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Principles of Chem II

by: Vesta Rippin

Principles of Chem II CHEM 1212

Vesta Rippin
GPA 3.98

Ronald Fietkau

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Ronald Fietkau
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This 37 page Class Notes was uploaded by Vesta Rippin on Monday October 12, 2015. The Class Notes belongs to CHEM 1212 at Georgia College & State University taught by Ronald Fietkau in Fall. Since its upload, it has received 17 views. For similar materials see /class/221955/chem-1212-georgia-college-state-university in Chemistry at Georgia College & State University.

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Date Created: 10/12/15
CHEM 1212 Principles of Chemistry 11 Chapter 17 Electrochemistry O electrochemistry is best de ned as the study of the interchange of chemical and electrical energy 171 Galvanic Cells 0 an oxidationreduction redox reaction involves a transfer of electrons from the reducing agent to the oxidizing agent 0 oxidation involves the loss of electrons reduction involves a gain of electrons 0 see Figure 171 0 see Figure 172 0 see Figure 173 0 a galvanic cell uses a spontaneous redox reaction to produce a current that can be used to do work 0 oxidation occurs at the anode negative electrode reduction occurs at the cathode positive electrode Cell Potential 0 the driving force on the electrons is called the cell potential or the electromotive force emf of the cell 0 the unit 0 electrical potential is the volt V which is defined as 1 joule of work per coulomb of charge transferred 172 Standard Reduction Potential 0 the reaction in a galvanic cell is always an oxidationreduction reaction that can be broken down into two halfreactions 0 it would be convenient to assign a potential to each halfreaction so that when we construct a cell from a given pair of half reactions we can obtain the cell potential by summing the half cell potentials 0 see Figure 175 0 the standard hydrogen electrode s potential is arbitrarily set to zero volts 0 see Table 171 Line Notation O in this notation the anode components are listed on the left and the cathode components are listed on the right separated by double vertical Lines indicating the salt bridge or porous disk RFGCSU Page 1 of 7 Ch 17 Zumdah17th Edwpd O the phase difference is indicated by the single vertical line Complete Description of a Galvanic Cell 0 a cell will always run spontaneously in the direction that produces a positive cell potential 173 Cell Potential Electrical Work and Free Energy 0 for standard conditions A G nFE where n is the number of electrons transferred F is a faraday 98485 Cmol of electrons and E is the emf for a cell 174 Dependence of Cell Potential on Concentration 0 so far have described cells under standard conditions now consider the dependence of the cell potential on concentration Concentration Cells 0 see Figure 179 0 a cell in which both compartments have the same components but at different concentrations is called a concentration cell The Nernst Equation 0 using the Nemst equation can calculate the potential of a cell in which some or all of the components are not in their standard states 0 the potential calculated from the Nernst equation is the maximum potential before any current ow has occurred as the cell discharges and current ows from the anode to cathode the concentration will change and as a result Ecell will change in fact the cell will spontaneously discharge until it reaches equilibrium at which point Q K equilibrium constant and the cell potential is zero a dead battery IonS elective Electrodes 0 because the cell potential is sensitive to the concentrations of the reactants and products involved in the cell reaction measured potentials can be used to determine the concentration of an ion 0 a pH meter is a familiar example of an instrument that measures concentration using an observed potential 0 the pH meter has three main components a standard electrode of known potential a special glass electrode that changes potential depending on the concentration of H ions in the solution