Fundamentals of Chemistry
Fundamentals of Chemistry CHEM 116
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Chem 116 Solutions Chemistry 116 Dr M RichardsBabb Dr Babb Tasks for first week of class Read syllabus Purchase lab goggles lab apron and Chem 116 Lab Manual 39om VWU Bookstore or Book Exchange NOTE l 1 Complete as lab homework Appendices A and B in the Chem 116 Lab Manual This homework is due at the beginning ofyour rst lab Wed Aug 27 Check out Dr Babb s Chem 116 website at httpwwwaswvuedumbabb This site contains handouts back tests grades answer keys lecture notes etc Register for the online homework at httpledugenwileycomledugenlclasscls68569 for 116001 1 PM lecture httpledugenwileycomledugenlclasscls68567 for 116003 830 AM lecture Begin the rst Graded Online Homework assignments 116Review etc which are due Aug 26 at 11 PMlate Tuesday night Begin working OtherHomework as speci ed on the Homework Sheet Attend one of the optional reviews on Wed Aug 20 in process of scheduling Hopefully at 830 930 or 1030 AM Hopefully at 1230 130 or 230 PM Chem 116 Solutions Chapter 14 V4 amp 12 v5 Solutions Mixtures Mixture 7 combination of two or more substances 7 no chemical reaction occurs upon mixing 7can be heterogeneous or homogeneous Homogeneous mixture 7 uniform mixture 7 compositionproperties are same throughout the sample 7 Types suspensions colloids and solutions Homogeneous Mixtures Suspension 7 7 Ex blood paint Colloid 7 7 Ex milk fog mayonaisse butter cream smoke smog Chem 116 Solutions Solution EX seawater tea coffee Types of Solutions Solute Solvent Appearance of Example Solution 02 in air Liquid in Gas Gas CO2 in water soda Liquid in Liquid Liquid salt in water seawater Liquid in Solid Solid metal alloys 6 g brass ZnCu 14 kt Gold AuAg Solid in Gas Gas Solubility Solvent water is the most common in general chemistry Solute What types of solutes will dissolve in water Answer General Rule of Thumb Portion of a crystal of a polar solute Chem 116 Solutions Example Which of the following would be more soluble in hexane CGHM than in water CBH13 CHsOH CaBr2 Wax CZOH42 NH3 HCI 06H6 HCZH3O2 Solution CompositionConcentration Solute minor component Solvent major component Solution resulting mixture of solute and solvent There are many di erent solution concentration units which all provide same basic information WewilldiscussA Molarity B Weight Percent Wt ppm ppb C Mole Fraction D Molality E Norm ality Chem 116 Solutions Molarity Molarizjz tells you how many moles of solute are present in every liter of solution solutetosolution moles of solute Molarity M Molar L solution Ex 015 M KCl implies what Is molarz39ty temperature dependent 39 0 Welght Percent Wt A 1 The weight or WW tells you how many grams of solute are present per 100 grams ofthe solution solutetosolution f l t We1ght Percent WW M X 100 mass of solution Ex 25 KZSO4 implies what 2 Related concentration Units A Parts per million ppm grams solute per 106 grams solution Ex 25 ppm Catz implies what B Parts per billion ppb grams solute per 109 grams solution Are weight percentages temperature dependent Chem 116 Solutions Mole Fraction II n t MoleFract10n X w ntotal HT 11 Solute Xmlme 5 l 501m nsolvent n 501m Solvent XSolvent nsolute nsolvent X X 1 solute solvent Are mole fractions temperature dependent Molality Molality tells you how many males afsalule are present in every kilogram afsalvenl solutetosolvent moles of solute Molahty m kg of solvent 043 mol MgSO4 EX 043 m MgSO4 1kg water ls molaity temperature dependent Chem 116 Solutions Normality Normality tells you how many equivalents of acidbase are present in every liter of solution solutetosolution Equivalent of Acid amount of acid that imished one mole ofH ions 1 eq 1 mol H Equivalent of Base amount ofbase that imishes one mole of OH39 ions 1 eq base 1 mole OH39 equivalents solute eqsolute Norm ality N vol of soln in liters L soln 045 eq CaOH2 Ex 045NCaOH2 lLsolu on What is the molarity of this solution Normality IS temperature dependent Sample Questions 1 What is the mole fraction molality and molarity of a solution made by dissolving 200 g calcium chloride in 500 g ofWater 2 A solution is 50 m NaCl What is the mole fraction of NaCl and Water in this