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by: Josie O'Shea

GenChemUnitExam2.pdf CHEM 127

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Josie O'Shea

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Chapters 11&12 notes
General Chemistry I
Study Guide
General Chemistry
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This 6 page Study Guide was uploaded by Josie O'Shea on Thursday February 11, 2016. The Study Guide belongs to CHEM 127 at Oregon State University taught by in Winter 2016. Since its upload, it has received 28 views. For similar materials see General Chemistry I in Chemistry at Oregon State University.

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Date Created: 02/11/16
Monday, February 8, 2016 General Chemistry Unit 2 Exam Chapters 11 & 12 Chapter 11( Intermolecular Forces): Dispersion (London) Forces: temporary polarity (melting point: -219C, ex: O2) - occur in all • substances • Dipole-Dipole attractions: polar molecules have a permanent dipole; attraction between opposing charged regions leasts to attractive force in addition to induced dipole(melting point: -95C, ex: CH3CHOCH3) • Ion-Dipole attraction: (stronger than H bond) driving force of solution of ionic compound - ions attracted to the dipole of polar molecules • Cation-Anion attraction: Coulomb’s law: F= ((q+)(q-))/(r2) - larger q : larger attraction ; shorter bond length(r) : stronger attraction • H- Bonding: (stronger than dipole-dipole )hydrogen atom covalently bonded to N, O, or F in one molecule (being partially positively charged) forms a 1+ bond w/ N, O, or F (melting point: 0C) • Ionic Bonding: melting point:801C, ex: NaCl • Network Covalent Bonding: melting point:3550C, ex: Diamond • Larger molar mass: stronger dispersion force • Strong attractive forces: high melting & boiling points; weak attractive forces: low melting & boiling points • larger atoms have outer electrons further from nucleus —> more polarizable • Polarizability: ratio of the induced dipole moment of an atom to the electric field that produces this dipole moment. • Network Covalent Solids: Quartz (SiO2), graphite, diamond, silicon, BN, SiC ; Diamond - melting point: 3550C - network of sp3 bonds; graphite: melting point:3880C - layered structure - sp2 bonda in plane, Van dre Waal force between planes • Metals: metallic bond also very strong Crystalline Solids • molecular crystal: low mp, assembled by Van der Waals force between molecules • Ionic Crystal: high mp, assembled by ionic bonding all through solids - not always metal/ nonmetal (ex: NaCl, MgO) • Metallic Crystal: metallis bond; variable mp: Hg, -38.83C to W3422C 1 Monday, February 8, 2016 • meniscus/capillary action: competition between adhesive and cohesive forces produce a curved meniscus (H20 - glass: adhesive stronger) • Capillary action: adhesive forces pull a liquid up a narrow tube against gravity (Hg-glass<Hg- Hg, cohesive stronger) • Surface Tension: minimize the surface to maximize the liquid-liquid interaction Vaporization Vaporization: molecules w// enough KE overcome attractive forces and escape from liquid • surface to become gas: vapor — endothermic (as T increases, the fraction of molecules w/ “escaping energy” increases) • Volatile: liquids w/ weak intermolecular forces Condensation (reverse vaporization) • condensation: vapor molecules turns into liquid: exothermic, releasee energy When Condensation & Vaporization Equilibrate • when rate of evaporation = rate of condensation : the partial pressure of the vapor in the air is its Vapor Pressure(VP) • High VP: Weak Intermolecular Forces • Boiling Point: the temperature at which VP= external P(air pressure) • normal boiling point: temperature @ which VP=1 atm Melting(Fusion) & Freezing • at melting point, molecules in a solid have sufficient KE to overcome some of the attraction that holds them in position & the solid melts • Sublimation: solid directly turns to gas without melting (CO2(s)—>CO2(g)) • deposition: gas to solid (ex: H2O(g)—>H2O(s)) • molecular compounds: not ionic, not covalent—> assembled by intermolecular force • water liquid higher density than ice: fusion line bents left; solid higher density: bends right Phase Diagrams • phase diagram: map of states in (T, P) 2D space — lines represent where two phases coexist. • Solid/gas line: sublimation curve 2 Monday, February 8, 2016 • Solid/liquid line: fusion(melting) curve • Liquid/gas line: vaporization(VP) curve • Triple poin:tall 3 states