into which it is dipped and a potentiometer that measures the potential between the two electrodes 0 see Figure 1712 RFGCSU Page 2 of 7 Ch 17 Zumdah17th Edwpd 0 see Table 172 Calculation of Equilibrium Constants for Redox Reactions 0 the quantitative relationship between E and A G allows calculation of equilibrium constants for redox reactions 0 for a cell at equilibrium Ecell 0 and Q K then log K n E 00592 175 Batteries 0 a battery is a galvanic cell or a group of galvanic cells connected in series Lead Storage Battery 0 lead storage battery have been used in automobiles since around 1915 with the introduction of selfstarter O in this battery lead serves as the anode and lead coated with lead dioxide serves as the cathode both electrodes dip into an electrolyte solution of sul lric acid 0 the electrode reactions are anode reaction Pb HSOA39 e PbSOA H 2e cathode reaction PbO2 HSOA 3H 2e PbSOA 2H20 cell reaction Pbs Pb02s 2Haq 2HSOaq a 2PbSOAs 2H20 O the typical automobile lead storage battery has six cells connected in series 0 see Figure 1713 0 note as the battery discharges sul lric acid is consumed the density of the electrolyte solution decreases from an initial value of 128 gcm3 an alternator driven be the car s engine recharges the battery 0 traditional storage batteries require periodic topping off because the water in the electrolyte solution is depleted by the electrolysis that accompanies the charging process 0 recent types of batteries have electrodes made of an alloy of calcium and lead that inhibits the electrolysis of water these batteries can be sealed since they do not require the addition of water 0 a car battery will last from 35 years physical damage from road shock and chemical side reaction eventually cause it to fail Other Batteries 0 the common dry cell battery was invented more than 100 years ago by George Leclanch 1 839 1 882 O in its acid version the dry cell battery contains a zinc inner case that acts as the anode and a carbon rod in contact with a most paste of solid MnOz solid NHACl and carbon that acts as RFGCSU Page 3 of 7 Ch 17 Zumdah17th Edwpd the cathode the cell produces a potential of about 15 V 0 see Figure 1714 0 in the alkaline version of the dry cell battery the solid NHACl is replaced with KOH or NaOH 0 the alkaline dry cell lasts longer mainly because the zinc anode corrodes less rapidly under basic conditions than under acidic conditions 0 the silver cell has a Zn anode and a cathode that employs AgzO as the oxidizing agent in a basic environment 0 mercury cells often used in calculators have a Zn anode and a cathode involving HgO as the oxidizing agent in a basic medium 0 an important type of battery is the nickelcadmium battery as in the lead storage battery the products adhere to the electrodes therefore a nickelcadmium battery can be recharged an inde nite number of times Fuel Cells 0 a iel cell is a galvanic cell for which the reactants are continuously supplied 0 the US space program has supported extensive research to develop iel cells the Apollo missions used a iel cell based on the reaction of hydrogen and oxygen to form water 2Hzltggt Org MM 0 see Figure 1716 0 the half reactions are anode reaction 2H2 40H gt 4H20 4e cathode reaction 4e 02 2H20 gt 40H a cell of this type weighing about 500 pounds has been designed for space vehicles 176 Corrosion O corrosion can be viewed as the process of returning metals to their natural state the ores from which they were originally obtained 0 corrosion involves oxidation of the metal since there is a loss in structural integrity and attractiveness there is a great economic impact 0 approximately one fth of the iron and steel produced annually is used to replace rusted metal 0 except for gold commonly used metals have standard reduction potential less positive than that of oxygen gas thus the oxidation of most metals by oxygen is spontaneous says nothing about the rate 0 most metals develop a thin oxide which greatly inhibits further corrosion example is aluminum 0 iron also can form a protective oxide coating however when steel is exposed to oxygen in RFGCSU Page 4 of 7 