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Recaps and Additional Slides I will keep updating these. Please check back! Chem 20B: Reference Slides & Recaps READ THE UPDATED SYLLABUS BEFORE AND AFTER EACH CLASS http://www.nano.ucla.edu/_psw/chem20bw17.html or http://bit.ly/chem20Bw17 Syllabus will be adjusted after each lecture. Upcoming assignments are finalized when date is green and underlined. Lecture 1, Monday 9 January Textbook: Principles of Modern Chemistry, 8th ed, Oxtoby, Gillis, & Campion Discussion: Location & time for your Section on MyUCLA You will learn both scientific intuition and how to work quantitative problems. You will also learn some chemistry. Goal: be an informed citizen, have basic scientific understanding and thinking skills, and have background to go further in chemistry, science, engineering, etc. I expect a lot of you, so that we can cover key issues in science and engineering this quarter Come prepared by having read material and be ready to discuss it. Turn in homework in your section folder each lecture. You will make up a problem (15×) for a set of lectures and answer it. (The top few of the quarter receive nominal extra points + immortality!) No late homework submission without prior approval of your TA. 1 Chem 20B: Highlights from the Syllabus, cont. Grading: Homework 25% (5% submitted + 10% graded problems + 5% creative problem + 5% reading memos) Assessments 10% (5 × 2%) Midterms 40% (2 × 20% each) Final 25% Exams: No notes or calculators or phones or devices You will receive a periodic table and list of formulas and constants Recording lectures is not allowed without my explicit permission, and under no circumstances can be posted online or otherwise transmitted Office hours: Tuesday 1030-1130 AM & Thursday 230-330 PM, 3041 Young Hall (we may move if crowded) Often on iChat, AIM, WeChat as psweiss TA office hours are on the web site READ THE UPDATED SYLLABUS BEFORE AND AFTER EACH CLASS Key Chemical Knowledge How big is an atom? How strong is a chemical bond? NB- energy is a critical parameter in chemistry and especially this quarter Choose your favorite energy unit (kcal/mole, kJ/mole, J, eV, cm-1) and learn all the conversions How energetic is a visible photon? How does the rest of the electromagnetic spectrum compare? Dimensional analysis is very useful 2 Recap of Lecture #1: Intro & Gases Final exam: Tuesday 21 March 630-930 PM, rooms to be announced Simplified class web site & syllabus sites (case matters): bit.ly/chem20Bw17 & bit.ly/Ch20Bw17Syl Energy and units of energy - kcal/mole, kJ/mole, J, eV, cm-1 Bond strengths, photon energies Spectroscopies (much more to come here) Atomic size Temperature & pressure (State functions & linearizing relationships) Average speed of N2 in air ~0.5 km/sec Density change between solid N2 and N2 in air is ~600×. In general, estimate 1000× En route today to Ideal gas equation (of state) pV = nRT Dimensional analysis Recap of Lecture #2: Gases Final exam: Tuesday 21 March 630-930 PM, rooms to be announced Simplified class web site & syllabus sites (case matters): bit.ly/chem20Bw17 & bit.ly/Ch20Bw17Syl Ideal gas law pV = nRT In solving problems: Make table of initial and final (and sometimes intermediate) conditions Convert units to match & check that units cancel properly – dimensional analysis Touchstones: N2 at room temperature ~0.5 km/sec Mole of ideal gas (at STP) 22.4 L Liquids and solids are denser than gases by ~1000× 3 Recap of Lecture #3: Non-Ideal Gases Mass Spectrometry (start) Real atoms and molecules interact Know energy ranges of intramolecular and intermolecular interactions Molecular, interatomic, and intermolecular potentials Repulsive wall is steep on close approach Depth of potential well is (~) bond strength Position of potential well is bond length Mass spectrometry Use fragments and isotope ratios to identify to determine connectedness of molecules and parts of molecules Recap of Lecture #4: Phase Transitions Phases Solid – Condensed (close together), organized Has vibrational but not translational nor rotational motion Liquid – Condensed, not organized Has translational, vibrational, and rotational motion Gas – Separated (much more randomness è higher entropy than condensed phases) Has translational, vibrational, and rotational motion Plasma – high energy, ionized gas Ionization potentials are several eV (UV) Transitions Breaking bonds takes energy, SO making bonds gives off energy (heat) Ionization energies are comparable to bond energies 4 Recap of Lecture #5: Interactions Interactions and Interaction Strengths Ionic bonding Charges and separation Covalent bonding Metallic bonding Delocalized electrons Comparable cohesive energies (bond strengths) Weaker Interactions Ion-dipole Hydrogen bonding Dipole-dipole Ion – induced dipole Dipole – induced dipole Dispersion (fluctuating dipole – induced dipole) Recap of Lecture #6: Thermodynamics I ΔG = ΔH – TΔS So, ΔH < 0, making stronger bonds, is favorable So, ΔS > 0, increased disorder, is favorable ΔH and ΔS vary little with temperature. ΔG does vary with T è effect of ΔS ΔG < 0 Keq > 1 Spontaneous ΔG > 0 Keq < 1 Not spontaneous ΔG = 0 Keq = 1 System at equilibrium (with equal amts of reactants & products) Much more entropy in a gas than in a solution, liquid, or solid (in that order) Polyatomic molecular gases have more entropy than diatomic molecular gases than atomic gases 5 Recap of Lecture #7: Solutions, Acids, & Bases Solution composition Most common – molarity = moles/L Also – mole fraction, molality, mass fraction (and normality) Acid/Base Definitions Arrhenius: Acid - Proton donor, Base - Hydroxide donor Bronsted-Lowry: Acid - Proton donor, Base - Proton acceptor Lewis: Acid - Electron pair acceptor, Base - Electron pair donor Equilibria Strong acids dissociate essentially completely in water Strong acids (for our purposes): HCl, HBr, HI, H2SO4, HNO3, HClO4 Strong bases react completely to give OH¯ in water They are (for our purposes) Alkali (Group 1A) hydroxides: LiOH, NaOH, KOH, RbOH, CsOH Heavy alkaline earth (Group 2A) hydroxides: Ca(OH)2, Sr(OH)2, Ba(OH)2 H¯(typically used as NaH), NH2¯ (and there are more) Ka Kb = [H+][OH¯] = Kw = 10-14 pX = -log10X pKa + pKb = 14 = pH + pOH Recap of Lecture #8: Equilibria & Oxidation States Periodic Trends Electronegativity ì Electropositivity í Ion and atom sizes í These can be quantified, but be careful of sign conventions – use your intuition Oxidation-reduction (redox) reactions Disproportionation reactions – same element is both oxidized and reduced. With electrochemistry, we can quantitate amount of reaction Spontaneous reactions produce energy (generally make stronger bonds) Keq>1 Nonspontaneous reactions require energy, e.g., electrolytic reactions, Al reduction Assign formal oxidation states: 1. Oxygen is almost always -2 2. Halogens (F, Cl, Br, I) always are -1, except when Cl, Br, I are bound to O or F 3. Hydrogen is always +1, except when bound to group I, II, or III metals, then -1 4. Other elements to balance charge on compound (can have mixed valency) Ka Kb = [H+][OH¯] = Kw = 10-14 pKa + pKb = 14 = pH + pOH Buffer pH~pKa 6 Recap of Lecture #9: Oxyacids, Thermodynamics Oxyacids For a particular central atom, the more positive the formal oxidation state, the stronger the acid For a series of oxyacids where the central atom has the identical formal oxidation state, the more electronegative the central atom, the stronger the acid Laws of Thermodynamics 1 Energy is conserved 2 Entropy increases 3 At 0 K, S = 0 for a pure element ΔG = ΔH – TΔS So, ΔH < 0, making stronger bonds, is favorable So, ΔS > 0, increased disorder, is favorable ΔH and ΔS vary little with temperature. ΔG does vary with T è effect of ΔS Recap of Lecture #10: Thermodynamics & Electrochemistry ΔG = -nFE and for standard states: ΔG° = -nFE° n = number of electrons transferred in a balanced redox reaction F = Faraday = 96,500 coulomb/mole e− = 96,500 J/V-mole e− Standard States: Solid Pure solid Liquid Pure liquid Gas 1 atm pressure Solution 1M Temperature Usually 25 °C ΔG° = -2.303 RT log10Keq E° = 0.059 log10Keq n ΔG° = ΣΔGf°(products) - ΣΔGf°(reactants) For elements, ΔGf° = 0 7 Exam #1 Topics Midterm #1 Tuesday 7 February, 7-9 PM Exam #1 covers through today’s lecture: recaps and coverage at http://bit.ly/20B17recaps (also linked in syllabus) Define temperature, pressure, state functions, phases Bond lengths and strengths Energy scales Interactions and potentials – intramolecular, intermolecular, solids, liquids Periodic trends Ideal gas law and deviations Partial pressures and concentrations Thermodynamics, equilibria, and electrochemistry Spontaneity, enthalpy, entropy, free energy, cell potentials Phase transitions and equilibria Typical, water, CO2 Solid, liquid, gas, supercritical fluid Energy changes with making and breaking bonds, heat Acids & bases Electrochemistry Relation to thermodynamics, energy storage Heat capacity Recap of Lecture #11: Thermodynamics, Electrochemistry, and Concentrations Le Chatelier’s Principle Disturb a system from equilibrium and it will move to restore that equilibrium è One way to drive a reaction is to remove product Quantify with concentration dependence of ΔG and E. Batteries Lead acid battery Dry cell, alkaline cell Rechargeable Ni-Cd battery To get higher voltages, stack up cells in series (e.g., car battery 6 × 2 V = 12 V) Electrolysis Driving non-spontaneous reactions by applying electrical energy The least unfavorable potential reaction goes first (there can be overlap) Overpotentials and concentrated reactants are used Midterm #1 Tuesday 7 February, 7-9 PM 10 AM Lecture (Section 2, all) in Moore 100 12 noon Lecture: Sections 3A-D in Physics & Astronomy Building 1425 Sections 3E-I Lakretz 110 8 Recap of Lecture #12: Electrolytic Reactions Electrolysis Driving non-spontaneous reactions by applying electrical energy The least unfavorable potential reaction goes first (there can be overlap) NaCl(l) vs NaCl(aq) Overpotentials and concentrated reactants are used Recap of Lecture #14: Electrolysis & Acid/Base Equilibria Electrolysis: Quantify the amount of reaction – n, F, and number of moles Acids and bases HX(aq) H+(aq) + X-(aq) X-(aq) + H2O(l) + Ka = [H ][X ] [HX] HX (aq) + OH-(aq) Exam #1 average = 75 Standard dev = 17 4@104 & 21@ ≥100 -] Kb = [HX][OH [X ] Table of initial and equilibrium conditions Solve problems by following the amount of reaction Make and test assumptions about relative significance of initial concentrations and amount of reaction (our limit here will be <3%) Fractional dissociation and dilution 9 Recap of Lecture #15: Polyprotic Acids & Buffers Polyprotic Acids + H+(aq) + HX-(aq) Ka1 = [H ][HX ] [H2X] H2X(aq) HX-(aq) Exam #1 average = 75 Standard dev = 17 4@104 & 21@ ≥100 + 2Ka2 = [H ][X- ] [HX ] H+(aq) + X2-(aq) Table of initial, intermediate, and final equilibrium conditions Solve problems by following the amounts of reactions Make and test assumptions about relative significance of initial concentrations and amount of reaction (our limit here will be <3%) Buffer pH = pKa – log10 [HA] [A-] pH should be within ~1 unit of pKa How to make a buffer – acid + conjugate base Buffer capacity Recap of Lecture #16: Solubility, Peroxides, Superoxides, Amphoterism 2- - Peroxide: O2 Superoxide: O2 Disproportionation reactions An oxidizing agent oxidizes something else, and is reduced. A reducing agent reduces something else, and is oxidized. Hydride HSolubility product MaXb(s) aM+(aq) + bX-(aq) Ksp = [M+]a[X-]b In solving equilibria, keep track of stoichiometry Solubility – how much of the solid (in moles/L) dissolves in a given solution Amphoterism e.g., Al(OH)3(H2O)3 is more soluble (as an ion) in acid or base than in neutral solution - Al(OH)3(H2O)3 vs [Al(OH)2(H2O)4]+ or [Al(OH)4(H2O)2]- 10 Recap of Lecture #17: Complex Ions + Photon Absorption & Emission Solubility – Ksp Drive equilibrium by adding or removing ions (products). Common ion effect – solubility is reduced Complex ions Lewis acid – Lewis base adducts Coordination determined by central element’s orbitals Important in enzymes, catalysis, metal/salt dissolution Formation & dissociation constants → KF = 1/KD Dissolve insoluble salts Chelation – multiple Lewis base sites on one molecule Entropic advantage Metal Ion Buffer – store metal ions as complex ions Photon Absorption and Emission Basis of spectroscopy Review Session Monday 27 Feb 7-9 PM Dodd 147 Recap of Lecture #18: Fluorescence + Metals and Semiconductors Photon Absorption and Emission, Fluorescence Basis of spectroscopy Metals No band gap HOMO, LUMO are at the same energy Electronic excitation is small vs. kT High electrical and thermal conductivity Semiconductors and Insulators Have a band gap HOMO, LUMO are at different energies More now! Review Session Monday 27 Feb 7-9 PM Dodd 147 11 Lecture 20 (Kris Barr) Fluorescence, Metals, Semiconductors, and Energy Scale Midterm notes CS 50 Sections 2A-2E CS 24 Sections 2F-2L Moore 100 Lecture 3 Regrades in pen only Conflicts NEED TO BE CONFIRMED BY 1:30 TODAY Review Session Tonight Feb 7-9 PM Dodd 147 Paul’s Office Hours Tues 3:30 to 4:30 PM Recap of Lecture #20: Energy Scales, Fluorescence, Metals and Semiconductors Photon Absorption and Emission, Fluorescence Metals No band gap HOMO, LUMO are at the same energy Electronic excitation is small vs. kT (thermal energy) High electrical and thermal conductivity Midterm exam #2: CS 50 Sections 2A-2E CS 24 Sections 2F-2L Moore 100 Lecture 3 Regrades for exams taken in pen only Semiconductors and Insulators Have a band gap HOMO, LUMO are at different energies Dopants in semiconductors Elemental identity determines energy of dopant level which then determines p- or n-type Energy of dopant level and concentration determine conductivity of material more dopant atoms è higher conductivity Do not form a “band” – serve as a source or sink for thermally excited electrons Exam #2 covers through last Friday’s lecture (along with Kris’ explanations Monday): recaps and coverage at http://bit.ly/20B17recaps (also linked in syllabus) Data sheet will be nearly identical to exam #1. No calculators, phones, devices, watches, etc. 12 Recap of Lecture #23: Kinetics Kinetics Rate laws Reaction order Order and stoichiometry are not the same Clue to mechanism Reaction dynamics = kinetics + mechanism Location of reaction barrier determines effectiveness of translation vs. vibration at promoting reaction. Recall the mechanism and kinetics do NOT affect the thermodynamics (state functions) and equilibra. Reaction Order Statistical/graphical analysis of kinetics Concentration First order reactions result in exponential changes in [reactants], [products] Time Recap of Lecture #24: Kinetics Kinetics Compare thermal energy to barrier Reaction Order Statistical/graphical analysis of kinetics Early results of midterm #2: 79 ± 14 with all precincts reporting Catalysis Lower barrier to accelerate reaction Recall the mechanism and kinetics do NOT affect the thermodynamics (state functions) and equilibria Catalytic Converters – catalyze multiple reactions Oxidation: Hydrocarbons, CO → CO2 + H2O Reduction: NO, NO2 → N2 Catalysts: CuO, Cr2O3, Pt, Rh 13 Recap of Lecture #24: Kinetics/Enzymes Enzymes Biological catalysts Better specificity, turnover numbers, and control than artificial catalysts Most are proteins, and can also include co-factors (vitamins) and metal ions (There are also some RNA enzymes.) Biopolymers DNA – copolymer of four bases RNA – copolymer of four bases Proteins – Copolymer of 20 amino acids, with ~100 other chemical modifications Function depends on chemical modifications, environment, conformation Lewis