exist Critical point: furthest point on the vapor pressure curve — above both critical temp(Tc) and • critical preccure(Pc) — the meniscus between the liquid and vapor disappears & the states commingle to form a superficial fluid Unit Cells & Structures of Crystalline Solids • Unit cell: smallest repeating unit of the lattice • coordination number(CN): the number of the nearest neighbor atoms Simple Cubic Unit Cell • Edge/ atom ratio: L=2r —> atoms touch along edges • Packing efficiency: % volume of the unit cell occupied by particles • Coordination number: 6 Body Centered Cubic Cell(BCC) • Edge/atom ration: L= 2( √2 )r —> atoms touch along body diagonal • Coordination number: 8 • equivalent atoms/cell: 2 Face-Centered Cell(FCC) • edge/atoms ratio: 4 • edge length: L= 2( √2 )r—> atoms touch along body diagonal • coordination number: 12 • Packing efficiency: 74% — closed packing Chapter 12 (Solutions - Molarity & Molality): • Solution: molecular(atomic) level dispersion of one substance(solute) in another substance(solvent) - like dissolves like: polar dissolves polar; non polar dissolves non polar • Strong electrolytes: solutions w/ solute of ions, conducting electricity (ex: aq. solution NaCl) 3 Monday, February 8, 2016 • Non-electrolyte: no charge carries (ions) in solution, non conductive (ex: aq. solution of sugar) • Weak electrolyte: have solute of mainly undissociated molecules and a minor portion of molecules disassociated into ions (ex: CH3COOH - 5% disassociation) • Molarity: (M) (moles of solute)/(volume of solution) Molality: (m) (moles of solute)/(kg solvent) — is temperature dependent • • Soluble: maximum solute concentration less that 0.1 M (generally speaking) • Insoluble: maximum solute concentration less than 0.001M • Solubility: The highest concentration in solute in g/100g of solvent - For most solids, the solubility increases as the temperature increases - Gas more soluble at LOW temperature and HIGH pressure - Solubility in solids ONLY depends on Temperature • Cognitive property: Depends ONLY on # of solute particles, NOT on identity • Non- Volatile solute replaces volatile solvent at surface (less particles escape) - solution vapor lower than the solvent - number of ionic particles can be less than the number of ions in the ionic compounds formula to “ion pairing”; for molecular solute, it is 1 - Van’t Hoff factor (i): number of particles in sol/ formula — factors at 0.05m (molality) comparing w/ pure solvent, solutions show Freezing Point Depressions & Boiling Point Elevations - (FPsolvent - FP solution) = change of Tf = imKf - (BPsolution - BPsolvent) = change of Tb = imKb Rules for Solubility - Rule 1: Group 1A metal salts and ammonium salts and all nitrates are soluble - Rule 2: Carbonates, hydroxides, phosphates, sulfite & sulfides are nearly always soluble - Rule 3: Chlorides, bromides, & iodides are always soluble except when with Ag+ or Pb+ - Rule 4: Rule 1 always takes precedence How to Prepare Solutions 4 Monday, February 8, 2016 - weigh solid solute and add solvent (water) - measure volume of concentrated solution & add solvent to dilute it - Dilution Equation: n=M1V1=M2V2 Precipitation Reactions - molecular equation: as if all species are molecular - no precipitate formation —> No reaction - Precipitation is ALWAYS marked w/ (s) after the formula! Ionic Equations & NET Ionic Equations - product must be insoluble - NO spectators (for net ) Osmotic Pressure - Osmosis: net flow of solvent from a dilute solution into a concentrated solution through a semi permeable membrane - Osmotic Pressure(II): pressure needed to stop solvent from moving to a more concentrated region through a semi permeable membrane - π = MRT where M: molarity ; R: 0.08206 (L*atm)/(mol*K); π : Unit : atm, T: Kelvin • Miscible: no limit of solubility - Two liquids that are mutually soluble - Alcohol & water are miscible - Water & oil are immiscible • Super saturated solutions: more solute than the solubility w/ a lack of nucleation centers • Tyndall effect: Colloidal particles scatter light • Colloid: dispersion of particles w/ size between 1 nanometer & 1 micrometer - Aerosol: (solute: liquid; solvent: gas) Fog - Solid Aerosol: (solute: solid; solvent: gas) Smoke - Foam: (solute: gas; solvent: liquid) Whipped Cream - Emulsion: (solute: liquid/ solvent: liquid) Milk - Solid Emulsion: (solute: liquid; solvent: solid) Opal 5 Monday, February 8, 2016 • 6


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