solution 3 A glycerol C3H803Water solution is 400 glycerol and has a density of1101 gmL Calculate the molality molarity and mole fraction of glycerol in this solution Chem 1 16 Solutions 4 A 0944 M solution ofglucose c Hno6 in water has a dmsity of10624 gml at 20 c What is the molality 0mm solution 5 A sample ofhard mterhas 15 g Ca2 in every 500 mL ofwater Calculate the molan39tymola1ity and ppm ea2 in this sample Solubility of Solids in Liquid Effect anressure Pressure has NO effect an the sulublllty ufsulld salutes ln llquld sulvents Whyv Effect nfTEmpErzture Variable musdy dependent un the Sign mule AH mule alssuluuun plums Cunslder Cusogs w AHM and SrSO s wAllm 7 a on I o a a E 1 5 2 Temperature we Chem 116 Solutions Solubility of Gases in Liquids Effect of Pressure Effect of Temperature Solubility increases with increase in pressure Solubility decreases with increase in temperature Why Why 4 9 0025 2 02 0020 g 3 0015 1 O E mI VOOlO 10 7 0M mo 0005 O t C39 H 1 2 3 4 5 6 Pressure atm 40 50 20 30 Temperature 0 Pressure and the Solubility of Gases HENRY S LAW cgas kH P gas Sample Questions 1 The Henry slaw constant of methyl bromide CHsBr a gas used as a soil fumigating agent is k 0159 molLatm at 25 C What is the solubility in molL of methyl bromide in water at 25 C and a partial pressure of 125 mm Hg 00261 M 2 54 g of gaseous acetylene will dissolve in 10 L of liquid acetone at a partial pressure of 1520 torr What is the Henry s Law constant for acetylene What is the solubility of acetylene at 12 atm Chem 116 Nuclear Reactions Chapter 22 V4 and 20 V5 Nuclear Reactions Nuclear Reactions Much different than chemical reactions Not worried about electrons or charge on ion ie whether have Cu or Cu Are worried about nucleus ie which isotope is present 1H vs 2H vs 3H To balance nuclear reaction 7 Mass number balance 7 Atomic number balance 7 Is the following nuclear equation balanced Ex 238U 234Th 4He Chem 116 Nuclear Reactions IonizingNuclear Radiation or Radioactivity Stream of high energy particles or photons emitted by unstable nuclei Naturally occurring radiation from isotopes in nature 1 xiradiation 2 Bradiation 3 yradiation Synthetic radiation and other particles of importance 4 positrons 5 neutrons Chem 116 Nuclear Reactions Balancing Nuclear Reactions Examples Write and balance the following nuclear reactions 1 Fission process of 2 Ru 9 96Zr 3 1n 2 Ruthenium106 decays by emission of a beta particle 3 Aluminum25 decays by emission of a positron 4 Electron capture by polonium204 5 Nuclear transmutation of aluminum27 and deuterium with emission of an a particle 6 Fusion process of 1H 2H 9 Energy Change During Nuclear Reactions Nuclear reactions produce more energymole than chemical reactions Mass is converted to energy Einstein equation AE Amcz can be used to relate massenergy changes Nuclear Fusion Reaction Consider the fusion reaction 2H 3He 9 4He 1H 2014 3016 40026 10078 How much energy in kJ is released per mol Chemical Reaction Consider the combustion of octane main component in gasoline 2 C8H18I 25 029 9 16 0029 18 H200 AH 40942 kJ How much energy is released in kJ per mole of octane Chem 116 Nuclear Reactions Nuclear Binding Energy Energy needed to break nucleus apan into separate nucleons Example The atomic mass of deuterium is 20141 amu What is the nuclear binding energy mass neutron 100866 amu mass proton 100728 amu Radioactive Decay First Order Process Rate of decay 1 Amount Radioactive Substance Present dNdt kN Where NAmount Radioactive Isotope What is the integrated form of this first order rate law What is the halflife of radioactive decay processes Chem 116 Nuclear Reactions Examples 1 Argon41 is used to measure the rate of flow of gases from smokestacks It emits yradiation with a halflife of 110 min What percent of argon41 remains a er 1 day Cesium137 is produced in nuclear reactors If this isotope has a halflife of302 years how long will it take for this isotope to decay to 01 of its original amount Chem 116 Solubility Product Constant Chapter 19 V4 and 17 V5 Solubility and Simultaneous Equilibria Solubility Pro duct Ksp as as Small amounts of a sparingly soluble salt considered insoluble using solubility rules dissolve in water and exist in the aqueous