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by: Brady Spinka


Marketplace > University of Texas at Austin > Chemistry > CH 302 > PRINCIPLES OF CHEMISTRY II
Brady Spinka
GPA 3.98

David Laude

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David Laude
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This 25 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 302 at University of Texas at Austin taught by David Laude in Fall. Since its upload, it has received 8 views. For similar materials see /class/181873/ch-302-university-of-texas-at-austin in Chemistry at University of Texas at Austin.

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Date Created: 09/07/15
Lecture 12 Solving buffer and neutralization problems Deriving the Buffer Equation You have had it hammered into your head that there are three simplified equations that can be used to calculate proton or hydroxide concentration in acidbase equilibria o the strong acid and base equation 0 the weak acid and base equation 0 the buffer equation You have seen the strong and weak cases now it is time to derive the buffer equation But first what is a buffer Very simply a buffer is the mixture of a weak acid and conjugate base or a weak base and conjugate acid Recall that the word conjugate means that the pair differs by a single proton For example acid base Buffer Example 1 Acetic acid Sodium acetate Yes weak acid and base differ by one proton HC2H302 NaC2H302 Example 2 Ammonium ion ammonia Yes weak acid and base differ by one proton NH4 NH3 Example 3 Hydrochloric acid Chloride No strong acids and their cases can t be buffers HCl Cl39 Example 4 Carbonic acid Carbonate ion No the acid and base differ by two protons H2CO3 CO3 Derivation of the buffer equation using the RICE expression We start with the general case of a acid equilibrium HA Hl A39 with Ka Hl A39 HA and then construct a RICE expression with the following steps Start with Ca for the amount weak acid HA and Cb for the amount of the conjugate weak base We assume OM is the amount of strong acid Hl to start Since Qlt K the reaction shifts right so we add signs to the change array accordingly Assume that X is the concentration of protons that forms Doing the math at equilibrium the concentrations are Cax X and Cbx respectively LIIJme Reaction HA H A lnitial C a 0 C 1 Change X X X Substituting these amounts into the equilibrium expression we get Equilibrium C a x x C b x Ka X CbX CaX But now we make an important approximation As mentioned above by definition weak acids and their conjugate bases don t dissociate very much typical values are maybe one out of a thousand or out of ten thousand This means that x which is Hl is very small relative to the starting concentration And in steps 6 Let X PF and then K Hl C b H C a H 7 Approximate that Hl is very small because this is a weak acid doesn t dissociate so C a H Ca 8 Similarly C b H Cb 9 Now simplified we can rearrange the expression to obtain our famous result for the buffer equation H Ka CaCb Just as with the weak acid case what we have done is turn a quadratic equation into a simple BUFFER problem we can do in our head by using approximation that weak acids and bases don t dissociate very much which is true because that is the definition of a weak acid or base Wow anyone can derive the buffer equation With it let s solve a simple buffer calculation Example What is pH of a 01 M acetic acid and 01 M sodium acetate solution if Ka leO393 Note we have acetic acid which is a weak acid acetate which is a conjugate base 9 this means we have a buffer solution and can work the buffer equation So use buffer equation Hl K CaCb 1x105 010 1 1x105 and pH5 Note that Hl Ka for a buffer Also note that for buffer equation to work same conditions for Ca Cb and Ka apply 1 Ca and Cb must be large 2 Ka in 10394 to 103910 range Neutraliz ation We move on to more sophisticated acid base equilibrium problems that require an additional step to find equilibrium concentrations Note that to this point the only chemical equilibria associated with our acid base problems assuming KW was negligible were the simple weak acid or weak base cases HA Hl A39 In which the the K value is so small that basically nothing is happening in solution But what happens if we were to add strong acid or base to a solution containing various other acids and bases Now there is going to be a reaction that essentially goes to completion because the K value for strong acids and bases is essentially infinity in this course This reaction is referred to as a neutralization reaction and must be accounted for before finding equilibrium concentrations of the remaining materials For example what happens when I put an Hl or OHquot in solution Each of them look to react Hl looks for most basic thing in solution when hydroxide is present Hl