base sites coordinate metals Polymerase chain reaction – enzyme to copy DNA Drugs often interfere with enzyme activity (e.g., bind up active site) Midterm #2: 79 ± 14 Recap of Lecture #26: Direct & Indirect Band Gap Semiconductors, Semi-Metals, Nuclear Decay Direct vs. indirect band gap semiconductors Direct – top of valence band aligns with bottom of conduction band light is efficiently coupled in & out - photodetectors, photodiodes, LEDs, lasers e.g., GaAs Indirect – direct band gap is larger than indirect gap, misaligned bands inefficient coupling of light e.g., Si, Ge Semi-metal – no band gap, but 0 density of states at EFermi Nuclear Stability Unstable elements decay so as to move toward the band of stability Transuranium elements undergo a series of alpha decays Neutron-rich isotopes undergo beta decays Neutron-deficient isotopes undergo positron emission or electron capture Even proton and neutron numbers + closed shells favor stability Radioactive Dating First-order (exponential) decay kinetics Measure elapsed time by following decay of an isotope Example – 14C decay measures the time since respiration stopped (end of carbon uptake) 14C half-life of 5700 years, 238U half-life of 4.5x109 years Accessible ages must be on these scales After n half-lives, (½)n of original amount remains 14 Recap of Lecture #27: Nuclear Reactions II Mass Defect ΔE = Δmc2 Energy scales are much higher than chemical energies (KNOW THEM!) Exothermic Nuclear Reactions Rate stability as mass deficit per nucleon. Binding energy per nucleon peaks at 56Fe Lighter elements can undergo fusion exothermically Heavier elements can undergo fission exothermically Nuclear Chain Reactions More neutrons produced than absorbed Subcritical mass – not sustained Critical mass – self-sustaining reaction Supercritical mass – increasing reaction rate – bomb Nuclear Reactors Fission reactors – most common Heat water to drive steam turbines Use moderators to determine neutron capture rate and thus reaction rate Breeder reactors produce more fuel than they consume Fusion reactors do not exist due to difficulty in sustaining high temperatures required Exam #2 Topics (in order of requests to review) Materials – semiconductors, insulators, and metals Semiconductors: Density of states, dopants Fluorescence, energy scales, spectroscopy Complex ions & chelates Solubility Disproportionation reactions Amphoterism Buffers Acid/base equilibria Polyprotic acids Electrolytic reactions Quantifying the amount of electrochemical reaction Peroxide, superoxide, hydride Oxidizing and reducing agents 15 Recap of Lecture #27: Nuclear Reactions II Mass Defect ΔE = Δmc2 Energy scales are much higher than chemical energies (KNOW THEM!) Exothermic Nuclear Reactions Rate stability as mass deficit per nucleon. Binding energy per nucleon peaks at 56Fe Lighter elements can undergo fusion exothermically Heavier elements can undergo fission exothermically Nuclear Chain Reactions More neutrons produced than absorbed Subcritical mass – not sustained Critical mass – self-sustaining reaction Supercritical mass – increasing reaction rate – bomb Nuclear Reactors Fission reactors – most common Heat water to drive steam turbines Use moderators to determine neutron capture rate and thus reaction rate Breeder reactors produce more fuel than they consume Fusion reactors do not exist due to difficulty in sustaining high temperatures required Final Exam Comprehensive Final Exam Tuesday 21 March 630-930 PM CS 24 Sections 2E-2L CS 50 Sections 2A-2D & 3A-C CS 76 Sections 3D-3I Those who are taking a make-up exam were set up last week (Friday 3-6 PM, CS50 – calculators ok on make-up only, be sure to get extra questions) TA Review Session: Saturday 18 March, 2-4 PM in CS76 Homework Assessments Two midterm scores Final exam 25% 10% 40% 25% Please complete your course evaluations by Saturday 8 AM Please feel free to send me comments and suggestions directly Office hours next week: Tuesday 1030-1130 AM, 230-330 PM &Thursday 230-330 PM 1 Nuclear Binding Energy Sholto Ainslie Design, Wordpress Data from NASA Goddard Thermodynamics and Equilibria Thermodynamics, free energy (ΔG), enthalpy (ΔH), entropy (ΔS), cell potential (E) Use intuition, rules of forming stronger bonds (ΔH<0) Entropy changes – gas/solution/liquid/solid Know sign conventions Relate thermodynamics, equilibrium constants, and electrochemistry (vs kinetics) Phase transitions Acids & bases, buffers Solubility Complex formation – Lewis acid – Lewis base interactions (including enzymes) Periodic trends Interaction strengths Chemical bonds – covalent, ionic, metallic Weaker interactions – hydrogen bonding, ion-dipole, dipole-dipole, Electrochemistry – LAnOx & GRedCat Oxidation states, half reactions, spontaneous & non-spontaneous reactions Batteries, electrolysis 2 Kinetics Rate laws Reaction order Order and stoichiometry are not the same Clue to mechanism Reaction dynamics = kinetics + mechanism Location of reaction barrier determines effectiveness of translation vs. vibration at promoting reaction Recall the mechanism and kinetics do NOT affect the thermodynamics (state functions) and equilibra Reaction Order Statistical/graphical analysis of kinetics Catalysis Lower barrier to accelerate reaction equilibration Recall the mechanism and kinetics do NOT affect the thermodynamics (state functions) and equilibra Enzymes are biological catalysts with greater specificity and control than synthetic catalysts Materials Semiconductors Conduction and valence bands Band gap, Fermi level Density of states n- and p-type, semi-insulating Direct and indirect band gaps Reactions of Si to make: insulators, metals, and to add dopants Conductivity increases with increasing temperature thermal excitation to conduction band or from valence band Insulators Conductivity increases with increasing temperature Energy level diagram looks like semiconductor but bigger gap (compare to kT) Metals No band gap Conductivity decreases with increasing temperature 3 Nuclear Chemistry Decays - α, β-, β+, γ, electron capture Balance decay reactions Band of stability – also, use periodic table (what are average/common masses?) Nuclear Stability Unstable elements decay so as to move toward the band of stability Transuranium elements undergo a series of α decays Neutron-rich isotopes undergo β- decays Neutron-deficient isotopes undergo positron emission or electron capture Even proton and neutron numbers + closed shells favor stability Radioactive Dating First-order (exponential) decay kinetics Measure elapsed time by following decay of an isotope Example – 14C decay measures the time since respiration stopped (end of carbon uptake) 14C half-life of 5700 years, 238U half-life of 4.5x109 years Accessible ages must be on these scales After n half-lives, (½)n of original amount remains Nuclear Energy Mass defect, ΔE = Δmc2 – binding energy per nucleon peaks at 56Fe Fission and chain reactions, fusion Chemical Measurements Infrared spectroscopy – vibrations, chemical fingerprint Optical and ultraviolet spectroscopy – electronic excitation X-ray spectroscopies – core levels, elemental identification Fluorescence Mass spectrometry Electrochemical – thermodynamics Balance cells and half-cells, count electrons Quantitative Also important in energy harvesting and storage X-ray diffraction – spacings in and between molecules Microscopies – real-space measurements Know energy scales, both for photons and interaction strengths 4 Photon Energies Infrared spectroscopy – vibrations, chemical fingerprint Optical and ultraviolet spectroscopy – electronic excitation X-ray spectroscopies – core levels, elemental identification X-ray diffraction – bond lengths in crystals (Microwave spectroscopy – rotations) NASA, via Earth & Sky 5 Exam #2 Review Materials Semiconductors Conduction and valence bands Band gap, Fermi