Significant Figures



Significant FiguresRuler A – 4.40 cmRuler B – 4.4 cmAdd 1 more decimal than the smallest measurement can measure.Type of 0Significant?0.00003placeholderno3,0000placeholderno3,0003trappedyes3.0000preciseyes Adding sig figs – do not count the # of sig figs! Count the # of decimal places.% error = I valueacc - valueexpI x 100% valueaccmicro? 106 ?m = 1 mnanon 109 nm = 1 mpicop 1012pm = 1 mSubstanceDensityLiq. Water1.00 g/mLGas at STPmass of 1 mol/22.4LAverage atomic mass = % x mass + % x mass +….. (isotope 1)(isotope 2)1 mole = 6.022 x 1023 particles. (Avogadro's number)1 12C atom = 12.00 amu (atomic mass)1 mole 12C atom = 12.00 g (molar mass)A = mass number Z = atomic numberA = number of protons + neutronsZ = number of protonsA – Z = # of neutronsIsotopes= atoms with same number of protons but different numbers of neutronsIons= electrons varyIsomer – different arrangements if atoms within a moleculesPROTONS, Atomic # define the element!NameFormulamethaneCH4ethaneC2H6propaneC3H8butaneC4H10pentaneC5H12hexaneC6H14heptaneC7H16octaneC8H18nonaneC9H20decaneC10H22….eneCnH2n…yneCnH2n-2Covalent prefixesNumberPrefixNumberPrefix1mono-6hexa-2di-7hepta-3tri-8octa-4tetra-9nona-5penta-10deca-MnO4-permanganateS2O3-2thiosulfateCrO4-2chromateCr2O7-2dichromateO2-2peroxideClO-hypochloriteClO2-chloriteClO3-chlorateClO4-perchlorateC2O4-2oxalateFe(CN)6-4 hexacyanoferrate(II)/ ferrocyanideFe(CN)6-3 hexacyanoferrate(III)/ ferricyanideBO3-3borateHg2+2 mercury (I) ionMolecular formula = the way a molecule really appears in natureEmpirical formula = smallest whole number ratio of elements QUOTE = QUOTE = whole number always! Glucose has a molecular formula (MF) of C6H12O6Glucose’s empirical formula (EF) is CH2OGlucose’s molar mass (MM) is 180 g/molGlucose’s empirical mass (EM) is 30 g/molEF X 6 = MF; EM X 6 = MM for glucose!Solving EF problems:1. If given percentage, drop % and use g. (assume 100 g)2. if given mass, just leave it!3. Convert g of each element to moles to get mole ratio.4. Divide by smallest to get lowest whole number ratio.5. if dividing by smallest does not give whole number ratio, then multiply all by a whole number:.2,.4,.6,.8 x 5.25, .75 x 4.33, .67 x 3Diatomic molecules - Br?NClHOFOther Molecular ElementsPhosphorus--one form P4Sulfur—often S8Carbon--4 allotropes, diamond and graphite, buckyballs, graphene, all covalent networksOther compounds to memorize1. Hydrogen Peroxide – H2O22. Ammonia – NH3REACTIONS TO MEMORIZE:1. Synthesis reactions of metal oxides with water: .ex: Na2O + H2O 2NaOHCaO +H2O Ca(OH)22.Synthesis reactions of nonmetal oxides with water: ex: SO3 + H2O H2SO4N2O5 + H2O 2HNO33.Decomposition of Binary Compounds ex: 2H2O 2H2 + O2MgS Mg + SH2O2 H2O + O24.Decomposition of Metal Carbonates: ex: CaCO3 CaO + CO2Na2CO3 Na2O + CO25.Decomposition of Metal Hydroxides: ex: Ca(OH)2 CaO + H2O2NaOH Na2O + H2O6.Decomposition of Metal Chlorates: ex: 2KClO3 2KCl + 3O2Mg(ClO3)2 MgCl2 + 3O27.Decomposition of Metal Nitrates: ex: 2NaNO3 2NaNO2 + O2Ba(NO3)2 Ba(NO2)2 + O28.Decomposition of acids: certain acids can decompose to form nonmetal oxides and water.ex: H2CO3 CO2 + H2OH2SO3 SO2 + bustion: elements in a compound separate and combine with oxygen to make most reasonable cmpds.ex: ABC + O2 AO + BO + CO2 C2H5OH + 3 O2 2 CO2 + 3 H2O CS2 + 3 O2 CO2 + 2SO210. Single Replacement: A metal replaces a metal or a nonmetal replaces a nonmetal IF the element doing the replacing is higher on the activity series. Hydrogen replaces/is replaced by metals, though.Ex: MgCl2 + 2Na 2 NaCl + Mg Cl2 + 2 NaI 2 NaCl + I2 2 HCl + Mg MgCl2 + H211. Double replacement: Only works if 1 of following is produced: 1. Precipitate 2. Gas 3. WaterIf the following is madeIt decomposes into…NH4OHH2O + NH3H2SO3H2O + SO2H2CO3H2O + CO2All compounds containing group 1 metals, acetates, nitrates, or ammonium are soluble. BaSO4, PbI2, and AgCl are common insoluble substances!There is no such thing as an oxide ion in solution! It will