OHquot 39 H20 with lots of heat released and if no OHquot then the protons look for weak base Hl Aquot 39 HA a little heat and if no Aquot is present then the proton attaches to H20 and makes a hydronium ion H3O Hl H20 gt H3o Similarly OHquot looks for most acidic thing in solution when protons are present Hl OHquot 39 H20 with lots of heat released and if no Hl then the hydroxide look for weak acid HA OHquot 39 Aquot H20 a little heat Let s watch cartoon pictures of neutralization in action as protons are added to a beaker containing weak base Beginning with four weak bases Aquot we will add a proton at a time watch a neutralization reaction happen and then determine what the resulting equilibrium solution contains I l r0t0ns added to a beaker of four A39 no Hl added so only Aquot in solution this is the weak base case and we use OHquot Kbe12 four Hl added so now H and Aquot are equal and total neutralization occurs This is called the equiva ence point and with only HA left we solve it with the weak acid equation Hl KaCa Case 4 add ve protons to a beaker with four A39 so neutralization must occur five Hl added so now H is in excess after neutralization occurs We assume that the H 1s a strong acid is much more important than the weak acid and ignore the weak acid So we perform the calculation of H concentration using the strong acid equation So how important is it to be able to perform a neutralization Incredibly important Note thatl will give you a siz step procedure for performing acid base reactions Right in the middle of those siX steps is the need to look for and perform a neutralization reaction If you can learn to perform neutralization reactions acid base chemistry becomes pretty simple It will allow you to perform sophisticated problems involving buffer neutralization and all kinds of titrations But if you don t learn to do the neutralization step every acid base problem no matter how easy will be a challenge The Five Neutralization Reactions And as a parting treat here are the five possible neutralization reactions if you use the symbols I taught you for acid base chemistry Strong acid neutralizing strong base H OH39 2 H20 Strong acid neutralizing weak neutral base H B BH Strong acid neutralizing basic salt of weak acid H A39 2 HA Strong base neutralizing weak neutral acid OHquot HA Aquot ignore the water left over Strong acid neutralizing acid salt of weak base OHquot BH B ignore the water left over Note that it isn t hard to learn these Just remember three things 0 There is always a strong acid or base in the problem 0 It is always paired with a conjugate acidbase pair in the reaction 0 Always make sure your mass and charge balance if you are not sure what goes where CH302 Random Musings February 17 2009 Post V Day special 1 First my apologies for falling behind on email and postingsia combination of illness an infected computer and losing internet service has slowed my normal process for posting and responding I will do my best to catch up but be aware that I have now posted the notes from the Sunday review on my web site under the lecture link 2 There is a first exam coming up on Wednesday evening I have provided the question types for it below and had a review on Sunday night A format and procedure for exam 1 as well as the question types are found at the end of the musings But some highlights of ways in which the exam procedure may be different than last semester The exam will be Wednesday evening from 730 till 930 pm You get 120 minutes sharp Room locations Last name AK will be in Welch 2224 Last name LO will be in Welch 3502 Last name PZ will be in WCHogg 1120 You will be given a sheet of equations and constants and a periodic table You may bring a calculator A makeup exam will be given on Sunday evening from 6 to 800 pm in Welch 2224 Physical Equilibria 16 calculating equilibrium concentrations from K 1 temperature dependence of phase changes 17 determining reaction direction from Q and K 2 vapor pressure theory 18 LeChatelier and reaction direction 3 salt dissociation in water 19 LeChatelier and reaction direction 4 phase diagram interpretation 20 Van t Hoff equation and T dependence of K 5 phase diagram navigation 21 relationship of AG to K 6 calculating AH across phases transitions 7 gas solubility in liquids Introduction to Water Equilbria 8 ranking miscibility of liquids 22 theory of autoprotolysis of water 9 Clausius Clapeyron equation 23 temperature dependence of Kw 10 Van t Hoff factor and colligative properties 24 molar solubility calculation ranking solubilities based on Ksp values converting between pH pOH H and OH 11 colligative property application 12 colligative property calculation NN GNU 13 colligative property calculation 27 ranking acidity and basicity from Ka and Kb 28 strong acid or base calculation Chemical Equilibria 29 