level Density of states n- and p-type, semi-insulating Direct and indirect band gaps Reactions of Si to make: insulators, metals, and to add dopants Conductivity increases with increasing temperature thermal excitation to conduction band or from valence band EFermi Insulators Conductivity increases with increasing temperature Energy level diagram looks Metals No band gap Conductivity decreases with increasing temperature – scattering of carriers Exam #2 Review Energy scales Reaction free energy changes and interaction strengths vs. photon energies Measurements & spectroscopies Energies and wavelengths e.g., for diffraction, we match photon wavelength to bond length choose X-rays (not yet covered) Infrared – vibrational transitions è Useful for chemical identification of functional groups (e.g., -CH3) Visible & near UV – electronic transitions (not generally used for chemical ID) X-ray – core level electronic excitations è Useful for identifying elements, Li and beyond 16 Exam #2 Review Buffers and acid/base equilibria HA H+ + A- Ka = [H+][A-] [HA] pKa = -log10Ka pH = pKa – log10 [HA] [A-] pH should be within 1 unit of pKa The more of the acid and base present, the greater the capacity of the buffer Exam #2 Review Solubility MaXb(s) aM+(aq) + bX-(aq) Ksp = [M+]a[X-]b Solubility of a solid in a specific solution – how much dissolves in moles/L Equilibria, LeChatelier’s Principle, Common Ion Effect, and è Complex Ion Formation Lewis acid-base adducts Chelation and the effect of entropy in polydentate ligands Use complex ions to dissolve solids or to supply/buffer metal ions where they are needed in solution Relate thermodynamics, equilibrium constants, and electrochemistry (vs. kinetics) Amphoterism – charged hydroxides are more soluble than neutral species e.g., Al(OH)3(H2O)3 vs [Al(OH)2(H2O)4]+ or [Al(OH)4(H2O)2]- 17 Exam #2 Review 2- - Peroxide: O2 Superoxide: O2 Disproportionation reactions An oxidizing agent oxidizes something else, and is reduced. A reducing agent reduces something else, and is oxidized. Hydride H- Additional Slides Here are a few additional slides for reference 18 Intramolecular and Intermolecular Potentials PoMC, Oxtoby, Gillis, & Campion Transformations: Energy and Order Forming or breaking bonds? Breaking bonds costs energy (ΔH). Which state is more ordered (ΔS)? We will come back to this topic quantitatively (Ch. 12) http://ch302.cm.utexas.edu/physEQ/physical/physical-all.php 19 Real Gases – corrected figure labels on left Deviations from ideal gas Repulsive forces (volume) PV RT For N2 Attractive forces (when close together) P (atm) PV RT P (atm) wps.prenhall.com Heat Water, Starting from Ice Add heat to go from ice to water to steam http://ch302.cm.utexas.edu/physEQ/physical/physical-all.php 20 Periodic Trends Reminder Periodic Trends Know which direction across the periodic table determines property. Based on filling electron shells Ionization Energy ì Low if resulting ion has filled shell rare gas configuration. (or to a lesser extent – has filled or half-filled subshells) Same rules for higher oxidation states (e.g., Mg+2) Electron Affinities í (Negative values for species with stable anions) Related to electronegativity ì – many ways to define this. Determine dipoles within molecules. Atomic & Ionic Sizes í Size decreases with more positive oxidation state for isoelectronic atoms/ions. . Le Chatelier’s Principle Disturb a system from equilibrium and it will move back to restore that equilibrium Increase a concentration è reaction shifts to decrease (consume) what was added Increase pressure è reaction shifts to consume gas + more This concept is used to drive reactions – by removing one or more of the products cf. homeostasis Stay tuned for buffers 21 Solution Compositions Concentrations Most common is molarity M = moles solute / L solution Water is 55.5 M K2SO4(s) H2O 2K+ + SO42- Since K2SO4 is soluble in water, 1 M K2SO4(aq) is 2 M K+ and 1 M SO42Others used: Mole fraction = moles of X / total moles Mass percentage is common in everyday life Less common are: Normality = equivalents (usually acid or base) / L Still used in medicine, but discouraged in science & engineering Molality = moles solute / kg solvent . Balancing Reactions Same number of atoms of each element on each side of reaction* Same total charge on each side In electrochemistry – we will also cover half-cell reactions. In reduction, electrons will be a reactant (on left) In oxidation, electrons will be a product (on right) Total reaction will eliminate electrons from both sides. Losing electrons at Anode is Oxidation & Gaining electrons is Reduction at the Cathode LAnOx & GRedCat *Except in nuclear reactions . 22 Intermolecular and Intramolecular Forces I All based on Coulomb’s Law (interacting charges) www.umkc.edu Intermolecular and Intramolecular Forces II All based on Coulomb’s Law (interacting charges) www.umkc.edu 23 Effect of Concentration on E and ΔG Half Reactions aA + bB + ne° – E1/2 = E1/2 cC + dD [C]c[D]d 2.303RT log10 [A]a[B]b nF Cell Reactions aA + bB cC + dD ° – Ecell = Ecell [C]c[D]d 2.303RT log10 [A]a[B]b nF ΔG = ΔG° + 2.303 RT log10 [C]c[D]d [A]a[B]b At equilibrium: ΔG = 0, so: ΔG° = –2.303 RT log10Keq Buffers slideshare.com 24 Metal Complexes Coordination compounds Lewis acid – Lewis base adducts Important in enzymes, catalysis, metal/salt dissolution Orbitals and oxidation state of central metal ion determine coordination. Electronic excitation – absorption and emission Lewis base ligands split electronic energies of metal ions – leading to color and spin Lone pair electrons repel and stay farthest away (as compared to ligands) Spin High spin vs. low spin compounds Compare crystal field splitting (Δ) to the spin pairing energy (P) Spectrochemical series – relative ligand effect on Δ Paramagnetic – having one of more unpaired spins Colors Complementary colors – if a color is absorbed, the absorbing material will appear as the complementary color Red-green, orange-blue, yellow-violet Other means of color: emission, interference Energy and Excitations in Solids Metals No band gap - HOMO, LUMO are at the same energy Electronic excitation is small vs. kT High electrical and thermal conductivity Conductivity decreases with increasing temperature because of electron scattering Semiconductors and Insulators Have a band gap between valence (lower) band and conduction (upper) band – electronic excitation is >kT This determines insulator vs. semiconductor Direct band gap can be excited by photons (very little momentum) Indirect band gap cannot be photoexcited efficiently Electrons and “holes” can carry charge Differentiate with magnetic field (Hall effect) Energies of (dopant) states in the band gap determine conductivity and whether electrons or holes dominate current Conductivity increases with increasing temperature because of thermal excitation of carriers 25 Semiconductor Electronic Structure Semiconductor (intrinsic) Raising temperature increases conductivity (i.e., decreases resistivity), because carriers are thermally excited EFermi With impurities, semiconductors have shifted Fermi energies, from/to which carriers can be thermally excited wikipedia.com Doping in Semiconductors Thermally excite carriers from/to dopant level in the band gap Semiconductor Semiconductor p-type n-type EFermi EFermi 26 Direct vs. Indirect Band Gap Semiconductors Energy and momentum are conserved in photoexcitation Photons carry little momentum Direct band gap semiconductors absorb and emit light more efficiently than indirect band gap semiconductors Indirect Band Gap Semiconductor Direct Band Gap Semiconductor Conduction Band E Conduction Band E Direct band gap Valence Band Valence Band Momentum Momentum e.g., Si, Ge e.g., GaAs, GaN Semimetals Semimetals have no band gap, but no states at the Fermi energy e.g., graphite, graphene