phase as dissociated ions because the rate at Which the solid At equilibrium the ion concentrations remain the rate at Which ions crystallize to reform dissolves to give the aqueous ions the solid salt Q For Mg3AsOAZ KSp 21x1039ZEI What is the equilibrium speci ed by this KSp value The numerical value of KSp gives information about the of the salt Q What do high KSp values specify low KSp values The value of KSp depends only on Chem 116 Solubility Product Constant 2 3 Use of Solubility to Calculate KSp A saturated solution of PbClZ has PbZt 144 X 10392 M What is the solubility product constant for PbClZ A saturated solution ofCa3P04Z has Ca2 343 X 10397 M Calculate Ksp P043 and the molar solubility of calcium phosphate in water A saturated solution of AgZCrO4 prepared by dissolving solid AgZCrO4 in water had CrOf 65 X 10395 M Calculate Ksp for AgZCrO4 1 1X 1U Wm luyl Use of KSp to Calculate Solubility 39 39 gL g100 ml Molar solubility r maX number ofmoles of compound that dissolves in 1 L of solution ie to give a saturated solution 7 de ned for a saturated solution so We can use the equilibrium law to find it 39 39 L rugZinwateratzs 39 A n quot IV2117 39 39 magnesium and arsenate ions in a saturate solution of magnesium arsenate Use the values owa to calculate the molar solubility ofthe following compounds a BaCrOArmnsm b Mg OH212 m m Agsoznrxmsm Which has the greater molar solubility Agcl with Kg 1 8 x 10m or AgCrOA with Kg 1 1 x 10 macro Which has the greater solubility in grams per liter AsrCrO Chem 116 Solubility Product Constant Factors Affecting Solubility Common Ion Effect Addition ofch salt Q Consider a saturated solution ofBan KSp 18x10397 When added to the saturated barium uoride solution which ofthe following salts will affect the solubility ofBan in water NaF NaCl BaClZ KF KNOX BaNOKZ Calculate the molar solubility ofBan in pure water and in 030 M KF In which is the BaFZ most soluble pure water or 030 M KF Examples 1 Calculate the molar solubility ofl bCrO4 KSp 18x1039 in b a Pure water I mumi 10 x103 M chr0418xl 2 Calculate the molar solubility at 25 C ofMgFZ KSp 66x10399 in a 010MN3F66X1E7M b 010MMgClzozxm M Factors Affecting Solubility pH of Solution A and to base ofWEAKACID will INCREASE the solubility ofthe salt Q Explain how addition of HCl or lowering of pH affects the solubility of CaFZ Ksp 39X1039 in aqueous solution Metal hydroxides also contain the conjugate base ofa weak acid ie OH is the conjugate base ofthe weak acid H20 and will INCREASE in solubility as strong acid is added Q Explain how addition of strong acid affects the solubility of FeOH3 Ksp 16X103939 Q Which of the following compounds are more soluble in acidic solution than in pure water AgCl PblZ AlOH3 MnS HgZBrZ Zuco3 Ni0HZ 9130304Z AgOH Mg0HZ Chem 116 Solubility Product Constant Examples 1 Calculate the molar solubility and pH ofa solution saturated with Mng2 K PMgOHZ 5 o x 1042 2 Calculate the molar solubility ofMng2 in water buffered at a pH 0f8 00 Precipitation of Ionic Compounds Question Willa precipitate form if aqueous solutions of AgNO3 and KZSO4 are mixed Answer It depends on To decide if a precipitate Will form calculate the value ofthe ion product IP or Qsp 1 2 3 If 1P gt Ksp then solution is andprecipitate form IP lt Ksp then solution is 7 and precipitate form IP KSp then solution is and precipitate i 7 form Examples 1 Willa precipitate form if 100 mL ofO 075 M MgNOZ2 is mixed with 200 mL ofO 010 M NaZCOZ 2 Will 39 39 39 mL ofO 050M AW W n 39 39 39 mLofO OIOMKZSOA 3 Willa precipitate form if 100 mL ofO 0250 M Bach is mixed with 250 mL ofO 00100 M ngmoz Chem 116 Solubility Product Constant Qualitative Analysis Scheme A procedure for separating and ia enti ing metal cations present in an unknown solution Group based separation into ve groups is by differences in Ksp values and NOT by solubility rules Gr0u 1 Ex 8 Ag Hgft Pb2 Add HCl F Groupl precipitate AgCl HgZClz PbCi2 Group IIExp 9 Pb2Cu2Hg2Bi3 Group IIIExn 10 Mn2Fe3 Ni2 Al3 Group IVExn 11 Ca2 Ba2 Sr2 Gr0u VEx 12 Na K Mg2 NH4 1 2 Separation of Group I from Groups IIV Based upon di erences in Ksp values for the metal chlorides Ksp values for PbClZ AgCl and HgZClz are low Ksp values for most other metal chlorides are high