weak acid or base calculation 14 setting up K from equilibrium expression 30 weak acid or base calculation 15 appreciating the magnitudes of K 3 Quiz 2 Results Travis informs me that you all earned an average score of 70 for Quiz 2 I have not had a chance to look at the question by question break down but will and will get back to those of you who had questions or concerns about the quiz 4 Travis is going to hold a review session tonight from 6 to 7 in WCHogg 1120 the lecture hall right underneath my office I hear he gives a pretty good review 5 Not that you even want to think about it but Worksheet 6 on buffers neutralization and titrations will be posted this weekend 6 Extra credit will be comingiI am already being queried about extra credit There will be three extra credits for this class each worth 1 of your grade Brie y they will include emailing me about teaching a science hater some chemistry over spring break attending a scholarly lecture in a eld that interests you and attending an undergraduate research poster session Much more to come 7 The ChemPortal folks are supposed to have ovemighted the 45 gift cards to me With any luck I will see them shortly and can return them to the students who purchased a onesemester option for the Portal Sorry for the delay but I have to imagine I will have these to you next week 8 Poetry Comer First three poems that have been written about this class at the interface between Valentine s Day and the exam on equilibrium After that the raw aching poetry of science and engineering students in love Most of them make me squirm with their unabashed sentiment But I promised so here they come The Chemistry to Hating Valentine s Day Anonymous I woke up Valentine s morning pushed open the door To run to my computer and check out my score For last Wednesday I took DrLaude s test I was sure I aced it I did my best But then I saw it on my computer screen out of180points I scored less that 115 I am not too happy so get the hell out ofmy way This stupid score ruined my Valentine s Day I mean it was multiple choice How hard could it be I thought at the very most I d miss only three But there were some questions a little too raw like which one is least true ofthe ideal gas law You see the word least could be open to debate but the tests have been graded so it s probably too late So to end this poem myfriends I have to say That because ofchemistry I truly hate VALENTINE S DAY A poem after failing the equilibrium exam At the start ofthe semester about four weeks ago we were all learning chemistry extremely very slow But now thatpace has changed and its no longer review for on that last equilibrium test I scored a 122 For that one evil satanic test is one with which I must cope because asfar as exempting thefinal I can kiss goodbye to all my hope And then I thought Hey maybe with extra credit my grade is saved then Laude announced to everyone NO EXTRA CREDIT IN YOUR EXEMPTION GRADE As my smile turned into afrown and my bubble began to burst I thought to myself well it can t get any worse For nothing can be worse than taking the final as my only grade andI can t blame Dr Laude since this grave is one I made Thefinal is around the corner and there are many things to yet be read I won t be able to sleep very much I lljustpass out near my bed So fellow classmates What can you learn from this rhyme Get o your lazy and stuay You re running out oftime Ode on CH302 Oh Dr Laude how you hate the fall and those trips with your daughter to be a model at the mall but stillyou love it and your family too and all ofyour students in chem 302 you love travis his ipod and the UGTAs as well and especiallyqu boy isnt shejust swell but acids and bases really make mefrown and asking ifthings shift left or right when the pressure goes way down so valentines day is a day oflove foryou andyour schooling but i think quotcan iget anAquot who am ifooling And now the raw aching poetry of science and engineering students in love For Mary Martha Intermingled Souls Who is worthy for to sing your praise M y feeble tongue knows not su icient words Nor any creature save seraphim may raise A song to tell the world of our love A warm mahog ny crown my fingers brush And sparkling blue green stars do mine eyes meet As the softness of your skin receives my touch Just so your tender heart does greet my soul Infull embrace I hold it now to me That though we are apart you feel my warmth And til your blissful countenance I see So you holdfast to me my void to bear Thus it is39 our souls intermingled be And so shall stay unto eternity Sometimes I wish you were mine Under your bedroom window I pray Someday you ll love me And we ll share a home one day Never a day goes by Love with you doesn t cross my mind I stare at you every day No not that creepy kind Now my love has been professed