Peplow, Nature 503, 327 (2013) Millie Dresselhaus MIT ? Kostya Novoselov Manchester 27 Band of Stability for Nuclei arpansa.gov.au/radiationprotection Example Examinations Note that the syllabus has changed and there are different numbers of exams. Averages for the exams shown: Exam #1: 62 Exam #2: 79 Exam #3: 63 Final Exam: 87 28 Name _______________________ Section # ____ Student ID # ___________ Chemistry 20B, Winter 2016, Sections 1 & 3, Midterm #1 20 January 2016 6 questions + 2 small extra credit problems, 10 pages. Answer on these sheets only. Additional space on last page. If you need extra sheets, please ask your proctor or TA. Note: Only these papers can be used; no other notes are allowed. Please answer each question concisely. Show your calculations. You may (and in some cases, must) draw explanatory diagrams. Label all axes and features on graphs and diagrams. You may not use a calculator, computer, watch, smart device, or electronics of any sort. Irrelevant material will be ignored. Incorrect material will result in loss of points. Table of constants and conversions Speed of light: c = 3 × 108 m/s Electron charge magnitude: e = 1.6 × 10-19 C Plank's constant: ℏ = 1.1 × 10-34 J-s Gas constant: R = 0.08206 L-atm/mol-K = 8.314 J/mol-K = 1.987 cal/mol-K Boltzmann constant: kB = 1.4 × 10-23 J/K Electron rest mass: m = 9.1 × 10-31 kg Proton rest mass: M = 1.7 × 10-27 kg 1 mole = 6.02 × 1023 You will find a periodic table for your reference on the next page. 1 1 2 3 13 5 10.811 GROUP CAS RELATIVE ATOMIC MASS (1) GROUP IUPAC ATOMIC NUMBER B 1 2 Nonmetal 16 Chalcogens element Semimetal Alkali metal 17 Halogens element Metal Alkaline earth metal - gas 58.693 - liquid VIIIB 9 10 27 58.933 28 Ne Ga 11 29 Fe Tc IB 12 30 63.546 - synthetic - solid STANDARD STATE (100 °C; 101 kPa) 18 Noble gas Lanthanide Transition metals 55.845 Actinide VIB 7 VIIB 8 25 54.938 26 51.996 65.39 IIIA 14 6 10.811 IVA 15 7 12.011 VA 16 8 14.007 VIA 17 9 15.999 VIIA 18.998 18 VIIIA 2 4.0026 He 20.180 HELIUM 10 Ne 39.948 F 18 O 35.453 N 17 C 32.065 B 16 NEON 30.974 FLUORINE 15 OXYGEN 28.086 NITROGEN 14 CARBON 26.982 BORON 54 131.29 KRYPTON Kr 83.80 Ar 126.90 36 Cl 79.904 S 53 BROMINE Br 35 P 78.96 Si 34 Al 74.922 ARGON 33 CHLORINE 72.64 SULPHUR 32 PHOSPHORUS 69.723 SILICON 31 ALUMINIUM 13 13 5 PERIODIC TABLE OF THE ELEMENTS IIA 9.0122 GROUP 2 4 http://www.ktf-split.hr/periodni/en/ 1.0079 H 6.941 SYMBOL BORON ELEMENT NAME VB 6 24 50.942 IIB IA 1 1 3 HYDROGEN Be 24.305 Li 12 BERYLLIUM 22.990 LITHIUM 11 MAGNESIUM Na Mg SODIUM IVB 5 23 Se 47.867 As IIIB 4 22 44.956 Ge 3 21 Ga 40.078 Zn 20 Cu 39.098 Ni 19 Co 127.60 Fe 52 Cr Mn 121.76 V 51 Ti 118.71 Sc 50 Xe 114.82 I 49 Te 112.41 Sb 48 Sn RADON Rn (222) At 86 ASTATINE (210) Po 85 POLONIUM (209) Bi 69 168.93 70 173.04 MENDELEVIUM 102 (259) 174.97 (262) NOBELIUM LAWRENCIUM Lr 103 LUTETIUM Lu 71 Copyright © 1998-2003 EniG. ([email protected]) BISMUTH (289) 167.26 Pb 114 Uuq 164.93 UNUNQUADIUM 67 68 Tl 162.50 LEAD 66 THALLIUM 84 In (285) MERCURY 112 UNUNBIUM 158.93 (258) YTTERBIUM Er Tm Yb 101 THULIUM ERBIUM (257) FERMIUM Fm Md No 100 Ho (252) HOLMIUM 99 Dy (251) Es BERKELIUM CALIFORNIUM EINSTEINIUM Cf 98 DYSPROSIUM (247) Tb 97 TERBIUM 65 208.98 Cd (272) 157.25 (247) 83 Ag 64 Gd 96 207.2 Pd 151.96 (243) 82 Rh 63 95 204.38 XENON 150.36 (244) CURIUM 81 IODINE 200.59 TELLURIUM 80 ANTIMONY 196.97 TIN 111 GOLD Au Hg 79 INDIUM 195.08 CADMIUM 78 SILVER 192.22 PALLADIUM 77 RHODIUM 107.87 Ca 190.23 47 K 76 106.42 SELENIUM 186.21 46 ARSENIC 75 102.91 GERMANIUM 183.84 45 GALLIUM 101.07 Ru 44 ZINC (98) Tc 43 COPPER 95.94 NICKEL 42 COBALT 92.906 74 MOLYBDENUM TECHNETIUM RUTHENIUM Pt 180.95 Ir 73 NIOBIUM Nb Mo 41 IRON 91.224 CHROMIUM MANGANESE 40 VANADIUM 88.906 TITANIUM 39 SCANDIUM 87.62 CALCIUM Zr 38 Y 85.468 POTASSIUM Sr 37 Rb ZIRCONIUM Os 178.49 57-71 YTTRIUM Re (281) W 110 Ta (268) Hf 62 MEITNERIUM UNUNNILIUM UNUNUNIUM Mt Uun Uuu Uub 109 PLATINUM (277) IRIDIUM 108 OSMIUM (264) RHENIUM 107 Hs (266) TUNGSTEN HASSIUM 106 Bh (262) TANTALUM BOHRIUM 105 Sg (145) SEABORGIUM 61 Db 144.24 DUBNIUM 60 Rf 140.91 94 EUROPIUM GADOLINIUM Nd Pm Sm Eu (237) AMERICIUM Pu Am Cm Bk NEPTUNIUM PLUTONIUM Np 93 PRASEODYMIUM NEODYMIUM PROMETHIUM SAMARIUM Pr 59 RUTHERFORDIUM (261) HAFNIUM 72 137.33 56 STRONTIUM 132.91 Actinide Ac-Lr 89-103 104 Lanthanide La-Lu RUBIDIUM Ba 55 Cs (226) BARIUM Ra 88 RADIUM (223) CAESIUM Fr 87 FRANCIUM 140.12 Ce 58 CERIUM 138.91 La 57 LANTHANIDE LANTHANUM 238.03 U 92 URANIUM 231.04 Pa 91 PROTACTINIUM 232.04 Th 90 THORIUM (227) Ac 89 ACTINIDE ACTINIUM 2 4 5 6 7 Editor: Aditya Vardhan ([email protected]) However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. Relative atomic mass is shown with five significant figures. For elements have no stable nuclides, the value enclosed in brackets indicates the mass number of the longest-lived isotope of the element. (1) Pure Appl. Chem., 73, No. 4, 667-683 (2001) PERIOD Question 1 (10 points): In Flint, Michigan, the water supply has become contaminated with lead. If you were worried that other metals might be in the water, how would you determine which are present? Describe how that information is obtained from your choice. Question 2 (15 points): A 3-m long cylinder has three compartments with two and each compartment has a volume of 45 L. Initially, the separators are held in place and each compartment is open to the air, with the pressure in the room at 760 torr (1.0 atm), and the temperature at 0 °C. Assume that the air is an ideal gas. a) How many moles of gas are in each compartment? (5 points) b) The connections from the compartments to the room are sealed off and: the pressure in the right chamber is increased to 2.0 atm, the pressure in the left chamber is increased to 3.0 atm, and then the separators (pistons) are released and move without friction. What is the pressure in each chamber? Where do the separators sit (draw a diagram) and why? (10 points) Question 3 (30 points): Heat is added at a constant rate to water as the temperature is raised from -20 °C to 120 °C. Draw the time course of the temperature and density (two different curves) and indicate the phase(s) at each temperature. Label and concisely explain each stage of each curve and indicate where intermolecular bonds are made or broken. Question 4 (15 points): How could you differentiate between ethylene (C2H4), nitrogen (N2), and carbon monoxide (CO) using mass spectrometry? Question 5 (15 points): Why are there warning signs indicating “ionizing radiation”? Briefly explain in terms of energies and other related issues. Give two examples of ionizing radiation. Question 6 (15 points): How would you experimentally determine the atomic radius of Xe? Briefly explain your choice of technique in terms of length scales, energies, and related issues. Extra credit #1 (2 points): How are the gas constant, R, and the Boltzmann constant, kB, conceptually related Extra credit #2 (2 points): How are the energy units Hz and cm-1 conceptually related? 3 Name _______________________ Section # ____ Student ID # ___________ TOTAL = ________ Chemistry 20B, Winter 2016, Sections 1 & 3, Midterm #2 18 February 2016 5 questions + 2 small extra credit problems, 10 pages. Answer on these sheets only. Additional space on last page. If you need extra sheets, please ask your proctor or TA. 1) Note: Only these papers can be used; no other notes are allowed. 4) Please answer each question concisely. Show your calculations. You may (and in some cases, must) draw explanatory diagrams. Label all axes and features on graphs and diagrams. 