Lecture 3: Announcements - ETH Zurich PDF

Lecture #3, p. 1 Lecture 3: Announcements Today: Brown 4.1 General Properties of Aqueous Solutions 4.2 Precipitation Reactions 4.3 Acids, Bases, and Neutralization Reactions 4.4...

Lecture #3, p. 1 Lecture 3: Announcements Today: Brown 4.1 General Properties of Aqueous Solutions 4.2 Precipitation Reactions 4.3 Acids, Bases, and Neutralization Reactions 4.4 Oxidation–Reduction Reactions 4.5 Concentrations of Solutions Problem Set 2: Due before Exercise #3 tomorrow; upload on Moodle link Problem Set 3: Posted today on Moodle; due before Exercise #4 next week Study Center: Started yesterday! Wednesdays 18:00–20:00 in ETA F 5 Office Hours: Thursdays 17:00–18:00 in LEE P 210 Brisby Chemistry To we Ire t a scout At aboutcalciumdeposits Kalk hi fthe  Lecture #3, p. 2 Lecture 4 Next Week: Brown 5.1 The Nature of Chemical Energy 5.2 The First Law of Thermodynamics 5.3 Enthalpy 5.4 Enthalpies of Reaction 5.5 Calorimetry 5.6 Hess’s Law 5.7 Enthalpies of Formation Chemistry  Lecture #3, p. 3 Review In Lecture 2, we discussed gases Variables needed to describe gases: P, V, T, n Pressure, barometers, and manometers Gas laws (Boyle’s, Charles’s, and Avogadro’s law) Ideal gas law: PV = nRT Standard temperature and pressure (STP) Partial pressures, mole fraction Kinetic-molecular theory of gases Velocities and velocity distributions Molecular diffusion, collisions, and mean free path Chemistry  Lecture #3, p. 4 Nonidealities in Gases si nilmoi Anydeviation isnonideal Chemistry  Lecture #3, p. 5 Nonidealities in Gases: Van der Waals Equation Chemistry tointeractions sowe add nawterm to P sI tE Meaning Them.ieEsuraifraP.Ie tinser www.rgistsf.rd.ee thanthemoleculesexperience Someofthevolumeisnowoccupiedbyothermolecules Thin s fern if gfr  Lecture #3, p. 6 Reactions in Aqueous Solutions Last lecture: gases Today: liquids What is a solution? Homogeneous mixture of two or more substances solution = solvent + solutes Solvent? Substance present in greatest amount iiiIiii Solutes? Substances “dissolved” in solvent Aqueous solutions? Solvent is H2O H2O is unusual in many ways (more later) Good at dissolving ionic solids (e.g. NaCl)... Chemistry man we n n n y.a.am  Lecture #3, p. 7 Electrolyte Substance that dissolves in H2O by forming ions Ionic solid dissociates into individual cations and anions Chemistry  Lecture #3, p. 8 Why is H2O Good Solvent for Ions? willreturn Delta means partial charge theseideas Partial means less than e dtreatin Oxygen has partial negative charge thecoming Hydrogen has partial positive charge H2O orients itself to stabilize charge of ions Chemistry  Lecture #3, p. 9 Nonelectrolyte Substance that dissolves in H2O without forming ions Nonelectrolytes dissolve when individual molecules dissolve in H2O Chemistry wikipedia of Anotherexample anon ethanolmolecules at electrolyticsolution season dissolveas liquidsolute in it so beer su's rose CiaHason  Lecture #3, p. 10 Why Do Substances Dissolve in H2O? Complicated question! Not all substances do Need thermodynamics to determine which dissolve starting next lecture Both energetic and entropic reasons for solute to dissolve System (H2O + solute) System (H2O + solute) lowers its energy increases its disorder For now: accept that by dissolving by dissolving some substances are soluble in H2O and others not soluble Chemistry soluble means it dissolves insoluble means