By Clausius Clapeyron Marshmallow Pillow Talk I heard the secret language of the marshmallow yesterday I listened to him cry I heard his mating Call for graham cracker planks and chocolate bar sidekick as his consistency transformed from a non tacky rubbery state to fused orgasmic sticky bliss Yes this Rare Event too caught me by surprise as I did not know who made that sound or why But then everything made sense the marshmallow was lonely no more His transmutation takes place not just by himself but with his very subtle call he Beckons the shield of cracker to help compress aMetamorphosis with his chocolate counterpart to that of the blessed Smore This sound this noise will catch you off guard one day when you ask yourself What it may be But it could be you see the sweet pillow talk of a marshmallow not lonely anymore To Silly Love your baby Untitled You can t go from hairy ice cream to idiotic circles without the kiwi in the middle The crazily happy and happily crazy to see you ilove is a simple thing A dangerous thing Pleasure full and painful like repetitively poking at a purpled bruise and hearing me laugh Chance F ate but who could love a beast The nal petal falls in the grace of ultimate peace A fairytale ending lives in the roots of our dreaming tree Where drops of rain shimmer beneath the starry sky What is love The vestigial of questions echoes down the corridors of time leaving naught but ambiguities love is putting on pajamas fresh from the dryer running through the grass and feeling green between my bare toes and you following suit thereafter the first hug after a week s vacation the white feathered wings of our imagination It is the color oflight and holds no shape The warmth that fills the caverns of my being Love is smelling your scent while you breathe my breath Waking up with you as my first thought and every night hearing dream sweet my love Embedded in our memories and our spirits It is the beat ofour hearts that will out tick all clocks Those days following in which we spent I hate to say but those are when I missed you I missed you a lot But days keep passing And with them my feelings But still is left Is remembering that I was happy Those amber eyes Re ected things in which you saw in me Even if I myself couldn t see That which you thought of me But why can t you see Your life is full it is full of fantasy Full of Romance and Ecstacy So you cannot forsee But that happiness is found in the black and bleak And chasing this tricky nancy Will end your ight of fancy By Romanticism with a capital R Self reflection on a Winter39s Night She was like night and day A beauty that knew no right or wrong What was her downfall was to be her crown Armed with words that cut through air and a heavy angry mind She never served her proper time Queen of life itself She was my queen My muse that knew only stealth She stole my heart and ate it while I slept So when I woke all I knew was the pit ofher gut And in that gut my heart ate away her soul And in her dreams she drank water from a bowl For not one day did my lovefor her I doubt and for everyday there on I swear I loved that xmx always or at least until the day she xxxx me out We re taught to think that love is beautiful that it transcends our bodies that it heals our souls And even though we don t know what this love thing is we come to associate it with concepts like cozy fireplaces on winter nights like holding hands in apple orchards like coming home to a personi your person But most of all we associate it with a feeling of forever We re told that love is everlasting consistent permanent Love is growing old and wrinkly together And if you find that kind of love you become one of the lucky ones The ones who have someone to come home to More often then not though love is eeting transient impermanent It comes and goes like waves in the ocean or ripples in fields of grain Sometimes it comes and lasts for mere moments or days or weeks or months or years But when it leaves if it leaves you re left wondering if it was ever really there It was quotDo They Collidequot Darling you used to take me to a place Somewhere that we could go to fade away We lie beneath the stars then face to face Without a care in the world come what may The world revolved yet time stood still Here we with each and ev ry twist and bend Would sleep and dream knowing our future s will To stay loving and faithful til the end Yet now I lie awake alone and cold You held my world and shattered it bit by bit Did it make you feel safe secure and bold Or have you in turn been condemned by it Though this beaten heart suffers endless strains Forgiveness edges in and love remains I wish there was something I could say Simple and precise that I could mean in everyway The three words mean so much And to everyone s heart it does touch People use it