A solution is 0 0015 M in each of the cations Ag Pb and ng2 What concentration of chloride ion must be used to precipitate as much of the ng2 as HgZClz as possible without precipitating the chlorides of Ag and Pb2 KspHg2C12 1 4 X 1018 KspPbC12 1 2 x 105 KspAgCl 1 8 X 1010 Consider the question above What concentration of Cl39 is needed to precipitate as much of the Ag and ng2 as possible without precipitating the Pb What is the concentration of ng2 ions in the solution at this concentration of Cl39 At this Cl39 concentration has most of the ng2 been precipitated from solution Chem 116 Solubility Product Constant More Selective Precipitation Separation of Group II acid insoluble from Group 111 base insoluble cations 39 cations M 39 r L L 39 39 39 39 39 ul de M Group 11 Metal sul des Insoluble at low pH pH lt 1 and at high pH acid insoluble sul des Group 111 Metal Sunidcs Soluble at low pH but insoluble at high pH pH gt a base insoluble sul des The equilibrium tupu a ta 39 A 39 valuesis Low pH conditions rpm gt Km only for metal sul des with low K59A values Group 11 High pH conditions rpm gt Km for metal sul des with high andlow K WA values Groups 11 and HI w or solution Sul de g A Sul de g A PbS 3x107 Mns 3x10m CuS 6X10 Fes 6x102 Hgs 2x1032 Nis 0 8 Zns 0 03 1 A solution with a pH0 52 and HIS concentration ofO 10 M is 0 0010 M in each ofthe cations Pb Hg Mn Ni and Zn2 Under these Group 11 conditions which metal cations will precipitate as the sul de A 39 39 M in each 39 39 Ifthew 0 10 M what pH is neededto precipitate all seven ofthe metal cations Chem 116 Solubility Product Constant Other Examples Precipitation and Separation 1 A solution is 0 500 M in each ofthe ions Ni2 and Cr and has a pH of4 00 Solid NaOH is added to precipitate the hydroxides K PNiOH2 2 x 1045 K PCrOHZ o 3 x 1073 a Before NaOH is added will either ion be precipitated as the hydroxide b 39 L u nuju m pn ofthe solution c 39 39 39 n p iur 39 39 39 39 Ni 2 A solution is 0 0050 M in Sn1 and Al and has a pH 1 00 Solid NaOH is added to make the solution more basic which ofthese metal cations will precipitate first 7 x Sn0H2 Kg 3 x 10717 A10H3 Kg 7 2 0 10731 3 A solution is 1 0 x 10 3 M in each ofthe metal cations cm Pb2 Hy and Ag SolidNaBr is addedto this solution In what order will the bromides precipitate CuBr K59 o 3 x 1079 AgBr K59 5 4 x 1043 PbBr2 K59 o o x 1076 ngBrz K o 4 x 10713 Formation of Metal Complex Ions or Coordination Compounds w salt Metal Complex IonDefinition Ligand Formation of a metal complex ion is an example of if chemistry Example CuCO3 is insoluble with KSp 25x10391 However addition of ammonia increases the solubility ofthis salt and causes CuCO3 to dissolve Explain Hint CuII forms the soluble ammonia complex ion c 3421ltf11x1013 Example Silver chloride KSp 18x10391 is insoluble in Water and in acid but dissolves in an excess of aqueous ammonia Explain Hint SilverI forms the soluble complex ion AgN39l3z Kf 17x107 Q Calculate the molar solubility ongBr Kg 5 4x10 at 25 c in water b 0 75 M N111 Chem 116 Solubility Product Constant Sample Questions A solution is 0 60 M in CuNHjAZ Kr 1 1 x 10 3 Calculate the concentration of ce solution NHa 1 o x 1049 KfCuNH3A 1 1 x 103 Calculate the solubility of Cu0H2 in a solution ofl 2 M Kg Cu0H2 Cu2 and NH3 in this a 1 t Ni2andnn39 1000 ml ofl 0 M NH3 KNiNH362 5 o x 108 W 39 1Kf17x1o739 39 39 10MA complex is formed the solution is make ofO 030 M in Nacl will any AgCl precipitate NiN032 are added to 3 and1 0 M NH3 A er the K PAgCl 1 8 x 10m Chem 116 Integrated Forms of Rate Laws Integrated Rate Laws Gives the mathematical equation for how reactant concentration varies with time A First Order Reaction A gt Products Where Rate kA e This IS the equation ofthe slope ofplotofA Vs t What is the integrated farm afthisfirst order rate law Integrated form of rst order rate law which is equation of straight line 2 Integrated form of rst order rate law in exponential form First Order Rate Law as a Straight Line 1nAt kt 1nA0 y mx b NOT 1st order 1st order NOT 1st order 1nA0 intercept a a lt a s s 1 s 39 39 quot r o v l c I s a 39l s quot 39 0 L k slope 39o Chem 116 Integrated Forms of Rate Laws B Second Order Reaction A A gt Products Where Rate kAZ e This IS