it doesnot  Lecture #3, p. 11 Becausesome substancesdissolveandothersdonotthisleadstoclassofreactionsknownas Precipitation Reactions Precipitate ≡ insoluble solid formed by reaction Ex 1: AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) iii “aq” means aqueous, i.e. dissolved in H2O “s” denotes solid precipitate AgCl (s) used in photographic film Ex 2: 2 Na(C17H35COO) (aq) + CaCl2 (aq) soap = sodium stearate Ca(C17H35COO)2 (s) + 2 NaCl (aq) “soap scum” 4 Exchange or Metathesis Reactions AX + BY AY + BX 9 In preciptiation reactions cations (A,B) and anions (X,Y) trade partners Chemistry re test in  Lecture #3, p. 12 Complete Ionic Equations versus Net Ionic Equations Above, reaction written as “molecular equation,” with all ionic compounds as molecules AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Other ways to write same reaction Remember these reactants are ionic solids that dissolve... Chemistry  Lecture #3, p. 13 Complete Ionic Equations versus Net Ionic Equations Above, reaction written as “molecular equation,” with all ionic compounds as molecules Complete Ionic Equation Ag+ (aq) + NO3− (aq) + K+ (aq) + Cl − (aq) AgCl (s) + NO3− (aq) + K+ (aq) Write out all dissolved ions AgCl is not dissolved; it is precipitate Note: K+ and NO3− are on both sides of equation. Called spectator ions I Net Ionic Equation Cancel spectator ions from both sides of equation Ag+ (aq) + Cl − (aq) AgCl (s) How do we know if precipitate will form? Use solubility chart... Chemistry Ruleofthumb is w.sib.it titties  Lecture #3, p. 14 Solubility for Common Ionic Compounds in H2O T.is.in Lecture 1: Chemistry  Lecture #3, p. 15 mechanical engineers acidbasechemistry Acids Substances that ionize in H2O to form hydrogen cations Acidsalsokno Common acids: as protondon HCl $% → H! $% + Cl"($%) hydrochloric acid monoprotic acids HNO3 $% → H! $% + NO" # ($%) nitric acid gi.im H2SO4 $% → H! $% + HSO" $ ($%) sulfuric acid diprotic acid HSO" $ $% → H! $% + SO%" $ ($%) mtie.it Chemistry after Lectures12and13  Lecture #3, p. 16 Bases Substances that accept (react with) hydrogen cations Bases produce hydroxide ions OH ! when dissolved in H" O Common bases: NaOH %& → Na! %& + OH" %& sodium hydroxide Ca OH 2 %& → Ca#! %& + 2OH" %& calcium hydroxide NH3 %& + H#O ℓ → NH$! %& + OH"(%&) ammonia Chemistry doesnt But havetobe a hydroxidetobeabase Commonexample ammonia NH  Lecture #3, p. 17 Strength of Acids and Bases Depends on how much H! and OH" produced, respectively Quantified by pH scale (discussed in Lecture 13) But reactivity of acid does not just depend on the amount of H! Also depends on the anion Ex: HF $% → H! $% + F " $% hydrofluoric acid Weak acid but still nasty due to F ! Very reactive! Very corrosive! Chemistry HF is boneseeker Exposuretoskin get helpimmediately  Lecture #3, p. 18 e liquid Neutralization Reactions y Nacl ta deifition HCl $% + NaOH $% → H%O ℓ + NaCl($%) (acid) (base) (salt) whichcatio Complete ionic equation: H! $% + Cl" $% + Na! $% + OH" $% → H%O ℓ + Na! $% + Cl" $% Net ionic equation: H! $% + OH" $% → H%O ℓ Neutralization reaction: H # and OH ! combine to form H" O Chemistry  Lecture #3, p. 19 I Ia s bathrooms Were.in Istsa Ine _our Cleaning Limescale (Kalk) Scale from hard water is typically CaCO3 i Precipitation reaction: Ca"# &' + CO"! $ &' → CaCO$ (+) londoncityplumbers.co.uk Neutralization reaction: Use vinegar (acetic acid) to clean CaCO$ + + 