5) 2) 3) EC1+2) You may not use a calculator, computer, watch, smart device, or electronics of any sort. Irrelevant and/or incorrect material will result in loss of points. Table of constants and conversions Speed of light: c = 3 × 108 m/s Electron charge magnitude: e = 1.6 × 10-19 C Plank's constant: ℏ = 1.1 × 10-34 J-s Gas constant: R = 0.08206 L-atm/mol-K = 8.314 J/mol-K = 1.987 cal/mol-K Boltzmann constant: kB = 1.4 × 10-23 J/K Electron rest mass: m = 9.1 × 10-31 kg Proton rest mass: M = 1.7 × 10-27 kg 1 mole = 6.02 × 1023 ΔG° = -nFE° = -2.303 RT log10Keq pH = pKa – log10 ([HA]/[A-]) You will find a periodic table for your reference on the next page. 1 1 2 3 13 5 10.811 GROUP CAS RELATIVE ATOMIC MASS (1) GROUP IUPAC ATOMIC NUMBER B 1 2 Nonmetal 16 Chalcogens element Semimetal Alkali metal 17 Halogens element Metal Alkaline earth metal - gas 58.693 - liquid VIIIB 9 10 27 58.933 28 Ne Ga 11 29 Fe Tc IB 12 30 63.546 - synthetic - solid STANDARD STATE (100 °C; 101 kPa) 18 Noble gas Lanthanide Transition metals 55.845 Actinide VIB 7 VIIB 8 25 54.938 26 51.996 65.39 IIIA 14 6 10.811 IVA 15 7 12.011 VA 16 8 14.007 VIA 17 9 15.999 VIIA 18.998 18 VIIIA 2 4.0026 He 20.180 HELIUM 10 Ne 39.948 F 18 O 35.453 N 17 C 32.065 B 16 NEON 30.974 FLUORINE 15 OXYGEN 28.086 NITROGEN 14 CARBON 26.982 BORON 54 131.29 KRYPTON Kr 83.80 Ar 126.90 36 Cl 79.904 S 53 BROMINE Br 35 P 78.96 Si 34 Al 74.922 ARGON 33 CHLORINE 72.64 SULPHUR 32 PHOSPHORUS 69.723 SILICON 31 ALUMINIUM 13 13 5 PERIODIC TABLE OF THE ELEMENTS IIA 9.0122 GROUP 2 4 http://www.ktf-split.hr/periodni/en/ 1.0079 H 6.941 SYMBOL BORON ELEMENT NAME VB 6 24 50.942 IIB IA 1 1 3 HYDROGEN Be 24.305 Li 12 BERYLLIUM 22.990 LITHIUM 11 MAGNESIUM Na Mg SODIUM IVB 5 23 Se 47.867 As IIIB 4 22 44.956 Ge 3 21 Ga 40.078 Zn 20 Cu 39.098 Ni 19 Co 127.60 Fe 52 Cr Mn 121.76 V 51 Ti 118.71 Sc 50 Xe 114.82 I 49 Te 112.41 Sb 48 Sn RADON Rn (222) At 86 ASTATINE (210) Po 85 POLONIUM (209) Bi 69 168.93 70 173.04 MENDELEVIUM 102 (259) 174.97 (262) NOBELIUM LAWRENCIUM Lr 103 LUTETIUM Lu 71 Copyright © 1998-2003 EniG. ([email protected]) BISMUTH (289) 167.26 Pb 114 Uuq 164.93 UNUNQUADIUM 67 68 Tl 162.50 LEAD 66 THALLIUM 84 In (285) MERCURY 112 UNUNBIUM 158.93 (258) YTTERBIUM Er Tm Yb 101 THULIUM ERBIUM (257) FERMIUM Fm Md No 100 Ho (252) HOLMIUM 99 Dy (251) Es BERKELIUM CALIFORNIUM EINSTEINIUM Cf 98 DYSPROSIUM (247) Tb 97 TERBIUM 65 208.98 Cd (272) 157.25 (247) 83 Ag 64 Gd 96 207.2 Pd 151.96 (243) 82 Rh 63 95 204.38 XENON 150.36 (244) CURIUM 81 IODINE 200.59 TELLURIUM 80 ANTIMONY 196.97 TIN 111 GOLD Au Hg 79 INDIUM 195.08 CADMIUM 78 SILVER 192.22 PALLADIUM 77 RHODIUM 107.87 Ca 190.23 47 K 76 106.42 SELENIUM 186.21 46 ARSENIC 75 102.91 GERMANIUM 183.84 45 GALLIUM 101.07 Ru 44 ZINC (98) Tc 43 COPPER 95.94 NICKEL 42 COBALT 92.906 74 MOLYBDENUM TECHNETIUM RUTHENIUM Pt 180.95 Ir 73 NIOBIUM Nb Mo 41 IRON 91.224 CHROMIUM MANGANESE 40 VANADIUM 88.906 TITANIUM 39 SCANDIUM 87.62 CALCIUM Zr 38 Y 85.468 POTASSIUM Sr 37 Rb ZIRCONIUM Os 178.49 57-71 YTTRIUM Re (281) W 110 Ta (268) Hf 62 MEITNERIUM UNUNNILIUM UNUNUNIUM Mt Uun Uuu Uub 109 PLATINUM (277) IRIDIUM 108 OSMIUM (264) RHENIUM 107 Hs (266) TUNGSTEN HASSIUM 106 Bh (262) TANTALUM BOHRIUM 105 Sg (145) SEABORGIUM 61 Db 144.24 DUBNIUM 60 Rf 140.91 94 EUROPIUM GADOLINIUM Nd Pm Sm Eu (237) AMERICIUM Pu Am Cm Bk NEPTUNIUM PLUTONIUM Np 93 PRASEODYMIUM NEODYMIUM PROMETHIUM SAMARIUM Pr 59 RUTHERFORDIUM (261) HAFNIUM 72 137.33 56 STRONTIUM 132.91 Actinide Ac-Lr 89-103 104 Lanthanide La-Lu RUBIDIUM Ba 55 Cs (226) BARIUM Ra 88 RADIUM (223) CAESIUM Fr 87 FRANCIUM 140.12 Ce 58 CERIUM 138.91 La 57 LANTHANIDE LANTHANUM 238.03 U 92 URANIUM 231.04 Pa 91 PROTACTINIUM 232.04 Th 90 THORIUM (227) Ac 89 ACTINIDE ACTINIUM 2 4 5 6 7 Editor: Aditya Vardhan ([email protected]) However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. Relative atomic mass is shown with five significant figures. For elements have no stable nuclides, the value enclosed in brackets indicates the mass number of the longest-lived isotope of the element. (1) Pure Appl. Chem., 73, No. 4, 667-683 (2001) PERIOD Question 1 (25 points): Limestone (CaCO3) is heated to produce lime (CaO) as an inexpensive, solid base in the following reaction: CaCO3(s) → CaO(s) + CO2(g) a) What are the signs of ΔH, ΔS, and ΔG for this reaction? (20 points) Explain your answer for each. If any of the answers depend on additional information, indicate on what and how. b) What can you say about the equilibrium constant Keq? (5 points) Question 2 (15 points): Referring again to the reaction: CaCO3(s) → CaO(s) + CO2(g) a) Write the equilibrium constant for this reaction (in terms of concentrations, etc.). (5 points) b) If a sealed container, initially under vacuum, with both CaCO3(s) and CaO(s) inside is allowed to reach equilibrium, how might you measure the equilibrium constant? (5 points) c) When the volume of the container is doubled (by opening a valve to an evacuated container), what happens? (5 points) Question 3 (20 points): On the first exam, you described what happened when heat is added at a constant rate to water as the temperature is raised from -20 °C to 120 °C. a) Draw the time course of the temperature again. Indicate the phase(s) present in each temperature band. Indicate what determines the slope for each section of the plot. (10 points) b) Describe briefly what we know (i.e., signs and any other information) about ΔH, ΔS, and ΔG at each phase transition? (10 points) 3 Question 4 (25 points): A lithium ion battery, such as found in a cell phone, operates at a high cell potential based on the following half-cell reactions: CoO2 + Li+ + e− ↔ LiCoO2 E° ≅ 1 V Li+ + C6(polymer/graphite) + e− ↔ LiC6(polymer/graphite) E° ≅ -3 V Compare to: O2(g) + 4H+ + 4e− ↔ 2H2O 2H+ + 2e− ↔ H2(g) Li+ + e− ↔ Li E° = 1.23 V E° = 0.00 V E° ≅ -3 V a) What is the overall cell reaction for the lithium ion battery shown? (5 points) b) What is the overall standard cell potential of the reaction you wrote in (a)? (5 points) c) What is the n (number of electrons) for the overall cell reaction you wrote in (a)? (5 points) c) Which elements of which compounds are being oxidized and which are being reduced in the overall cell reaction you wrote in (a)? Determine the oxidation states of all the species in the reaction. (5 points) d) Can the reaction that you wrote in (a) be carried out in water (aqueous solution)? Why or why not? (5 points) Question 5 (15 points): a) Why do metals absorb infrared light (i.e., why are they not transparent in the infrared)? (5 points) b) ZnO is a direct band gap semiconductor with a band gap of 3.3 eV. Why is it colorless? (10 points, and see extra credit problem) Extra credit #1 (5 points): Why is ZnO used in sunscreen? Extra credit #2 (5 points): Estimate ΔG° for your answer to question 4b and explain your reasoning. 4 Name _______________________ Section # ____ Student ID # ___________ Signature ____________________ TOTAL = ________ Chemistry 20B, Winter 2016, Sections 1 & 3, Midterm #3 29 February 2016 5 questions + 2 small extra credit problems, 10 pages. Answer on these sheets only. Additional space on last page. If you need extra sheets, please ask your proctor or TA. 1) Note: Only these papers can be used; no other notes are allowed. 4) Please answer each question concisely. Show your calculations. You may (and in some cases, must) draw explanatory diagrams. Label all axes and features on graphs and diagrams. 