the equation ofthe slope ofplotofA vs t B r quot39 mm mw 1 Integrated form of second order rate law which is equation of straight line C Zeroth Order Reaction A gt Products Where Rate kA0 e This IS the equation ofthe slope ofplotofA Vs t thix zeroth mm mw 1 Integrated form of zeroth order rate law which is equation of straight line Chem 116 Integrated Forms of Rate Laws Time it takes for half of the original amount of reactant to reactdisappear When one halflife has elapsed i t 0 30 O t T or t i l 12 E Each halflife is twice as lon as the A a i g 0 j preceding one because t12 1kAO and the concentration of A at the beginning I v w r e e of each successive half life is smaller by a lt i t 121j factor of2 H 2 l I quot i t 2t12 E in i 1 and g A a o 0 quotquot39 quot 39 A U 1512 t t 31512 1At 0 l M Ab4 Ab8 tm 0 t 0 2 4 6 8 1C To find the numerical expression for halflife Time arbitrary a NOT E The graph above shows how the halflife of a second order Plug the conditions above into the integrated form of the rate law Reacnon Changes With reacmm conc and rearrange for T Halflives for First Second and Zeroth Order Reactions A From the conditions given on the previous slide At A02 when t t nd the equation for the halflife of a rst order reaction For a rst order reaction how does the halflife depend on the initial concentration of reactant B From the conditions given on the previous slide At A02 when t t nd the equation for the halflife of a second order reaction For a second order reaction how does the halflife depend on the initial concentration of reactant C From the conditions given on the previous slide At A02 when t t nd the equation for the halflife of a zeroth order reaction For a zeroth order reaction how does the halflife depend on the initial concentration of reactant Chem 116 Integrated Forms of Rate Laws Summary Kinetics Integrated Rate Law Halflife First Order 1nAt kt 1nAO 1n 2 OR AiAio eh I Z T Second Order 1 At kt 1 AO 1 Alok Zeroth Order At kt AO A0 2k Sample Questions r quot 39 39dilutesodiumhquot 394 quot 394 2H202aq s 21201 025 4 inHjOZ L r 39 L 39 n at7n Ci518X10395squotand the initia1 concentration is 0 30 M a What is the halflife in hours ofthe reaction at 20 m What is the concentration oszo2 anei four halflives 39L A e the equation What will be the concentration oszo2 a er555 minutes b c d e What is the initial rate ofthe reaction 2 A reaction is first order in the concentration ofreactant This reaction has a halflife of102 seconds b If0 75 M of reactant is present initially how much reactant would remain a er 2 minutes c After three halflives what percent ofreactant will remain Chem 116 Integrated Forms of Rate Laws e A c L I Times o 50 100 150 zoo 300 400 500 I p10 800x104 658x104 559x103 485x104 429x104 348x104 293x103 253x103 I a What is the order ofthe reaction smmmmm mom b What is the value ofthe rate constahtmsm in c What is the concentration orNo2 at time t 20 o min13ximM d What is the halflife ofthe reaction when NOAH 5 00 x 10393 M a mum e What is m when NOAH 3 00 x 1039 M 52mm r How much time will it take for 25 orNo2 to react 77s Analysis of Experimental Data In N01 First Order Second Order Zero Order Chem 116 Integrated Forms of Rate Laws 4 The following data were collected for the reaction 2 HIg 4 1123 123 at580 K Time min HI 0 3 00 M 16 7 0 120 M 33 3 0 061 M 50 0 0 041 M 66 7 0 031 M a What is the rate law for this reaction b What is the numerical value ofthe speci c rate constant c What is the initial halflife for this reaction d A er how much time will only 20 ofthe original amount ofHI remain 5 A certain reaction is known to be zeroth order in reactant Under certain conditions this reaction has an initial halflife of 16 min at an initial concentration ofO 0 M How much time will it take for the concentration to drop to 0 05 M Chem 116 Colligative Properties Colllgatlve Propertles Properties that depend on the number of solute particles dissolved in solution amount and not on the identity of the solute particle Note Number of dissolved solute particles in solution depend on Whether the solute is a strong weak or nonelectrolyte l Vapor Pressure Lowering CASE 1 Nonvolatile solute dissolved in solvent Vapor Pressure VP pure solvent gtVP