more than it is meant They use it without the usual intent You don tjust say it to anyone But to the only person you will ever love When you say it to family or to a friend Itjust doesn t mean the same in the end That love is unconditional and is known even without words You never have to say it because in their heart it is heard No this that I want to say Is not the I love you as a friend kind of way I mean it from way down deep inside Where the things that no one else knows lie I have never said this to anyone But since I meet you I knew you were the one Basically what I am really trying to say Is that I love you in every single way She s everything to me Heather Almost two decades ago I came into this world With someone who looked just like me We ve lived the same life We ve both held on tight To the one we both know we can t live without My twin Who has my same curly hair Is about to go on her own way She doesn t know it And I never show it She s everything to me Stacy must have the prettiest hair That I ve ever seen It is so fair If you don t believe me you are a square It would be completely my err To believe it looks like a mare And to do that I wouldn39t dare Whenever I see her all i can do is glare Her mother is beautiful to be her heir I wish I were pretty I ve resorted to prayer She should make it a tourist site and charge fair She would be more famous than Ric Flair One time she cut it and gave me quite a scare Ithought my own eyes out I would tear Some of her leftovers she did share I pasted it to my head as if to wear But it would not stick to me I swear She doesn39t even have underwear Stacy does have the prettiest hair im the groove you the estella you dora im the explora im the soul you the body you the cola im bacardi s im the music you the party you the song im the writa im the gas you the ignita you the playa im the game im the picture you the frame you the college im the dorm im the rain you the storm you the rose im the thorn im hope you the forlorn you the beat im the heart im the race you the start im the gazer you the star im the tenda you the bar you the book im the reader im the bird you the feeder im the ball you the roll you the crook my heart you stole CH 302 Exam 1 Procedures Format and Administration Exam format 1 A major CH302 exam covering the first nine lectures on chemical and physical equilibria will be administered Wednesday February 17 from 730 till 930 pm note the 120 minute length The exam will be worth 180 points Only problems similar in content and difficulty to those from quizzes and worksheets will be included on the exam Many of the problems are more challenging than the quiz questions 2 Test structure The exam will consist of 30 questions with each question worth 6 points Questions are in a multiplechoice format Look below for an exact breakdown of problem types 3 In addition to the problems you will be provided a bubble sheet a table of the elements and a list of useful equations and constants Plenty of space for working problems is provided on the exam Do not bring your own scratch paper Exam Administration READ THIS CAREFULLY IF YOU DO NOT FOLLOW PROCEDURES YOU MAY NOT BE ALLOWED TO TAKE THE EXAM The supreme rule for my exams everyone has the right to an optimum testtaking environment I am less concerned with cheating than I am with you making life miserable for others taking the exam All of the rules for this exam are constructed with this in mind 1 Exam location Last name AK will be in Welch 2224 Last name LO will be in Welch 3502 Last name PZ will be in WCHogg l 120 If you go to the wrong room you will not be allowed to take the exam There is only enough seating for the students as listed above 2 Exam start time 730 pm We may decide not to administer the exam to late arrivals if it becomes too disruptive to those taking the exam Once you start the exam you may not leave to take the makeup You must turn in scantron with validated identity 3 What you may bring to your seat for the exam number 2 pencils calculator I don t care what kind you bring something to drink What you may not bring to your seat anything else including coats food back packs books paper Walkmans If you must bring them to class place them at the bottom of the class room before the exams begins 4 During the exam the TAs will be available to answer questions Raise you hand and one of us will come to help you as best we can Do not leave your seat unless you are finished and are leaving the room 5 When you leave do so quietly AS YOU LEAVE YOU MUST SHOW YOUR UT IDENTIFICATION when you turn in your exam Make sure your name special code and SSN are bubbled in 6 Exam finish time 930 pm You will be given fair warning that the exam is about to end so you can start guessing on questions you don t know I WILL NOT TOLERATE ANYONE WRITING AFTER YOU ARE