5) 2) 3) EC1+2) You may not use a calculator, computer, watch, smart device, or electronics of any sort. Irrelevant and/or incorrect material will result in loss of points. Table of constants and conversions Speed of light: c = 3 × 108 m/s Electron charge magnitude: e = 1.6 × 10-19 C Plank's constant: ℏ = 1.1 × 10-34 J-s Gas constant: R = 0.08206 L-atm/mol-K = 8.314 J/mol-K = 1.987 cal/mol-K Boltzmann constant: kB = 1.4 × 10-23 J/K Electron rest mass: m = 9.1 × 10-31 kg Proton rest mass: M = 1.7 × 10-27 kg 1 mole = 6.02 × 1023 Faraday constant = 96500 coul/mole ΔG° = -nFE° = -2.303 RT log10Keq pH = pKa – log10 ([HA]/[A-]) You will find a periodic table for your reference on the next page. 1 1 2 3 13 5 10.811 GROUP CAS RELATIVE ATOMIC MASS (1) GROUP IUPAC ATOMIC NUMBER B 1 2 Nonmetal 16 Chalcogens element Semimetal Alkali metal 17 Halogens element Metal Alkaline earth metal - gas 58.693 - liquid VIIIB 9 10 27 58.933 28 Ne Ga 11 29 Fe Tc IB 12 30 63.546 - synthetic - solid STANDARD STATE (100 °C; 101 kPa) 18 Noble gas Lanthanide Transition metals 55.845 Actinide VIB 7 VIIB 8 25 54.938 26 51.996 65.39 IIIA 14 6 10.811 IVA 15 7 12.011 VA 16 8 14.007 VIA 17 9 15.999 VIIA 18.998 He 18 VIIIA 2 4.0026 20.180 HELIUM 10 Ne 39.948 F 18 O 35.453 N 17 C 32.065 B 16 NEON 30.974 FLUORINE 15 OXYGEN 28.086 NITROGEN 14 CARBON 26.982 BORON 83.80 Ar 36 Cl 79.904 S 35 P 78.96 Si 34 Al 74.922 ARGON 33 CHLORINE 72.64 SULPHUR 32 PHOSPHORUS 69.723 SILICON 31 ALUMINIUM 13 13 5 http://www.ktf-split.hr/periodni/en/ IIA 9.0122 PERIODIC TABLE OF THE ELEMENTS 2 4 IA 1.0079 H 6.941 SYMBOL BORON ELEMENT NAME VB 6 24 50.942 IIB GROUP 1 1 3 HYDROGEN Be 24.305 Li 12 BERYLLIUM 22.990 LITHIUM 11 Na Mg IVB 5 23 Kr 47.867 Br IIIB 4 22 44.956 Se 3 21 As 40.078 Ge 20 MAGNESIUM Ga 39.098 SODIUM Zn 19 Cu 131.29 Ni 54 Co 126.90 Fe 53 Cr Mn 127.60 V 52 Ti 121.76 Sc 51 Ca 118.71 K 50 Xe 114.82 I 49 Te 112.41 Sb 48 Sn RADON Rn (222) At 86 ASTATINE (210) Po 85 POLONIUM (209) Bi 69 168.93 70 173.04 MENDELEVIUM 102 (259) 174.97 (262) NOBELIUM LAWRENCIUM Lr 103 LUTETIUM Lu 71 Copyright © 1998-2003 EniG. ([email protected]) BISMUTH (289) 167.26 Pb 114 Uuq 164.93 UNUNQUADIUM 67 68 Tl 162.50 LEAD 66 THALLIUM 84 In (285) MERCURY 112 UNUNBIUM 158.93 (258) YTTERBIUM Er Tm Yb 101 THULIUM ERBIUM (257) FERMIUM Fm Md No 100 Ho (252) HOLMIUM 99 Dy (251) Es BERKELIUM CALIFORNIUM EINSTEINIUM Cf 98 DYSPROSIUM (247) Tb 97 TERBIUM 65 208.98 Cd (272) 157.25 (247) 83 Ag 64 Gd 96 207.2 Pd 151.96 (243) 82 Rh 63 95 204.38 XENON 150.36 (244) CURIUM 81 IODINE 200.59 TELLURIUM 80 ANTIMONY 196.97 TIN 111 GOLD Au Hg 79 INDIUM 195.08 CADMIUM 78 SILVER 192.22 PALLADIUM 77 RHODIUM 107.87 KRYPTON 190.23 47 BROMINE 76 106.42 SELENIUM 186.21 46 ARSENIC 75 102.91 GERMANIUM 183.84 45 GALLIUM 101.07 Ru 44 ZINC (98) Tc 43 COPPER 95.94 NICKEL 42 COBALT 92.906 74 MOLYBDENUM TECHNETIUM RUTHENIUM Pt 180.95 Ir 73 NIOBIUM Nb Mo 41 IRON 91.224 CHROMIUM MANGANESE 40 VANADIUM 88.906 TITANIUM 39 SCANDIUM 87.62 CALCIUM Zr 38 Y 85.468 POTASSIUM Sr 37 Rb ZIRCONIUM Os 178.49 57-71 YTTRIUM Re (281) W 110 Ta (268) Hf 62 MEITNERIUM UNUNNILIUM UNUNUNIUM Mt Uun Uuu Uub 109 PLATINUM (277) IRIDIUM 108 OSMIUM (264) RHENIUM 107 Hs (266) TUNGSTEN HASSIUM 106 Bh (262) TANTALUM BOHRIUM 105 Sg (145) SEABORGIUM 61 Db 144.24 DUBNIUM 60 Rf 140.91 94 EUROPIUM GADOLINIUM Nd Pm Sm Eu (237) AMERICIUM Pu Am Cm Bk NEPTUNIUM PLUTONIUM Np 93 PRASEODYMIUM NEODYMIUM PROMETHIUM SAMARIUM Pr 59 RUTHERFORDIUM (261) HAFNIUM 72 STRONTIUM Actinide Ac-Lr 89-103 104 Lanthanide La-Lu RUBIDIUM 56 137.33 132.91 Ba 55 Cs (226) BARIUM Ra 88 RADIUM (223) CAESIUM Fr 87 FRANCIUM 140.12 Ce 58 CERIUM 138.91 La 57 LANTHANIDE LANTHANUM 238.03 U 92 URANIUM 231.04 Pa 91 PROTACTINIUM 232.04 Th 90 THORIUM (227) Ac 89 ACTINIDE ACTINIUM 2 4 5 6 7 Editor: Aditya Vardhan ([email protected]) However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. Relative atomic mass is shown with five significant figures. For elements have no stable nuclides, the value enclosed in brackets indicates the mass number of the longest-lived isotope of the element. (1) Pure Appl. Chem., 73, No. 4, 667-683 (2001) PERIOD Name _______________________ Question 1 (15 points): HF Ka = 7×10-4 CuF2 Ksp = 7×10-2 [Cu(NH3)4]2+ KF = 2×1013 Rank the solubility of CuF2(s) from highest to lowest in water, 0.1 M HF, 0.1 M NH3. Concisely explain your answer, showing the reactions involved in each case. (15 points) Question 2 (25 points): Ethylenediamene (shown below) is a chelate that is typically abbreviated as “en” The formation constants, KF, of octahedral Ni2+ complex ions at 25 °C are: [Ni(en)3]2+ 2 ×1018 [Ni(NH3)6]2+ 4 ×108 a) Write the reactions for the formation and the formation constants (in terms of concentrations) for each complex ion (10 points) b) The ΔHf of the two complex ions are the same to two significant figures. How do you explain the difference in formation constants? (5 points) c) If NH3 were added to an aqueous solution of [Ni(en)3]2+ such that both concentrations were initially 1 M after mixing, what would happen? Write the reaction and discuss on which side the equilibrium would lie, and why. (5 points) d) If ethylenediamine were added to an aqueous solution of [Ni(NH3)6]2+ such that both concentrations were initially 1 M after mixing, what would happen? Again, write the reaction and discuss on which side the equilibrium would lie, and why. (5 points) Question 3 (20 points): The monomer styrene (shown below) 3 is used to make polystyrene (styrofoam). a) What is the structure of the polymer? You may answer by showing the repeat unit. (10 points) b) Show how this polymerization reaction proceeds, showing both the reactants and the products as the polymer grows. Explain concisely why this reaction proceeds over other possible reactions. (10 points) Question 4 (30 points): a) Choose three elements from a row of the periodic table and give the order you expect for increasing oxidation half-cell potential of the neutral element. Concisely explain your answer. (5 points) b) Choose two of the above and write one as a balanced oxidation half-cell reaction and the other as a balanced reduction half-cell reaction. Use realistic oxidation states. Combine the two such that the overall reaction is spontaneous as written. (10 points) c) Give the signs of ΔG° and E° that you expect for the reaction as written in b. What can you say about Keq? (10 points) d) Choose three elements from a column of the periodic table and give the order you expect for increasing oxidation half-cell potential of the neutral element. Concisely explain your answer. (5 points) Question 5 (10 points): DNA has special properties as both a polymer and the holder of our genetic code: it can be synthesized precisely, copied, and measured (sequenced). One property of a polymer (that we discussed) is rigidity. A quantitative measure of this rigidity is the “persistence length” – below the persistence length, the polymer behaves as a rigid rod; at larger scales, it behaves as a flexible chain. The persistence length of double-stranded, double-helix DNA is 50 nm. The persistence length of single-stranded DNA is ~4 nm (even lower at high salt concentration, by the way). a) Concisely explain this difference between single- and double-stranded DNA. (5 points) b) What interactions make double-stranded DNA more rigid? (5 points) Extra credit #1 (5 points): 4 In questions 2c and 2d, what would happen to the equilibria if the temperature were raised from 25 °C to 50 °C? Explain your answers. Extra credit #2 (5 points) In question 5, how might double-stranded DNA be rigidified further (chemically)? 5 Name _______________________ Section # ____ Student ID # ___________ Signature ____________________ TOTAL = ________ Chemistry 20B, Winter 2016, Sections 1 & 3, Final Exam Saturday 12 March 2016 5 questions + >1 extra credit problem, 12 pages. Answer on these sheets only. Additional space on last page. If you need extra sheets, please ask your proctor or TA. 1) Note: Only these papers can be used; no other notes are allowed. 4) Please answer each question concisely. Show your calculations. You may (and in some cases, must) draw explanatory diagrams. Label all axes and features on graphs and diagrams. 