solution Vapor pressure gauges a b Chem 116 Colligative Properties Raoult s Law Vapor pressure afa solution is dependent on how much i e cane SOLVENT is present 0 Psoln XSGZVPSOZV PMquot vapor pressure of the solutlon X 501m mole fraction of the solvent 35771th vapor pressure of pure solvent Raoult s Law works best for ideal solutions Derive the expression for the change in Vapor Pressure 1 Calculate the vapor pressure ofa solution made by dissolving 200 g glucose C HIZO in 5000 g of Water The vapor pressure of pure Water is 471 torr at 37 C 2 What is the vapor pressure in mm Hg ofa solution made by dissolving 50 g of CaClZ in 500 g of H20 at 70 C The vapor pressure ofpure Water at 70 C is 2337 mm Hg 3 How many grams of sucrose must be added to 320 g ofwater to lower the vapor pressure by 15 mm Hg at 25 C The vapor pressure ofwater at 25 C is 238 mm Hg and the molar mass ofsucrose is 3423 gm0141x179 Chem 116 Colligative Properties respectively what is the vapor pressure of this solution 250 g acetone in 250 g ethyl acetate is 219 torr pressures of pure water and ethanol are 238 mm Hg and 612 mm Hg at 25 C 2 Acetone C3H60 and ethyl acetate C4H802 are organic liquids often used as solvents At SO C the vapor pressure of pure acetone is 285 torr What is the vapor pressure of pure ethyl acetate at 30 C if th e vapor pressure of a solution of Vapor Pressure Lowering CASE 2 Two or more volatile substances mixed Both substances contribute to VP of solution F 39 f l f t39 th P501 p p ttgfczpzi39gsestuiigizgzrme of partial vapor pressures for A and B but om Raoult s Law gigsirure of pure A eq a vapor presSU T 1900 Vapor 0 53 pressure g S ofoo of pure E Hence 3 fquot g veer e o gt 0 9 d ampq9 A 1 05 0 B o 05 1 Mole fractions of A and B Sample Questions 1 In a solution of water in ethanol the mole fraction of water is 025 lfthe vapor Chem 116 Colligative Properties Boiling Point Elevation Normal BP ofasalutmn in 39 soluteisalwa quot r pm solvent BP gt BPpure solvent s oln TBsoln gt TBO anryresm of me39pue snivent l E I w I a I E Isolu nn ATE TBSOIH TB I bailing I Inint Vapor vmssu39e of the Elm I g I I Boiling Point Elevation What is the increase in the boiling point of the solution ATb Kbxm not the new BP nlolality of solute boiling point particles elevation molal BP elevation constant that is DIFFERENT for different solvents units are Ckgmol Chem 116 Colligative Properties Freezing Point Depression Freezing point The temperature at which both the solid and liquid ofthe substance COEXIST FP lt FP soln pm 501m 0 TFsoln lt T Fsolvent V or 155me mewpug solvent 7 o ATF 7 T Fsolvent 7 TFsoln Vapor pessun at in solution Pram atn W SDI an mnpemuze lt me an pom Freezing Point Depression How much lower is the freezing point of the solution molality of solute this gives the particles CHANGE ATf Kf m not the new FP M l mozality kg solvent molal FP Depression constant that is DIFFERENT for different solvents freezing point depression units are Ckgmol And different from Kb Chem 116 Colligative Properties Sample Questions 1 What are the boiling points ofthe following aqueous solutions for water Kb 051 c kgmol 090 m sugar solution 090 m SrClOKZ 2 What is the normal boiling point in DC of a solution prepared by dissolving 150 g of aspirin acetylsalicylic acid CBHEOA in 7500 g of chloroform CHCIK The normal boiling point of chloroform is 617 C and Kb for chloroform is363 DCkgmol 3 What mass of NaCl is dissolved in 200 g ofWater ifthe freezing point ofthe solution is 214 C ngater 186 DCkgmol a 39 39 39 39 39 A 39 100 g camphor The freezing 39 17835 C eigui w in PCB For camphm Kf 377 Ckymol and Tf 17950 C 4 A 0100 5 lscaioiene is a dietary source of vitamin A Dissolving 00250 g of lscamiene in 150 g ofcamphor gives a 39 39 39 39 p o Kffor camphor is 377 Ckgmol 537 ymol 6 39 39 Kbwater 051 ac kymol 050 m sugar 050 m CaCl2 050 m NaCl 050 m HF 050 m AlCl3 040 m NaZSOA 050 m KNo3 050 m c Huo6 020 m A1cijoz3 050 m HCZHZOZ Chem 116 Colligative Properties Osmotic Pressure 7t semipermeable membrane solvent molecules can pass through solute molecules cannot pass through Osmosis Net movement of SOLVENT particles through a semipermeable membrane from a region of low concentration dilute solutionpure solvent to a