Ch 17 Zumdah17th Edwpd moist are the oxide that forms tends to scale off and expose new metal surface to corrosion 0 copper forms an external layer of greenish copper carbonate called patina 0 silver tarnish is silver sul de which in thin layers gives the silver surface a richer appearance Corrosion of Iron 0 see Figure 1717 0 because of the migration of ions and electrons rust often forms at sites that are remote from those where the iron dissolved to form pits in the steel 0 the degree of hydration of the iron oxide affects the color of the rust which may vary from black to yellow to the familiar reddish brown 0 moisture must be present to act as a kind of salt bridge between anodic and cathodic regions 0 steel does not rust in dry air 0 salt accelerates rusting increases the conductivity of the aqueous solution formed there and thus accelerates the electrochemical corrosion process 0 chloride ions also form very stable complex ions with Fe and this factor tends to encourage the dissolving of the iron again accelerating the corrosion Prevention of Corrosion O prevention of corrosion is an important way of conserving our natural resources of energy and metals 0 primary means of protection is application of a coating commonly painting or metal plating O chromium and tin used for plating form durable effective oxide layer 0 zinc used in process called galvanization zinc does not form oxide layer rather zinc is oxidized before steel sacrificial coating on steel 0 alloying used stainless steel contains chromium and nickel both form oxide layers 0 also have cathodic protection magnesium bar attached to steel pipe or titanium bar attached to hull of ship 0 see Figure 1718 0 see Figure 1719 RFGCSU Page 5 of 7 Ch 17 Zumdah17th Edwpd 177 Electrolysis recall a galvanic cell is spontaneous O in an electrolytic cell electrical energy is used to produce a chemical change 0 the process of electrolysis involves forcing a current through a cell to produce a chemical change for which the cell potential is negative 0 electrolysis has great practical importance examples charging a battery producing aluminum metal and chrome plating RFGCSU Page 6 of 7 Ch 17 Zumdahl 7th Edwpd Zumdahl Chemistry 7e Ch a me I39 Ten Liquids and Snln is Introduction recaii intramaiecuiar Wilhinlhe maiecuie banding sharing eiectmns thefarcesthatcausetheaggregatianahhecomponents afa substancemfarm a mm or saiid are intermaiecuiar forces note that the densities afa saiid and iiquid same substance are simiar whereas the new of the gas is ch mm iess Figure 101 The Schematic Representations of the Three States of Matter Table 101 Densities ofthe Three States of Water mm 101 nannies of m Three scam nf water nensily Slat gmlil lmlm umex l lllml 39 llmll 1mm 31er lll 39 101 Intermolecular Forces Forces between lralherlhan wilhinl ules molec a Dipolesdipole forces nHydrogen Bonding 7 special case ofdipoler dipole aumction monaon dispersion forces DipoleDipole Forces dipolerdipole attraction moleculeswilh quotends ofthe dipoles are close to each other elare typl39cally on co ly about 1 as strong as Valent or l39orll39c bonds l39e they are weak C Figure 102 ab lal The Electrostatic K Interaction of 3 E E o 20 M E The Intemction I o m E n lt P u 1 3 in aCondensed N State tenth DipoleDipole Forces hydrogen bonds dipolerdipole atlmclion in which hydrogen is bound to a h39gh y electronegalive atom 1F 0 Nl 439 l 39 lt ll only ahonr l we alt errong alt royalenr or l39nm39c bonds Two reasons The great pularlty orthe bond and The close approach orthe dlpules allowed by the very small slze or the hydrogen atorh Figure 103 ab a The Polar Water Molecule b Hydrogen BondingAmong Water Molecules Figure 104 The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A 5A 6A Effect on Physical Properties thelightestmemberoleahgrouplN0Flhasan unexpectedly high bulllngpulnl duElD es ecially large hydrdgeh bundlnglnlera lonslhalExlSlamong he mallesl leEELAlES with most polar XrH hdhds duElD 7 UlrelativelvlargeElenmnigatlvllvwluesoftha lightest elemamslneathgmuv whlth leadstn esverlallVDDlEVX39H bands farthe lose anarh nfthe dipoles a large