quickly become a hydroxide ion!Preparing Solutions:1. Always use volumetric flask.2. Add solute or concentrated solution.3. Fill to the line with deionized water.4. Shake.McVc = MdVdMc = molarity of concentrated solution (used to make new soln)Vc = molarity of concentrated solution (used to make new soln)Md = concentration of solution producedVd = volume of solution produced = vol. of concentrated soln + volume of water!Leo says Ger!!!!Losing Electrons is OxidationGaining Electrons is Reduction!EX: 2 AgNO3 + Zn Zn(NO3)2 + 2 Ag 2 Ag+ + Zn Zn+2 + 2 Ag Silver is reduced; zinc is oxidized2 moles of electrons are transferred (not 4!) Half reactions: 2 Ag+ + 2 e- 2 Ag Zn Zn+2 + 2e-Half reactions are often easy!If not single replacement, use….All Oranges Have Citrus Energy!1. Separate into half reactions. Leave out spectators.2. A = balance atoms (except H and O)3. O = balance oxygens (add H2O for acid rxns; add 2 x OH- for bases) 4. H = balance hydrogens (add H+ for acid rxns; add H2O for bases) 5. C = balance charge (by adding electrons) 6. E = balance electrons (by multiplying half reactions)Assigning Oxidation Numbers:In free elements, each atom has an oxidation number of 0.For ions consisting of a single atom, the oxidation number is equal to the charge on the ion.For binary ionic compounds, assign oxidation numbers (charges) as you always have!For covalent molecules, or polyatomic ions, assign oxidation numbers in the order shown below.F-O-H, closest to F, farthest from FFluorine is always assigned first an oxidation number of –1 when in a compound.Next, assign oxygen. The oxidation number of oxygen is -2 in most compounds.Exceptions: Oxygen in peroxides is -1 Ex. H2O2 Na2O2Then, assign hydrogen. The oxidation number of hydrogen is usually +1, but may be –1 when combined with a metal. For example: H in hydrides is -1 Ex. NaHFor compounds in which both atoms cannot have the oxidation number which is equal to the charge the element commonly has, one closest to fluorine “wins”. HEATTotal amount of kinetic energy of a sampleqJoulesTEMPERATUREA measure of average kinetic energy of a sampleToC, KSPECIFIC HEATThe amount of energy required to change the temp of 1 g of substance by 1oCCJ/goCcal/goCJ/moloCHEAT CAPACITYThe amount of energy required to change the temp of a given substance by 1oCnoneJ/oCcal/oC1 mL H2O = 1 g H2O Enthalpy = heatAmount of energy to change temp of 1oC of H2O = 1 cal4.184 J = 1 cal 1000 cal = 1 kcal = 1 Cal200 g water at 70oC100 g water at 70oCSame TSame KEavg of particlesSame speed of particlesSame specific heat of waterMore heat energy (q)Less heat energy (q)Heat of formation?HfEnergy required to form an element from its standard stateHeat of fusion?HfusEnergy required to melt a substance or RELEASED when frozenHeat of vaporization?HvapEnergy required to boil a substance or RELEASED when condensedHeat of reaction?HrxnEnergy required/released during a reaction (per mole)Heat of combustion?HcombEnergy required/released during a comb. reaction (per mole)Ionization energyIEEnergy required to remove 1 electron from an atomLattice EnergyUEnergy required to break 1 mole of ions in a crystal lattice into gaseous ionsStandard entropy?SMeasure of disorder compared to that of a solid crystal at 0KGibbs Free Energy of formation?GfMeasure of spontaneity; ability to do work on surroundings as compared to elements in standard stateGibbs free energy of reaction?GrxnMeasure of spontaneity; ability to do work on surroundingsWays to Calculate the Enthalpy of reaction, ?Hrxn:1. ?Hf (products) - ?Hf (reactants)2. bonds broken – bonds made3. sum of ?Hrxn for reactions that add up to new reaction4. measure amount of energy gained/lost by water. Divide by moles of 1 reactant reacted.PersonExperimentDiscovered/ProposedDalton-Atomic Theory – 5 postulates, incorrect about all atoms of a given element identical and atoms are indivisibleMendeleevDesigned Periodic Table; left holes for 3 missing elements and predicted