J region of high concentration I 3 Solution Osmotic membrane Pure water k7 Osmotic pressure Initial conditions A solution B is separated from pure water A by an osmotic The extra pressure required to stop osmosis of the membrane no OSmOSIS has yet occurred solvent through the semipermeable membrane After a while the volume of fluid in the tube has increased visibly Osmosis has taken place A back pressure is needed to prevent osmosis e amount of back pressure is the osmotic pressure of the solution Osmotic Pressure osmotic pressure atm molarity of the solution molL This equation can also be rewritten as a form similar to the Ideal gas equation Experiments by van t Holf in 1887 showed that the osmotic pressure is related to the molarity of the solution according to the equation 2 M R T 4 Kelvin temperature Ideal GAS CONSTANT 008206 Latmmolk Chem 116 Colligative Properties Osmotic Pressure Effects A red blood cell is placed in each of the following solutions What Will happen to the red blood cell in each solution Which solution is isotonic hypotonic hypeItonic Csoin Csoin Csoin csoln gt ccell csoln lt ccell csoln ccell Sample Questions 1 What osmostic pressure in atm would you expect for each of the following solutions a 500 g ofNaCl in 3500 ml of at 50 C b 633 g of sodium acetate CHKCOZNa in 550 ml of aqueous solution at 10 oc SZatm 2 A 200 g sample ofaprotein dissolved in 0100 L of solution exhibited an osmotic pressure of 16 mm Hg at 25 C What is the molar mass ofthe protein 3 What is the molar mass of sucrose table sugar if a solution prepared by dissolving 0822 g of sucrose in 3000 ml ofwater has an osmotic pressure of 149 mm Hg at 29 K Chem 116 Colligative Properties A 00500 M FeCl3 solution exerts an osmotic pressure of416 atm at 25 C Calculate the van t Hoff factor Why is the experimental van t Hoff factor less than the theoretical van t Hoff factor A solution of494 g KzFeCN dissolved in 100 g ofwater has a freezing point of 11 W many ions result from the dissolution ofthe KzFeCN in water When stranded at sea without fresh water why is it NOT a good idea to drink seawater Use your knowledge of osmotic pressure to explain how fresh water can be obtained from seawater Chem 116 Approach to Eq and Le Chatelier s Principle Reaction Quotient QC The value of QC is used to predict the equilibrium position and the approach to equilibrium emember all reactionsproeeed spontaneously toward equilibriuml Products Reactlon Quotlent QE Q Reactanml Example At 927 CKE391 for the reaction COg 3 Hzg CH4g HZOg Initially CO HZ 00200 M and CH4 HZO 000100 M Under these initial 0 ditions is this reaction at equilibrium If not Which direction Will the reaction proceed to attain equilibrium InGeneral IfQEgtKEthen IfQEltKEthen IfQEKEthen Sample Questions 1 At1000 c1ltc 1 17 for the reaction 3025 Cs 2 303 A 10 0 L vessel contains 1 5x103 mol of co2 and 5 5x103 mol of co Some solid carbon is added andthe temperature increasedto 1000 c Will more COg form 2 Consider the reaction 2 NOBrg 2 NOg Brits Kc 3 07x10 at 24 C For each ofthe following sets of initial conditions u h in 39 39 39 39 quot39L39 A Now 0 0510 M B Now 0 115 M C Now 0 500 M NO 0151 M No 0 0159 M NO 0 0170 Brz00142M 00140M 3 A mixture ofl 57 mol osz 1 92 mol of H2 and 8 13 mol ofNH3 is introduced into a 20 0 L reaction Vessel at 500 K At this temperature the equilibrium constant for the reaction Nzhg 3 Hang NH 3 isl7x102 quot 39 quot39 39 39 39 1 39L 39 Lfnot ultimatum marmrmmurom nmurmurarcanrmmmraemrmm Chem 116 Approach to Eq and Le Chatelier s Principle Relationship between Initial concentrations and Equilibrium concentrations The Concentration arICE Table 2 IClg 1 Initial 0 M Change Initial Cone Change in Cone Equilibn39um Cone The initial concentrations of the chemicals are going to CHANGE as the reaction occurs before equilibrium is rea e The changes in the different chemicals are RELATED via the coefficients in a BALANCED chemical equationH Example Consider the equilibrium and initial conditions shown below Is this reaction at equilibrium fnot which way will the reaction proceed to attain equilibrium 25 3123 Kc o 22 M 22 M A er reaching equilibrium the concentration ofthe ClZ is 009 M What is the numerical value of Kc Sample