molar mass for electrons? (e-)

Michael Faraday

Michael FaradayAKA; Handsome DevilAs a kid Michael taught took it upon himself to teach himself chemistry. No classes or anything just learned it...

Once he had learned chemistry he got himself a job as a chemists assistant.

Studies gasesDiscovered BenzeneElectrolysisElectric MotorsGeneratorsTransformersNot bad for no education..but come one who teaches themselves chemistry in their spare time!?A strongly religious man that firmly believed that science should only be used to helpnever to kill.Angel?Hmm, I wonder how he would feel about his science being used for the electric chairFaradays Constant (F)The Molar Mass of e-Through Faradays experiments with electricity he managed to calculate the atomic mass of an electron.

The atomic mass of an electron e- is:

Molar Mass = 9.65 x 104 Coulombs/mol

Once we have the atomic mass of an electron we can then convert any flow of electricity into mols of electrons.**Also called Faradays Constant**

Q (C) 9.65 x 104 C/mol= ne-

ItOnce you calculate ne- the rest of the stoichiometry is the same as before. nG(R/G)= nRAfter you have mols of required all thats left is converting that mols into the units the question asks for.

***Make Sure***Be careful that you calculate the units the questions asks for..sometimes you dont need mols.you need to stop at coulombs.

In which case you just calculate Q.so just (I)(t)