their propertiesThomsonCathode raysAll matter contains electrons (and therefore protons); determined mass:charge of electron; Proposed plum pudding model of atom (p+/e- spread throughout)MillikanOil drop experimentDetermined exact mass and charge of electronRutherfordGold foil experimentDiscovered positively charged, very dense nucleusEinsteinPhotoelectric EffectphotonsPlanck-Calculated “size” of photon – Planck’s constantBohrLine emission spectrum of (excited) hydrogen gasExistence of energy levels/ quantized energy states of electronsDe Broglie-De Broglie equation; wavelength of any moving objectSchrodinger-Schrodinger’s equation; calculates probability of finding electron in a given region (orbital!) within an atom by treating electron as probability wave functionHeisenberg-Uncertainty Principle; the greater the precision in measuring a small object’s location, the greater the uncertainty in measuring its velocity and vice versa (can’t know an electron’s location and velocity simultaneously)Excited electrons have gained energy and jumped to a higher energy level. They possess more energy.They fall back down to a lower energy state and must release energy in the form of 1 quantum/photon, E = hνOnly certain sized photons (lines of frequency/wavelength) are emitted so each element has its own distinct line emission spectrum. This is due to the existence of quantized energy states in atoms.Pauli Exclusion PrincipleNo 2 electrons in the same atom can have the same 4 quantum numbers; thus no 2 electrons can be in the same energy level/sublevel/orbital AND have same spin; 2 electrons in same orbital must have opposite spinsAufbau RuleElectrons fill up orbitals from lowest energy to highest energy (this may not be in numerical order! See aufbau box below) 2 is higher than 1; d is higher than p, etc….Hund’s Rule (Bus Rule!)If 2 equal energy orbitals are available, electrons each go to separate orbitals (with same spin) before pairing up 2p: ____ _____ _____Sublevelorbitals withinShape of orbitalsPicture# of electrons in an orbital# of electrons in sublevelssSpherical22ppx, py, pzDumbbell shaped26ddxy, dxz, dyz, dz2, dx2 –y24 lobed210f7 different f’s8 lobed/too complexDon’t even try214g9 different g’s!!!!!AAAAH!218Quantum numbers describe where a given electron is in an atom. 1st quantum #Energy level1, 2, 3, 4….2nd quantum #sublevels, p, d, f3rd quantum #Orbital/orientationpx, py, pz,for example4th quantum #spinWhich one has higher Coulombic attraction? Why?Aufbau box: (add arrows)1s2s 2p3s3p3d4s4p4d4f5s5p5d5f5g6s6p6d6f6g6h7s7p7d7f7g7h7i8s8p8d…….Example of orbital notation:C: ____ ____ _____ _____ ______ 1s 2s 2pExamples of electron configuration:Mg: (you do it!)K: 1s22s22p63s23p64s1Mn: 1s22s22p63s23p64s23d5Ag: 1s22s22p63s23p64s23d104p65s14d10Pb: (you do it!)# unpaired electrons = #electrons alone in orbitalC has 2 unpaired electronsK has 1, Ag has 1, Pb has 2, Mn has 5, Mg has 0Unpaired electrons make element paramagnetic.Drawing Lewis Structures for COVALENT compounds: The atom with lowest EN is the central atom.Count the total number of valence electrons. MAGIC NUMBER! (adjust for ions)Place one sigma bond (a pair of electrons) between each pair of bonded atoms.Subtract the total number of valence electrons used for bonds from the MAGIC NUMBER. Place lone pairs about each terminal atom except for hydrogen atoms. Subtract the number of lone pairs from the sum.If e- are still left at this point, assign them to the central atom. If the central atom is from the third or a higher period, it can accommodate more than four pairs of electrons.If the central atom is not yet surrounded by four electron pairs, convert one or more terminal atom lone pairs to pi bond pairs.IONICCOVALENTMetal + nonmetalMetal +polyatomic ionPoly ion + nonmetalPoly ion + poly ionNonmetal + nonmetalWithin poly ionStrongest type of bondWeaker bondElectrostatic attraction between oppositely charged ionsElectrostatic attraction between nuclei and