ammml diehergy must he supplied D DVErEDmE these interactions hencelhe higher hdilihg paints London Dispersion Forces g relatively wean 39 gas atoms and nonpolar molecules Ar CBHIB caused by instantaneous dipole in which the ease with which electron cloud of an atom can be distorted is called polarizability Flgure105 lal An lnstantan qu tl Y n ll Polarlzatl39oncan on A A M Nonpolar I Moleculessuch l l a ls l l l Develop J l lnstantaneous 39 ahd lnduced f r quot e e Dl39poles t l y l Table 102 The Freezing Points ofthe Group SA Elements mm 102 Tll neezing Paints nf ll Gmup an Elements Element Fleming Pullll PC Hulillm Neon Argon Kryplull Xenon Fritz Wolfgang London Theoretical Physicist Lundunwzsbumtu wealthy uppeh mlddle class Germznrlewlsh fzmlly he sludled lh anhh Frankfurtlem enttlhgeh Muhlch and Parlsznd earned 2 ducturatetu 1921 lh Muhlch afterHltler sNztlunzlSuclzl rty passedt e 193 r zl laws n enhl hls ltl the UNVE Slty uf Berlln b Mmhmgm Hetuukvlsltlng pusltluns lh England and swam France and eventually emlgrated tn the new Wmdnw Puhnd Unlted Stateslrl 1939 lh 1945 he a ansuwst became 2 naturallzed CltlZErl anlum NC 102 The Liquid State as compared to gases liquids have iow compressibiiity 39ty and high density iack ofrig water is he most important Ii uid easiiy the most imporiant environmeniai issue Some Properties of a Liquid Suiface Tension The resistance to an increase in its surface area lnolai molerlllesi aplllaly Anion Spontaneous rising ofa liquid in a narrow u e Vismsily Resistance to flow imiilecules wiili Ialge inlevmoletulal fortesi Beads of Water on a Waxed Car Finish Figure 105 A Molecule inlne lnleriorofa Liquid is Attracted bylne Molecules Surrounding ll Smilin o 3 0000 so ago 00000 9009000 000 Goo 00 o the resistante of eliqiiidco increase it surface area is calledthe surface Ensmn omne liquid liquid with large mterm lecular 25 have high surface ensmns Capillary Action polar liquids exhibit capillary action the s taneous rising of a liquid in a narrow tube two different types of forces at work 1 Coheslve forces the lnlermolecularforces a nglhemoleculesoflheliquidand 2 adhesive forces the forces between the liquid molecules and their container Figure 107 Nonpolar Liquid Polar Water Forms a Concave Meniscus Viscosity a measure of liquids resistance to flow liquids with large intermolecular forces tend to be highly viscous eg oil molasses linuu39vm Structural Models for Liquids I a typical liquid might best be viewed as containinga large number of regions where the arrangements of the components are similar to those found in the solid but with more disorder and a smaller number of regions where holes are present I the situation is highly dynamic with re id fluctuations occurring in both types of regions WNW chihim is 103 Types of Solids Two types Crystalline Solids highly regular arrangement of their components table salt NaCl pyrite FeSZ Amorphous solids considerable disorder in their structures glass amp Ch w 1 1 74 Representation of Components in a Crystalline Solid Lattice A 3 dimensional system of points designating the centers of components atoms ions or molecules that make up the substance lanuuy Cl emlm Representation of Components in a Crystalline Solid Unit Cell The smallest repeating unit of the lattice simple cubic bodycentered cubic facecentered cubic januaryli 11mm Three Cubic Unit Cells Januarync charm Xray Analysis of Solids the structures ofcrystalline solids are most commonly determined by xsray diffraction d ction occurs when beams oflight are scattered from a regular array ofpoints in which the spacings between the components are comparable with the wavelength ofthe light diffraction is due to constructive interference when the waves ofparallel beams are in phase and to destructive interference when the waves are out of phase Figure 1010 a amp b Xrays Scattered from Two Ar m m K nine lnterference or Cancel Destructive lnterference One Another Figure 1011 Reflection of Xrays of Wavelength from a Pair of Atoms in Two Different Layers of Crystal unrmutm Bragg Equation Used for analysis of crystal structures r11 2 sin e distance