TOLD TO PUT DOWN YOUR PENCILS Anyone who is observed to be writing on their exam after the exam ends will be assumed to be cheating and will receive a 0 for the exam and will face additional academic penalties READ THIS AGAIN IF YOU DON T UNDERSTAND I WILL NOT TOLERATE ANYONE ANSWERING QUESTIONS AFTER THE EXAM STOPS AT 930 PM 7 If all goes well the exam scores will be posted by Thursday morning Please don t hassle us it they are not up right away We are doing our best 8 If you have any special considerations please contact me immediately by email so we have documentation 9 Responsibility There is an increasing tendency for you to think you can be irresponsible and mommy or daddy will take care of you in class I am not your daddy So your decision to show up unprepared for quizzes and exam without sharpened pencils or a calculator is not my problem I will have some pencils and some calculators available because the lower diVision of ce is nice and I will look after folks whose batteries die But if the collection of calculators I bring to class runs out you are on your own Grow up he said gently Lectures 23 and 24 Chemists and Chemical Engineers Make the World a Better Place Catalysts and Batteries Lecture 23 Two Famous Catalysts As we discussed when examining the Arrhenius equation K A exp EaRT one important factor in the rate of reaction is the activation energy The larger E the smaller k and the slower the reaction One of the thriving areas of research in chemistry is the search for ways to speed up reactions without increasing temperature which is expensive Lowering the Ea with catalysts is one approach Catalyst 3 de nition A material that speeds a rate of reaction by lowering the activation energy through a change of reaction mechanism Catalysts do not show up in the overall chemical reaction they are typically conserved to react over and over One class of catalysts are homogeneous catalysts which react in the same phase as the chemical reaction of interest For example a homogeneous catalyst is a liquid catalyst in a solution gas catalyst in the gas phase A really important area of research is with heterogeneous catalysts The catalysts are in a different phase than the overall reaction usually a solid For example solids are common heterogeneous catalysts for gas and liquid phase reactions Two famous catalysts The hole in the ozone catalyst Chlorine radical is a homogeneous catalyst that is reducing the size of the ozone Chloro uorocarbons are bad because they are volatile and typically find their way into the atmosphere There they undergo photolytic degradation photons from the sun break bands CF3CZ Lag CZ from sun The Clo then participates as a catalyst in a reaction that eliminates ozone 03 N t Cl Reaction 03 02 dd3 not mechanism O 0 02 show up in the overall Overall 03 O a reaction reaction The cleaner burning car catalyst Catalytic converters in cars are heterogeneous catalysts They are high surface area porous solids that do at least two things An oxidation 9 CO gtCO2 convert CO to CO2 A reduction 9 NOX gtN2 convert nitrogen oxides to nitrogen NO X Magical out N 2 heterogeneous catalyst in CO gt CO Note that the mechanism is not provided here just know there is a heterogeneous catalyst What are in the catalytic converters Current generation automotive catalyst material consists of a ceramic or metallic substrate coated by an various combinations of aluminum oxides mixed with rare earth oxides and metals like platinum Pt Pd Rh Lecture 24 Famous Batteries Having finished up redox reactions note that the ones we are interested in are those that make useful things like batteries In fact a batter is simply a couple of redox half reactions that can be put together so that E is positive and some work can be done So as you consider the electrochemical cell conventions below understand that they are useful in helping to describe the following kinds of famous batteries And while they don t get a lot of press batteries make our increasingly mobile world go round and there is an enormous amount of energy that goes in to finding redox reactions that among other things produce a lot of energy produce a lot of current don t weigh very much or take up much space aren t toxic or environmentally dangerous have reversible reactions are rechargeable oh and don t cost very much Over the years a lot of progress has been made and for example these days people walk around with 5 to 10 batteries on their person and don t even know it One thing is sure the ability to make small inexpensive power sources for our mobile world will be what drives changes in society So here are some batteries everyone should know g E 5 g E s Listedbelow 39 39 39 39 ii H i ll Primary Alkaline battery Used in common Duracell and Energizer batteries The electrodes are zinc and manganeseoxide with an