shared electronsElectrons transferred, creating ionsElectrons shared – NO IONS!Forms crystal latticeAnd thuscrystalsA few form covalent networks (SiO2, , most form individual moleculesFormula unitsmoleculesHigher MP, Higher BP(must break bond to change phase)Lower MP, lower BP(only break IMFS NOT bonds to change phase)Lattice EnergyBond energyHigher charge, smaller size= stronger bondHigher bond order, smaller atom = stronger bondForms polar and nonpolar bondsLarge EN differenceMedium (polar) or Small (nonpolar) EN differenceIf soluble, forms electrolytes when dissolvedNonelectrolytes, may dissolve but won’t ionize!Electrolytic when molten, not solidNonelectrolyteHigh % ionic characterLow % ionic characterShow resonance!Total number of sigma bonds and lone pairs on central atomShapeAtoms bonded to central atom(# of sigma bonds)Lone pairs on central atomMolecular Shape PictureAnd bond anglesHybridizationSymmetrical in 3d space?Example of a Lewis structure that is this shape. (Yes, draw the Lewis structure!)2Linear20spyes3Triangular Planar30sp2yes3Bent21sp2no4Tetrahedral40sp3yes4Triangular pyramidal31sp3no4Bent22sp3no5Trigonal bipyramidal50dsp3 or sp3dyes5Unsymmetrical tetrahedron(see saw)41dsp3 sp3dno5T-shaped32dsp3 sp3dno5Linear23dsp3 sp3dyes6Octahedral60d2sp3 sp3d2yes6Square pyramidal51d2sp3 sp3d2no6Square planar42d2sp3 sp3d2yesTYPEUSESTO DETERMINE/ProduceHOWMass SpectroscopyMagnetsDistinguishes isotopes (separates by mass), can be used to determine % abundance of each isotopeThe magnet bends heavier isotopes more than lighter onesPhotoelectron SpectroscopyBeam of Light on MetalBinding Energy of electrons in different sublevels within a given atom“Light” beam (could be other form of ER) gives energy to electrons and removes them from the atom- this energy is measured…takes more energy to remove innermost electrons than outermost electronsAtomic absorption spectroscopy or Atomic Emission SpectroscopyElectrical or Heat Energy added to excite electronsLine Emission spectrum (or line absorption spectrum) which identifies the elementEnergy excites electrons and they absorb a specific wavelength, then when they fall back down, they release a specific wavelengthNMR Spectroscopy (nuclear magnetic resonance)Radio waves (LOW Energy right?) added to “excite” nucleusIdentity of a substance (types of atoms present)Nucleus vibrational states altered by radio waves, gives “signature” of elementInfrared or Visible or UV spectroscopy (example: Using spectroscopes)IR or Visible light or UV light to excite electrons in bondsIdentity of a substance/molecule, (types of bonds present) OR concentration of substance (when we used spectrophotometer)Electrons in bonds also have quantized energies and these energies can be used to identify a moleculeMass Spectrometry Data: …each bar represents the mass and abundance of a given isotope. What element? _______PES data: (photoelectron spectroscopy)…each bar represents the abundance AND energy to remove each of the electrons from an atom (binding energy!). The outermost electrons take the least amount of energy to remove.2s2p1s3s When bond is formed, 2 atoms rest at a distance of minimum potential energy. This gives the typical bond length of the molecule.----------------------------------------------------------?E = q + w?E = internal energyq = heat added to the systemw = work done on the systemSo, for example if heat is added to the system AND work is done on the system, then the internal energy of the system increases and has a positive sign.If a reaction is exothermic and it expands in volume, work is done on the surroundings and so work is negative, and heat is negative, and the internal energy decreases and change in energy has a negative sign.