between atoms n an integer A wavelength of the xrays Chan 121 n Types of Crystalline Solids Ionic Solid contains ions at the points of the lattice that describe the structure of the solid NaCl Molecular Solid discrete covalently bonded molecules at each of its lattice points sucrose ice imuAyKW Chran lY Type of Crystalline Solids Atomic solids subgroups metallic solids Au Ag Cu etc network solids diamond ie C Group SA solids noble gas solids Table 103 Classification of Solids Figure 1012 a An Atomic Solid b An ionic Solid c A Molecular Solid 104 Structure and Bonding in Metals metals are characterized by their high thermal conductivity electrical conductivity malleability ductility ster M best use available space This is called closest neghb Packing in Metals odel Packing uniform hard spheres to packing Each atom has 12 nearest ors hexagonal closest packed l aba l cubic closest packed l abc l Figure 1013 The Closest Packing Arrangement of Uniform Sphere we Figure 1014 Hexagonal Closest Packed Structure Figure 1015 Cubic Closest Packed Structure Figure 1016 The Indicated Sphere has 12 Nearest Neighbors Structure in Metals r u it packed Suhdsr39 magnesium and zinc are hengunzi ciusesl packed sume metaiszssume struduresthzt are nut ciusest packed fur Exampie the zikzh metzis have structureschzrzcterized by 2 bumentered cubic bcc umt ceH spherethe spherestuuch nearest neighburszscumpzred with 12 inthe ciusesl packed structures why 2 metzi adaptsthe structure it dues isnotwell undermod Bonding Models for Metals Electron Sea Model A regular array of metals in a sea of electrons Electrons are mobile and the metal ion can be easily moved around as the metal is hammered into a sheet or pulled into a wire Figure 1018 The Electron Sea Modelfor Metals Postulates a RegularArray of Cations in a SeaH of Valence Electrons Bonding Models for Metals Band lMulecular Orbllal Mcdel around metal crystal m mestcrmed rum yalence aloml orbllals utmetal atcms When an electrlc patentlal l5 placed across a Slrlp ctmetal tar currenttc low electrtms muslbelree to moVE39 the band 0 er are exclted lnlo empty onesllhe conducllon electrtms aretree tctrayel lhroughoullhe metal crystal as dlclaled by the patentlal lmpcsed onlhe metal The mulecular orbllals cccupled by these conducllng e ectrtms are called conducllon bands me m Figure 1019 olecular Orbital Energy Levels mm g ll 5 Figure 1020 A Representation ofthe Energy Levels Bands in a Magnesium Crystal Metal Alloys Substances that have a mixture ofelements and as metallic properties 1 Suhsmmional Alloy some metal atoms repletel by others ofsimilar size brass CuZn Metal Alloys continued 2 IlllelslillalAIIDV Iiiteistiteslliolesiin closest pac e metal structure are occupied by smallatoms steel iron carbon 3 Both lypea Alloy steels contain a mix ubstilutional icarboni and interstitial lCr Moi alloys gmer Figure 1021 J Two Types of Alloys Lilmull 105 Carbon and Silicon Network Solids Composed of strong directional covalent bonds that are best viewed as a giant moleculequot I brittle do not conduct heat or electricity carbon siliconrbase graphite diamond ceramics glass Figure 1022 The Structures of Diamond and Graphite Graphite and Diamond Two Forms of rbon Figure 1023 Partial Representation ofthe Molecular Orbital Energies in a Diamond and b a Typical Metal 395an Mm Emll y Mm num M0 ma MU Figure 1024 a amp b The p Orbitals a Perpendicular to the Plane of the Carbon Ring System in Gmphite can Combine to Form b an Extensive pi Bonding Network Figure 1026 The Structure of Quartz Empirical Formula SiOZ Figure 1028 a amp b Twordimensional Representations of la a Quartz Crystal and b a Quartz Glass Table 105 Compositions of Some Common Types of Glass Ceramics ceramics are typicallymaderrom clays which contain silicates and hardened by ring at high temperatures ceramics are nonmetallic materials that are strong brittle and resistant to heat and attack by micals gla is a homogeneous non crystalline frozen solution and a ceramic is heterogeneous containingtwo phases minute crystals of silicates that are suspended in a glassy cement Semiconductors A substance