alkaline electrolyte Inside an alkaline hathWV w A u A 39 ions The hydroxyl ions then react with zinc to form zinc oxide and water releasing electrons The electrons move toward the carbon rod and ow out around the circuit producing an electric current The battery stops producing electricity when all the manganese di xide is used up uncair battery 7 Lightweight zinc air batteries are small nonrechargeable batteries with open circuit voltages of 115 to 14Vper cell 39 39 L A Line air 39 39 39 39 in small devices such as hearing aids and pagers Secondary Batteries Rechargeable Lead acid battery Used in automobiles the electrodes are made of lead and leadoxide with a strong acidic electrolyte They are rechargeable Despite having the second lowest energytoweight ratio next to the nickeliron battery and a correspondingly low energytovolume ratio their ability to supply high surge currents means that the cells maintain a relatively large powertoweight ratio This along with their low cost makes them ideal for use in cars as they can provide the high current required by automobile starter motors Each cell contains in the charged state electrodes of lead metal Pb and lead IV oxide PbOz in an electrolyte of about 37 599 Molar ww sulfuric acid H2504 393 Separator Anode grid Cathode grid Nickel cadmium battery Uses nickelhydroxide and cadmium electrodes with potassiumhydroxide as the electrolyte Rechargeable Until recently virtually all rechargeable batteries were nickelcadmium NiCd usually pronounced quotnicadquot Although very dependable they need to be discharged fully before you charge them up or the amount of charge they will store and their effective lifespan can be greatly reduced Nickel metal hydride battery Rapidly replacing nickelcadmium because it does not suffer from memory effect Rechargeable type of rechargeable battery similar to a nickelcadmium NiCd battery but has a hydrogenabsorbing alloy for the anode instead of cadmium Like in NiCd batteries nickel is the cathode A NiMH battery can have two to three times the capacity of an equivalent size NiCd and the memory effect is not as significant However compared to the lithiumion battery the volumetric energy density is lower and selfdischarge is higher Applications of NiMH type batteries includes hybrid vehicles such as the Toyota Prius Lithium ion battery Very good powertoweight ratio often found in highend laptop computers and cell phones Rechargeable High discharge rates don39t significantly reduce its capacity nor does it lose very much capacity after each cycle still retaining 80 of its energy capacity after 500 recharge cycles Early versions were prone to exploding in the labs and people still claim there is a risk with these batteries Lecture 14 Wrapping up pH calculations with a sure re stepwise process for working problems If we make the right assumptions about K values far apart and concentrations large then we can apply approximations so that there are only six equations needed to solve acid base problems Even better there are only ve variables to consider in using these equations Ka Kb H OH C acid C base So there isn t a lot of complexity at the bottom of this The hard part is guring out which equation to use and what each of the variables is To accomplish this task we use the following procedure 1 strip away all the extraneous information spectator ions 2 identify strong acids and bases 3 identify weak acids and bases 4 determine if you should neutralize 5 perform neutralization calculation 6 decide whether to work the problem as an acid or a base Once these steps are done the problem is greatly simpli ed to the point that you can use the table above to work a calculation The back of this page shows every possible type of starting conditions and how they reduce to one of the problems above 1 Getting rid of spectator ions Always eliminate the ions that do nothing all alkali metals and alkali earths NaT KT CaH and all conjugate bases of strong acids Cl39 N0339 ClO39 139 Br39 Thus NH4C1 is NH4 NaOH is just OH39 KCOOH is just COOH39 2 Identify strong acids and bases Strong acids are HCl HNO3 HZSO4 HClO4 HBr Hl Strong bases are NaOH KOH MgOH2 BaOH2 and other alkali metal or earth hydroxides Notice what happens when you get rid of spectator ions for strong acids and bases HCl become H HN03 becomes H NaOH becomes OH39 MgOH2 becomes ZOH39 In other words all strong acids are H All strong bases are OH39 3 Identify weak acids and weak bases Hint this done by looking for the words weak acid or weak base it is also done by looking for a small Ka or small Kbvalues numbers like 14 x 10395 or 63 x 109 it is also done by looking for the word acid in a compound that is not strong acid it is also done by looking for the suffix ate Thus formic acid is a weak acid and sodium malonate is a weak base And how do you represent