---------------------------------------------------------During phase change, added or removed heat doesn’t change kinetic energy of particles and thus, does not change the temp. Energy is used to break IMFs or released when formed.Boiling point – temp at which v.p equals atmospheric pressure.Normal b.p. –temp at which v.p equals 1 of hump = activation complex/transition state/high-energy intermediateTaller the “hump”, slower the reactionActivation energy is used to break bonds, create an “effective” collisionEffective collision:1. enough energy to react/break bonds2. correct orientationA 2 step mechanism might result in double hump.Slow step only determines rate of reaction. (slow step has higher hump)Activation energy with catalyst5 factors that affect rate of reaction: 1. nature of reactants2. concentration: increases # of collisions3. phase/ surface area: increases # of collisions4. temperature: increases # of collisions AND # of effective collisions5. catalyst: Increases # of effective collisions by lowering activation energyConsider this reaction: A+ B D+ E Rate = k [A]x[B]y[C]z NOT to be confused with equilibrium expression: K = QUOTE Exponents (in rate law) are NOT determined by balanced equation.Exponents can match slow step of mechanism.Exponents can only be determined experimentally.k depends on T.A catalyst can be included (C perhaps)Products are (almost) never included – no denominator (in most cases)How is rate law determined experimentally?Method of Initial Rates: Start with different concentrations of reactants and measure initial rate.If tripling A causes rate to increase 9-fold, exponent of A is 2.Measure the concentration over time. Make a graph to see what order.1 mol gas at STP = 22.4 L2 ways a gas may not be ideal:Large sizePolarAn unideal gas:Tends to have inelastic collisions, and/orHave a size that DOES matter AND doesn’t obey the gas laws perfectly.Any gas is more real (unideal) atHigh pressure (size of particles does matter)Low temperature (particles more likely to have inelastic collisions)Any gas is more ideal atLow pressureHigh temperature 2 balloons each filled with different gases at the same volume in the same room.CO2HeSame V, T, and PSame KE.Same number of gaseous particlesHigher mass, higher densityLower mass, lower densityLower speed of particlesHigher speed of particlesZero Order1st order2nd orderRate lawRate = kRate = k[A]Rate = k[A]2Rate depends on [A]NO!YesYesIntegrated Rate law[A] = -kt + [A]oln [A] = -kt + ln [A]o1 = kt + 1[A] [A]oPlot needed to give a straight line[A] vs. tln [A] vs. t1/[A] vs. tRelationship of rate constant to slope of straight lineSlope = -kSlope = -kSlope = kHalf lifet1/2 = [A]o/2kt1/2 = 0.693/kt1/2 = 1/k[A]oHalf life depends on [A]yesNO!yesWhat are IMFs?NOT bondsAttractions between neighboring speciesMUCH Weaker than bonds usuallyIncreasing vapor pressure, volatility, likelihood of being gas at room tempThe 5 types of intermolecular forces (IMFS) listed from strongest to weakest are:Ion-ion (NOT really an IMF)Example: Salt bondsIncreasing m.p., b.p , Hfus, Hvap, critical point, specific heatIon-dipoleExample: Salt dissolving in water Dipole-dipole (Strongest type is hydrogen bonding)Example: Water condensingDipole-induced dipoleExample: CO2 dissolving in waterInduced dipole-induced dipole AKA London dispersion forcesAKA Van der Waals forces Example: freezing nitrogenThe stronger the IMFS, the lower v.p. at given T.The stronger the IMFs, the higher the normal b.p.Types of crystalline solids:Ionic –formed from ionic bonds, very strong, brittle, high MP, think NaClMolecular – formed from the regular arrangement of IMFS between covalent molecules, low MP, not strong, think snowflakesNetwork – covalent bonds throughout, high MP, hard, nonconducting (usually), think SiO2 (sand/glass), C (diamond)Graphite is a unique network solid made only of carbon atoms. They are bonded together in sheets. The sheets are attracted to each other by weak IMFS. (rubs off easily) Within the sheets, there is resonance throughout, allowing graphite (a nonmetal) to conduct electricity!Ways to increase solubility of aSolidgasIncrease tempDecrease tempIncrease surface areaIncrease pressure aboveAgitation, stirringDon’t