5) 2) 3) EC) You may not use a calculator, computer, watch, smart device, or electronics of any sort. Irrelevant and/or incorrect material will result in loss of points. Table of constants and conversions Speed of light: c = 3 × 108 m/s Electron charge magnitude: e = 1.6 × 10-19 C Plank's constant: ℏ = 1.1 × 10-34 J-s Gas constant: R = 0.08206 L-atm/mol-K = 8.314 J/mol-K = 1.987 cal/mol-K Boltzmann constant: kB = 1.4 × 10-23 J/K Electron rest mass: m = 9.1 × 10-31 kg Proton rest mass: M = 1.7 × 10-27 kg 1 mole = 6.02 × 1023 Faraday constant = 96500 coul/mole ΔG° = -nFE° = -2.303 RT log10Keq pH = pKa – log10 ([HA]/[A-]) You will find a periodic table for your reference on the next page. 1 1 2 3 13 5 10.811 GROUP CAS RELATIVE ATOMIC MASS (1) GROUP IUPAC ATOMIC NUMBER B 1 2 Nonmetal 16 Chalcogens element Semimetal Alkali metal 17 Halogens element Metal Alkaline earth metal - gas 58.693 - liquid VIIIB 9 10 27 58.933 28 Ne Ga 11 29 Fe Tc IB 12 30 63.546 - synthetic - solid STANDARD STATE (100 °C; 101 kPa) 18 Noble gas Lanthanide Transition metals 55.845 Actinide VIB 7 VIIB 8 25 54.938 26 51.996 65.39 IIIA 14 6 10.811 IVA 15 7 12.011 VA 16 8 14.007 VIA 17 9 15.999 VIIA 18.998 18 VIIIA 2 4.0026 He 20.180 HELIUM 10 Ne 39.948 F 18 O 35.453 N 17 C 32.065 B 16 NEON 30.974 FLUORINE 15 OXYGEN 28.086 NITROGEN 14 CARBON 26.982 BORON 54 131.29 KRYPTON Kr 83.80 Ar 126.90 36 Cl 79.904 S 53 BROMINE Br 35 P 78.96 Si 34 Al 74.922 ARGON 33 CHLORINE 72.64 SULPHUR 32 PHOSPHORUS 69.723 SILICON 31 ALUMINIUM 13 13 5 PERIODIC TABLE OF THE ELEMENTS IIA 9.0122 GROUP 2 4 http://www.ktf-split.hr/periodni/en/ 1.0079 H 6.941 SYMBOL BORON ELEMENT NAME VB 6 24 50.942 IIB IA 1 1 3 HYDROGEN Be 24.305 Li 12 BERYLLIUM 22.990 LITHIUM 11 MAGNESIUM Na Mg SODIUM IVB 5 23 Se 47.867 As IIIB 4 22 44.956 Ge 3 21 Ga 40.078 Zn 20 Cu 39.098 Ni 19 Co 127.60 Fe 52 Cr Mn 121.76 V 51 Ti 118.71 Sc 50 Xe 114.82 I 49 Te 112.41 Sb 48 Sn RADON Rn (222) At 86 ASTATINE (210) Po 85 POLONIUM (209) Bi 69 168.93 70 173.04 MENDELEVIUM 102 (259) 174.97 (262) NOBELIUM LAWRENCIUM Lr 103 LUTETIUM Lu 71 Copyright © 1998-2003 EniG. ([email protected]) BISMUTH (289) 167.26 Pb 114 Uuq 164.93 UNUNQUADIUM 67 68 Tl 162.50 LEAD 66 THALLIUM 84 In (285) MERCURY 112 UNUNBIUM 158.93 (258) YTTERBIUM Er Tm Yb 101 THULIUM ERBIUM (257) FERMIUM Fm Md No 100 Ho (252) HOLMIUM 99 Dy (251) Es BERKELIUM CALIFORNIUM EINSTEINIUM Cf 98 DYSPROSIUM (247) Tb 97 TERBIUM 65 208.98 Cd (272) 157.25 (247) 83 Ag 64 Gd 96 207.2 Pd 151.96 (243) 82 Rh 63 95 204.38 XENON 150.36 (244) CURIUM 81 IODINE 200.59 TELLURIUM 80 ANTIMONY 196.97 TIN 111 GOLD Au Hg 79 INDIUM 195.08 CADMIUM 78 SILVER 192.22 PALLADIUM 77 RHODIUM 107.87 Ca 190.23 47 K 76 106.42 SELENIUM 186.21 46 ARSENIC 75 102.91 GERMANIUM 183.84 45 GALLIUM 101.07 Ru 44 ZINC (98) Tc 43 COPPER 95.94 NICKEL 42 COBALT 92.906 74 MOLYBDENUM TECHNETIUM RUTHENIUM Pt 180.95 Ir 73 NIOBIUM Nb Mo 41 IRON 91.224 CHROMIUM MANGANESE 40 VANADIUM 88.906 TITANIUM 39 SCANDIUM 87.62 CALCIUM Zr 38 Y 85.468 POTASSIUM Sr 37 Rb ZIRCONIUM Os 178.49 57-71 YTTRIUM Re (281) W 110 Ta (268) Hf 62 MEITNERIUM UNUNNILIUM UNUNUNIUM Mt Uun Uuu Uub 109 PLATINUM (277) IRIDIUM 108 OSMIUM (264) RHENIUM 107 Hs (266) TUNGSTEN HASSIUM 106 Bh (262) TANTALUM BOHRIUM 105 Sg (145) SEABORGIUM 61 Db 144.24 DUBNIUM 60 Rf 140.91 94 EUROPIUM GADOLINIUM Nd Pm Sm Eu (237) AMERICIUM Pu Am Cm Bk NEPTUNIUM PLUTONIUM Np 93 PRASEODYMIUM NEODYMIUM PROMETHIUM SAMARIUM Pr 59 RUTHERFORDIUM (261) HAFNIUM 72 137.33 56 STRONTIUM 132.91 Actinide Ac-Lr 89-103 104 Lanthanide La-Lu RUBIDIUM Ba 55 Cs (226) BARIUM Ra 88 RADIUM (223) CAESIUM Fr 87 FRANCIUM 140.12 Ce 58 CERIUM 138.91 La 57 LANTHANIDE LANTHANUM 238.03 U 92 URANIUM 231.04 Pa 91 PROTACTINIUM 232.04 Th 90 THORIUM (227) Ac 89 ACTINIDE ACTINIUM 2 4 5 6 7 Editor: Aditya Vardhan ([email protected]) However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. Relative atomic mass is shown with five significant figures. For elements have no stable nuclides, the value enclosed in brackets indicates the mass number of the longest-lived isotope of the element. (1) Pure Appl. Chem., 73, No. 4, 667-683 (2001) PERIOD Question 1 (15 points): Can an infrared photon break a typical covalent bond? Why or why not? (15 points) Question 2 (25 points): For the reaction of Si(s) + O2(g) → SiO2(s) a) What are the signs of ΔH, ΔS, and ΔG? Explain each of your answers concisely. (15 points) [Hint: what would C do, in place of Si?] b) Petrified wood comes from dehydration (loss of water) of silicic acid, Si(OH)4 (shown below), ultimately to form quartz, SiO2 (after the silicic acid has replaced the organic matter in the plant; the colors from metal ions that are left in the quartz crystals). Show the first step in the polymerization reaction, starting with the reaction of two silicic acid molecules, including showing the reaction products. (10 points) Question 3 (10 points): Recall from the third midterm that the monomer styrene (left) is used to make polystyrene (middle), the main component of Styrofoam. Last Wednesday, at the International Conference on Nanostructures on Kish Island, Iran, in the talk before mine, Prof. Luis Liz-Marzán (right, one of the world’s leading nanoscientists, the director of the nanocenter CIC biomaGUNE, San Sebastian, Spain, who has been knighted by the King of Spain) showed that he could make crystalline lattices of Au nanoparticles that were coated with polystyrene. In each of the three electron microscope images below, all the 18-nm Au nanoparticles (which appear as spots) are the same, other than their polystyrene coating. Each polystyrene chain is chemically attached to the 18-nm Au nanoparticle at one end, so each particle has the same number of attached chains. The only difference from top to bottom in the images is the molecular weight (MW) of the polymer chains: 5800, 21,500 and 53,000 amu. Each spot in the electron microscopy image is an 18-nm Au 3 nanoparticle within a small crystal of nanoparticles; the polymer surrounding each nanoparticle is not observed (because C and H do not interact with electrons as strongly as Au does). a) Why are the Au nanoparticle spacings different and in this order, in terms of the attached polymer molecular weight? (Ignore the points in the plot for the different sizes of nanoparticles.) (5 points) b) Estimate the average polymer chain lengths in each case in terms of number of monomer units. Recall that each carbon has four bonds and the H atoms are not shown in the molecular structures above. Show your work. (5 points) 4 Question 4 (20 points, extra points are possible): Fluorescence is a widely used quantitative method of detection. For example, in flow cytometry, two different dyes can be used and separately interrogated to label DNA in terms of the total amount of C-G vs A-T content in individual chromosomes. This is shown schematically below. a) Explain concisely how we can tell the two dyes apart. (10 points, + bonus points if you correctly draw, use, and explain energy level diagrams for both ) b) Explain concisely how we can tell how much of each type of base pair (C-G and A-T) and dye is present. (5 points) c) If a piece of a chromosome is missing, what happens to the two signals? (5 points) Question 5 (30 points): The half-life of 14C is approximately 5700 years. The ratio of 14C/12C in the atmosphere is approximately 1.2×10-12. If a tree was seeded and started to grow 17,100 (=3×5700) years ago and lived for 5700 years (ok, I know that is a long life for a tree, but nobody was carving their initials in it): a) Draw and concisely explain a plot of the 14C/12C ratio in the tree for the last 17,100 years. (15 points) b) For the first 5700 years since the tree was seeded and started to grow and for the time since, give the functional form of the plot. (5 points) c) What is the reaction order in [14C] for the 11,400 years since the tree died? Explain concisely. (5 points) d) What is the 14C/12C ratio in the (dead) tree now? Show your calculation. (5 points) Extra credit #1 (10 points): For question 2a, write balanced half-cell redox reactions that could be used to measure the Ecell and ΔG for this reaction. Label the oxidation and reduction half-cell reactions. 5