in which some electrons can cross the band gap the gap between lled and empty molecular orbitals is intermediate between those of diamond and met 9 Conductivity is enhanced by doping with group 33 or group 53 elements Figure 1029 a s st a ti ampbaA fquot Silicon Crystal N Doped with Arsenic b A Silicon Crystal Doped with Boron irii iiitrtstiiiiuiiamiiii 106 Molecular Solids these solids contain oiscreet molecular units at each lattice position n immi rim forms or sulrurthat contain 53 and certain forms or hosphorus that contain P4 these substances are characterized by strong weak forces between molecules 107 Ionic Solids by the strong electrostatic torces that Exist between oppositely charged ions typicallythe larger ions usually the anions are packed in one otthe loseslpacklng arrangements lhcp or cup anothe srnaller cations ht into holes among the close packed anions the packing is done in a waythat rnaxnnizes the electrostatic Table 107 Types and Properties of Solids padquot 108 Vapor Pressure and the Changes of State the process bywhich molecules of a liquid escape the liquids surface to form a gas is c Iled vaporization or evaporation vaporization is endothermi the energy to vaporize 1 mole ofa liquid at a pressure of 1 atm is called the heat of vaporization orthe enthalpy of vaporization and is symbolized byA V3 Vapor Pressure isthe pressure of the vapor present at equilibr39um is determined principally bythe size of the intermolecularforces in the liquid increases significantly with temperature Volatile liquids have high vapor pressures Figure 1038 ab Behavior of a Liquid in a Closed Container Figure 1039 The Rates of Condensation and Evapomtion OverTime for 3 Liquid Sealed in a Closed Container Figure 1041 The Number of Molecules in a Liquid with a Given Energy versus Kinetic Energy at Two Temperatures Table 108 The Vapor Pressure of Wateras a Function of Temperature mat nu ma vapnr manure In Water is a mania a ram mm r 390 9 Hum nu mu m u o 2 In 0 IT 15 5 n 1 75 mu 1 at am 5512 mo ou mu w 7 r us x Figure 1042 a amp b The Vapor Pressure of Water Ethanol and Diethyl Ether as a Function of Temperature lbl Plots of Ianvzpl versus 1T for Water Ethanol and Diethyl Ether Changes of State when a solld melts ls called the heat offusl39orl or m c rately the enthalpy of fusl39orl AH the normal meltl39rlg polnt ls de ned as the temperature atwhlch the solld and ll39qul39d states have the same Vapor pressure under con ltlonswhere the total pressure l39s 1 atmosphere 7 the normal bulllng polnt or a llquld lsthetemperature at whlchthe vzpur pressure ufthe llquld ls Exzdly 1 pher atnas can have supercoolng and superheatlng Figure 1044 The Heating Curve lNot Drawn to Scalel for a Given Quantity of Water Where Energy is Added at a Constant Rate Table 109 Melting Points and Enthalpies of Fusion for Several Representative Solids mm ins Malling minis anu quotthinks nl ruslan or 5mm chvmnlnlivc Snlids EM le nr Fuxlrm lidmull Me lng l39nlM Eamllnulld m Melting Point Molecules break loose from lattice points and solid changes to liquid lTemperalure is constant as melting occursl vapor pressure oi solitl lapul pressliie ol liquitl Boiling Point Constant temperature when added energy is used to vaporize the liquid vallol pressure of liquirl pressure r rrrroruulrrrg almosphele 109 Phase Diagram Represents phases asa function oflemperalure and pressure critical temperature temperature above which the vapor can not be lique ed the critical temperature critical point criricar lfor water Tc 374 C and 218 atml Figure 1049 The Phase Diagram for Water 39l l r r i r n nu rrrr m rant r Figure 1050 Diagrams of Various Healing Experiments on Samples of Water in a Closed Figure 1051 The Phase Diagramfor Water e mum 1m 7 ulqmlnnuN1g Table 1010 Boiling Point of Water at arious Locations um um aamm rum arwmr u vmnus lnmlnns nmllnn 1quot n m mm m mm M mm r m um a Bailing pm St um um m 7n w x5 x9 5H u w w um um Figure 1052 The Phase Diagram for Carbon Dioxide CHEM 1212 Principles of Chemistry II Chapter 15 Applications of Aqueous Equilibria 151 Solutions of Acids or Bases Containing a Common Ion