agitateΔHsoln (heat of solution): SUM OFEnergy required to break the water-water IMFsEnergy required to break IMFS in soluteEnergy released when IMFS form between solute and solvent.Hydrogen bond: the ATTRACTION between a H of one molecule (that is bonded to a very EN element such as F, O, N) and a very EN element (O, F, N) of another molecule. NOT A BOND!!!!!!!!!Ways to measure the concentration of a solution:Molarity (M) = mol solute/L solutionMolality (m) = mol solute/kg solventMole fraction (X) = mol solute/ mol solution% by mass = g solute/g solution% by volume = mL solute/mL solutionm/v % = g solute/mL solutionColligative property: any property of a solution that changes based SOLELY on the NUMBER of solute particles dissolved. (not mass or size or IMF formed!)-freezing point depression-Vapor pressure lowering-Boiling point elevation (as a result of v.p. lowering!)WHY? Solute particles interfere with the process of evaporating, boiling, and freezing.Alloys are metal solutions. (homogeneous mixtures)Substitutional alloy: formed by 2 metals of similar radii; mp or ability to resist corrosion or conductivity might be affected. Hardness is NOT.Interstitial alloy: formed by 2 metals of different radii; adding in smaller metals tend to make the alloy harder.For both alloys, adding metals with more valence electrons increases conductivity.Strong acid:Weak acid:Strong base:Weak base:Soluble ionic compound:Insoluble ionic compound:Soluble covalent compound:Insoluble covalent compound: Force of attractionDO NOT MIX CONCEPTS! Periodic trends do NOT explain boiling point for example. WHY …?ONLY Reasons you will useDoes X have a larger radius than Y? a higher ionization energy than Y? a higher electronegativity than Y? a higher reactivity than Y?Tell how many protons and electrons each species hasThen, use proton-electron attraction (Coulomb’s LAW)OR electron-electron repulsion (Coulomb’s LAW)OR shielding (electrons don’t feel protons pulling on them due to intervening energy levels)Does Y make a given shape? Have a given bond angle?VSEPR THEORY!!! Bonding pairs of electrons experience repulsion with each other so they spread out in 3d space as far as possible; Lone pair electrons induce greater repulsion and cause angles between bonding electrons to be smaller than expected.Is Y polar?Electronegativity difference (polar or nonpolar bonds?) AND Symmetrical or Unsymmetrical shapeDoes Y dissolve in Z? Have a high freezing pt, low volatility, low vp, high critical pt, high melting pt, high Hfus, high Hvap?Identify intermolecular force involvedCompare strengths of intermolecular forceDoes SOLUTION A Have a high b.p., high conductivity, low f.p., low v.p?Compare [ ] of solutions Ksp problem types: always AB A+ + B-1. Calculate solubility using Ksp: Do RICE solve for x2. Calculate Ksp using solubility: Do RICE, solve for K3. Calculate solubility within a solution of common ion: Do RICE, solve for X (should not have all 0’s on I row)4. Calculate if precipitate forms when mix 2 solutions:- MV = MV to determine new concentration- Plug into equil expression to get Q- Compare to K5. Calculate how much of a given substance is required to form precipitate, (or compare which precip forms 1st)- Solve equil expression for missing value!Le Chatelier’s principle:If a reaction is stressed, the reaction responds in such a way as to remove that stress. Equilibrium can be disturbed by:Adding products (shifts left)Adding reactants (shifts right)Removing reactants (shifts left)Removing products (shifts right)Adding volume or decreasing partial pressure (shifts towards side with fewer gaseous or aqueous particles)Increasing temperature (shifts to get to new K)Shifts right if endothermicShifts left if exothermicEquilibrium canNOT be disturbed by:Adding inert gas (no effect)Adding solid (no effect)The ONLY way to change K is to change the temperatureK >1 products preferred at equilibriumBuffer: combination of (weak) conj. acid/base pair that resists change in pHA good buffer:1. desired pH = pKa of acid2. [conj. acid] = [conj. base]3. [conj.acid] and [conj. base] high (increases buffering capacity)How to approach ANY titration calculation:Molarity x volume = moles for both substances.Subtract to see what remains. Does a conjugate acid or base get produced? (it will in any weak titration.) Determine its moles.Divide by volume to get molarity for substance remaining.THINK….how do I get pH of this/these substances?