a weak acid HA instead of HCH3CH2COO which only serves to confuse you And how do you represent a weak base A39 instead of NaCH3CH2COO which only serves to confuse you By the time you are through with step 3 you will have identi ed the presence of all acids and bases You should have only six possible symbols representing them H or OH for strong acids and bases HA or BH for weak acids B or A39 for weak bases Any other terminology is a waste oftime on a test without much time 4 If possible N EUTRALIZE You neutralize if 0 you have both an acid and a base present 0 one or both of the acid or base are strong for example 0 HCl and Sodium Acetate are H and A39 so neutralize o Acetic acid and NaOH are HA and OH39 so neutralize o HCl and NaOH are PF and OH39 so neutralize o Acetic acid and sodium acetate are HA and A39 so do not neutralize 5 To neutralize you convert both acid and base into moles Then create a neutralization reaction into which you place the initial mole amounts Identify the limiting reagent and then calculate the nal mole amounts Convert back to molarity by dividing by total volume if necessary Examples 5 moles H and 5 moles A39 gt 5 moles of HA plus 0 moles of H and A39 1 moles of H and 2 mole of A39 gt 1 mole of HA with one mole of A39 left over 003 moles of OH39 and 001 moles of HA gt 001 moles A39 with 002 moles OH39 left over Note that after neutralization you can still have a weak base problem a weak acid problem a buffer a strong acid problem or a strong base problem In other words you have to do a neutralization to find out what kind of problem you have 6 Decide on your calculation terrain Do you work with acids calculate with pH H and Ka Want to work with bases Calculate with pOH OH39 and Kb It doesn39t matter what you choose but remember to give the answer they ask for H OH39 pH or pOH How do you move between acid and base terrain Use to move from a Ka to a Kb KW KaKb 103914 or pKW pKa pr 14 to move from a pH to a pOH KW H OH39 103914 or pKW pH pOH 14 Examples of AcidBase Problems Using Different Starting Materials in calculations use Ka for acetic acid 18 x 10395 and Kb for ammonia 18 x 10395 use Examples that use the strong acid equation Examples that use the strong base equation Examples that use the weak acid equation 01 strong or Examples that use the weak base equation or strong or 7 Examples that use the acid buffer equation Examples that use the basic buffer equation B and OH39 B and OH39 Thoughts on Thermodynamics In organizing your study plans for thermo it is essential to be able to distinguish these seemingly endless stream of very similar concepts from each other This is best done by creating a hierarchy of important facts about thermodynamics7note that the relative importance of this material doesn t run from front to back it is more like from back to front Thus we start with AG 1 AG The most important thing about themodynmics Thermodynamics tells you whether a reaction is spontaneous or not whether it occurs or not To do this we look at the Gibb s Free Energy AG and ask the following If AG positive the reaction is not spontaneous7it doesn t happen If AG negative the reaction is spontaneous7it happens So what is AG It is the free energy of a system It is a combination of three kinds of energy 0 heat energy q used to calculate the enthalpy A H 0 work usually a change in P or V PAV for a reaction involving gases 0 TAS the entropy which is a measure of the disorder in a system We can combine these three forms of energy in a couple of ways 0 AG AH 7 TAS which is a really famous equation used to calculate free energy 0 AE q w AH 7 PAV which describes all the kinds of internal energy in a system Enthalpy AH The heat of reaction Very simply this term provides a quantitative measure of how much heat is given off in a reaction 0 Endothermic reaction AH is The reaction is endothermic The surroundings get colder 0 Exothermic Reaction AH is The reaction is exothermic The surroundings get hotter Calculating AH There are two ways to do this Experimentally calculate AH mCAT using a bomb calorimeter This is how they measure the calories of food products Hess Law Hess Law Hm0 Z AHf0 products 7 Z AHf0 reactants Because of the rst Law of Thermodynamics we know that energy is conserved So if we want to calculate the AH for a reaction we can put together any combination of reactions that cancel out to leave the AH0m we want There are two ways we use Hess Law heats of formation and bond energy 0 Heat of formation AHf values in Appendix K AHf is the heat of reaction when elements in their standard state react to make an product 0 Bond Energy Rather than use Appendix K we can apply Hess Law using average values for each and every broken and formed bond from Tables on p158 and 1510 of the notes


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