O in this section we discuss solutions that contain not only the weak acid HA but also its salt NaA 0 consider a solution containing the weak acid HF Ka 72 X 10 and its salt sodium uoride NaF the reactions are HFaq ltgt Haq F aq and NaFs gt Naaq F aq O the common ion is the uoride ion when uoride is added to a solution containing HF the equilibrium is shifted to the left 0 this is known as the common ion effect 152 Buffered Solutions 0 the most important application of acidbase solution containing a common ion is for buffering O a buffered solution is on that resists a change in its pH when either hydroxide ions or protons are added blood is buffered O a buffered solution may contain a weak acid and its salt or a weak base and its salt 0 by choosing the appropriate components a solution can be buffered at Virtually any pH Buffering How Does It Work HAaq ltgt Haq A aq 0 rst case what happens when a strong base is added HAaq OH aq gt H20aq A aq 0 since A aq is already present in the original solution in a much high amount than that of the base added the change in the HAA39 will be small RFGCSU Page 1 of 3 Ch 15 Zumdah17th Edwpd 0 second case What happens when a strong acid is added Alaq HWQ gt HAWD 0 since HAaq is already present in the original solution in a much high amount than that of the base added the change in the HAA39 will be small thus the H and the pH remain essentially constant 0 an important equation when dealing with buffers is the HendersonHasselbach equation pH pKa log A HA or pH pKa log base acid 153 Buffer Capacity 0 the buffering capacity of a buffered solution represents the amounts of protons or hydroxide ions the buffer can absorb Without a signi cant change in pH 0 the capacity of a buffer is determined by the HA and A O the ratio A HA should be close to 1 for most ef cient buffer 0 this means that the pKa of the weak acid to be used in the buffer should be as close as possible to the desired pH 154 Titrations and pH Curves read over 155 Indicators read over 156 Solubility Equilibria and the Solubility Product 0 solubility is important 0 sugar and salt dissolve in water used to avor foods 0 fact that calcium sulphate is less soluble in hot water than cold water causes it to coat tubes in boilers reducing thermal ef ciency 0 consider Can at rst CaF2s gt Ca2aq F aq O as dissolution proceeds build up of Ca2 and F39 then have CaF2s gt Ca2aq F aq O ultimately have a dynamic equilibrium CaF2s ltgt Ca2aq F aq O at this point no more solid dissolves the solution is said to be saturated Ksp Ca2 F 2 O KSp is termed the solubility product for the equilibrium expression RFGCSU Page 2 of 3 Ch 15 Zumdah17th Edwpd 0 now calculate the solubility of an ionic solid from the KSp value Relative S olubilities O a salt s KSp value gives information about its solubility however must be careful in using KSp values to predict the relative solubilities of a group of salts two possible cases 0 1 the salts being compared produce the same number of ions consider CaSOA KSp 61 x 10395 gt Culs KSp 50 x 103912 gt Agls KSp 15 x 103916 O 2 the salts being compared produce different numbers of ions Bizsg Agls KSp 11 x 103973 gt Agzss KSp 16 x 1049gt CuSs KSp 85 x 1045 0 see Table 155 Common Ion Effect 0 equilibrium shifts to the left is there is a common ion present pH and Solubility 0 general rule is that if A is an effective base there will be an increase in solubility in acid example solubility of MgOH2 O A may be a weak base or a strong base conjugate or a moderately weak or a very weak acid 0 if A is not a base is a conjugate of a strong acid then pH will have no effect on the solubility 157 Precipitation and Qualitative Analysis 0 will a precipitate form when two solutions are mixed 0 first you must recognize what the potential precipitate is most of the example and problems in the text actually tell you 0 use ion product Q de ned in the same way as the reaction quotient Q and compare it to KSp if Q gt Ksp ppt forms if Q lt KSP no ppt 158 Equilibria Involving Complex Ions omit RFGCSU Page 3 of 3 Ch 15 Zumdah17th Edwpd


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