–log [strong]If weak, RICEIf weak acid and weak base are present, do H-Hasselbach.At equivalence point of ANY titration: MaVa = MbVb, moles acid – moles base = 0Midpoint = half moles neutralized (AND [weak acid/base] = [conj. acid/base]); pH = pKaTitrationsStrong acid/strong baseStrong acid/weak baseStrong base/ Strong acidStrong base/weak acidStarting pointhighnot as highlownot as lowMidpointNot relevantpH= pKaNot relevantpH = pKaEquivalence pointExactly 7Below 7 (conjugate acid present)Exactly 7Above 7(conjugate base present)Vertical regionVery longNot as longVery longNot as long Always pick an indicator whose pKa = pH at the equivalence point of the titration.Various Ways to Describe Acid StrengthPropertyStrong AcidWeak AcidKa ValueToo large to measure<< 1Position of the dissociation equilibriumrightleftEquilibrium concentration of H+ compared to the original concentration of HA[H+ ] = [HA]o[H+ ] << [HA]oEquilibrium concentration of HA compared to the original concentration of HA[HA] ~ 0 M[HA] << [HA]o[HA] ~ [HA]oPercent Dissociation100%< 5%Strength of conjugate base Conjugate base is nonexistentConjugate base is also weak, but inversely proportional in strength to the acid (Kb = Kw/Ka).How to represent in a net ionic equationH+ + A-HASignOf H0System Entropy ChangeSignofS0Sign of G0Sign of E0(if a redox)KSpontaneous? (Thermodynamically favorable?)1. Exothermic-Increasing+-+>1always2. Exothermic-Decreasing-+ or -- or +Don’t knowLow T3. Endothermic+Increasing++ or -- or +Don’t knowHigh T4. Endothermic+decreasing-+-< 1neverGalvanic Cell/ Voltaic Cell/ Electrochemical CellSpontaneousEx: battery!Chemical energy electrical energyE = +ΔG = -anode= oxidationCathode = reductionElectrolytic CellNonspontaneousEx: electrolysis waterElectrical energy chemical energyE = -ΔG = +Anode= oxidationCathode= reductionAs reaction progresses, K doesn’t change BUTWhen rxn is shifting rightWhen rxn is shifting leftWhen a reaction is at equilibriumQ approaches KQ < KQ > KQ = KG approaches 0G = - G = +G = 0E approaches 0 E = +E = -E = 0+1H+1/-1+2Increasing nuclear charge explains everything: increasing ability to attract electrons, decreasing AR, increasing EN, increasing IE, which both explain decreasing reactivity across metals, increasing reactivity among nonmetals-4-3-2-1No ions formed usuallyHighest IES blockMost reactive nonmetal, highest ENNo measurable EN (too low), high IE, INERT!Alkali ne earth metals+3p blockAlkali metals Zn+2(+2) +4d block (1 behind!)Transition metalsAg+1Cd+2 roman numeral Sn Sb57-70*Variable positive charge = roman numeral PbRoman numeral(+3) +5+6Most reactive metal, lowest IE, lowest EN89-102**+7Increasing # of energy levels (increased shielding) explains everything:Decreasing ability to attract electrons, Increasing AR, Decreasing IE, Decreasing ENWhich explain increasing reactivity among metals, decreasing reactivity among nonmetals*Lanthanide series, 4fVariable positive charge = roman numeralRare earth metals**Actinide series, 5f 57-70* 89-102*****Page 16: Look on the internet for an interesting molecule that has many atoms. Draw its Lewis structure below and 1. Give its molar mass, 2. Give its mass per molecule. Then pick 2 central atoms that have different hybridizations and label their 3. Hybridization, 4. Bond angles, 5. Shape about that atom A good website to try might be (Molecule of the Month).Which atom?1. 2.3.4.5.Which atom?3.4.5. ................
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