Questions 1mm Change 1mm Change 1mm Change Equilibrium Equilibrium Equilibrium run A A c for the equilibria below Hag 175 2HIg Kc 0 M 0 M 5 000 M 0 730 M 3 Aaq 2 13an Caq 2 Daq Kc 2 6 00 M 2 00 M 1 00 M 0 M 0 50 M 2N20g 3023 mole Kc 0 020 M 0 056 M 0 M 0 010 M Chem 116 Approach to Eq and Le Chatelier s Principle Calculation of Equilibrium Concentrations from Initial Concentration and Kc Exam 12 E050 molPClS is injected into a 20 L vessel What Will be the equilibrium concentrations of all species The equilibrium equation is given below PClsg PClan Clzg Kc 18 at 250 c HINT For the general Quadratic Equation 2x2 bx g 0 2 the solution is x m 2a Sample Questions 1 The ah r N205 023 2N0g Kc 1 7 x 10393 at 2300 K Ifthe initial concentrations ofN2 and 02 at 2300 K are both 1 40 M What are the concentrations ofNO N2 and 02 when the reaction mixture reaches equilibrium 2 The equilibrium constant Kc for the reaction Hang 3025 H20g C03 is 4 2 at 1650 C Initially 0 80 mol H2 and 0 80 mol CO2 are inj ected into a 5 0 L ask Calculate the concentration ofeach species at equilibrium nu C01 ammo1p Co B u m 3 Consider the reaction at equilibrium below 2N02g N204g Eq 0 25 atm o 25 atm L mum mm Chem 116 Approach to Eq and Le Chatelier s Principle Le Chatelier s Principle If a stress is applied to a chemical system at equilibrium Qe Ke that removes the system from equilibrium QC iKC then that system will act to alleviate the stress and regain equilibrium Stresses that may remove system from Eq Stresses that do NOT remove system from Eq NOTE Reactions always proceed spontaneously toward equilibrium Effect of Addition or Removal of ReactantProduct 1 Consider the equilibrium 21Clg 12g Clzg KC 012 74 M c Which vva 39 39 39 fr 0 74 M D Which way will the reaction proceed if an ofthe c12 is removed A If 1C1 0 25 M and 12 c121 0 09 M is this reaction at equilibrium ich vva 39 39 39 39 orm 39 39 2 Consider that the reaction shown below is at equilibrium BaSOAs BaOs SOKg Hi I nhl d ivmxd 3 The reaction of ironIII oxide With carbon monoxide occurs in a blast furnace When iron ore is reduced to iron metal FeZOKs 3 COg 2 Fel 3 COZg Use Le Chatelier s principle to predict the direction of the net reaction When an equilibrium mixture is disturbed by A Adding FeZOZ B Removing co2 3 Adding Fe D Removing co Chem 116 Approach to Eq and Le Chatelier s Principle Effect of Change in Pressure Due to Change in Volume Especially important for gasphase reactions As pressure increases due to a decrease in volume the net reaction Will occur in the direction that 7 the number of moles of gas As pressure decreases due to an increase in volume the net reaction Will occur in the direction that 7 e number ofmoles ofgas uuiuer quot nicn a quot 39 uecreasin the volume A N20g N02g 3 NOg KC 14x10391 at 200 C B Pc1g 3125 PC15g c Ca0s C02g CaCOZs mu 4 ml iurcl A C05 H20g 3025 H2g B 2C0g Cs 3025 1023 0 NZ 9 Effect of Change in Temperature When temperature changes the numerical value 1ch changes We will treat temperature as heat Treat heat as either a product of reaction exothermic or reactant endothermic Endothermic reaction AH Heat Reactants Products As temperature is increased are products or reactants more favored As temperature is increased What happens to the numerical value of Kc Exothermic reaction AH Reactants Products Heat As temperature is increased are products or reactants more favored As temperature is increased What happens to the numerical value of Kc Chem 116 Approach to Eq and Le Chatelier s Principle 1 2 3 4 Sample Questions In the rst step of the Ostwald process for the synthesis of nitric acid ammonia is oxidized to nitric oxide by the reaction 4 Nng 5 02 4 NOg 6 H20 g AH 9056 k How does the equilibrium amount of NO vary With an increase in temperature Consider the reaction below Which has already attained equilibrium NZOAQg 2N0Z g AH 572 k colorless brown In Which direction Will the reaction proceed if the temperature is increased Consider that the reaction Nzg Ozg 2 NOg AH 181 k is already at equilibrium Ifthe temperature is decreased Which Way Will this reaction proceed to regain equilibrium Consider the equilibrium NZHAQg Hzg 2 NH3g AH 188 kJ In What two Ways could the production of ammonia be maximized