2CH$ COOH &' → H" O / + Ca CH$ COO " &' + CO" (0) I insoluble acetic product calcium carbon attation base acid of acetate dioxide sine neutralization (salt) Chemistry s t EE ts IE g  Lecture #3, p. 20 it a'it edureiiatt anion insolublecompound I tiiia.f Then we introduced acidbasereactionswhere a proton istransferredbetweenreactants Now athirdclassofreactionwhereelectron is transferredbetweenreactants AgainfirsttookMore in Lecture 14 Oxidation–Reduction Reactions or “Redox” reactions Classic example: Corrosion ⇒ Reaction between elemental metal and its environment c Rust ⇒ Fe loses electrons to O2 in air ⇒ Fe2O3 Tarnish ⇒ Ag loses electrons to H2S ⇒ Ag2S Chemistry tounderstand I FI i f  Lecture #3, p. 21 Called oxidation becausethefirstsuchreactionsthatwere studied involved ametalthatgaveits electrons to oxygen forming a metaloxide like in rust Fears Oxidation x When an atom, ion, or molecule loses electrons Atom, ion, molecule becomes more positively charged Example: 2 Ca $ + O! ' → 2 CaO ($) Each calcium atom starts as neutral ⇒ Ca2+ (oxidized) Reduction When an atom, ion, or molecule accepts electrons Each oxygen atom starts as neutral ⇒ O2− (reduced) Chemistry  Lecture #3, p. 22 Oxidation and Reduction Go Together! One species gives up electrons, other accepts To remember difference between oxidation and reduction ⇒ “LEO the lion says GER” Losing electrons Gaining electrons is oxidation is reduction Book-keeping system to keep track of transferred electrons? Chemistry  Lecture #3, p. 23 Before proceeding weneed a bookkeepingsystemtokeeptrackof howmanyelectrons aretransferred Oxidation Numbers or oxidation state Each atom in a neutral substance or ion assigned an oxidation number For monoatomic ions ⇒ oxidation number is same as its charge For neutral molecules or polyatomic ions ⇒ oxidation number for each constituent atom is its hypothetical charge molecule Rules to assign oxidation numbers to each atom? Chemistry Inthiscourse wewillfollowconvention used in textbook wealsomentionedthisinlecturet.p.at Is InIn Ex Castcationhas 2 oxidationnumber  Lecture #3, p. 24 Note t seonato 95 I ieIInthef Oxidation Numbers Rules: Atoms in elemental form: 0 Monoatomic ions: ionic charge Nonmetals in ionic/molecular compounds: negative oxidation numbers Oxygen: −2 (except peroxide ion, O!" ! , −1) H: +1 (except if bonded to metal, −1) EiimY'atria F: −1 (always) Cl, Br, I: −1 (except positive if bonded to oxygen) Sum of oxidation numbers for atoms in compound equals its net charge Ex: Mg $ + 2HCl(+,) → MgCl! (+,) + H! (0) 0 +1 −1 +2 −1 0 Mg is oxidized; Mg reduces H; Mg is reductant Or reduce H is reduced; H oxidizes Mg; H is oxidizer Chemistry or a Thesetypes ofreactions between a metal and acid or salt known as displacementreactions A Bx AX B  Lecture #3, p. 25 Howcanwe predictwhichmetals will be oxidized Activity Series Metals listed in terms of ease of oxidation easiest to oxidize...... hardest to oxidize Chemistry i Noble metals are near bottom of activityseries See Table4.5 in Brown forcompletelist Makes Tens I easytocorrode usedasstablecurrency  Lecture #3, p. 26 Wecanuseactivityseries to predict if certainmetal willreactwithanothermetalcation or acid Using Activity Series Any metal can be oxidized by metal cations below it in series As... Cu # + 2Ag # () → Cu!# () + 2 Ag(#) Agbelow c... Any metal above hydrogen in series... can react with acid to form H2 Ni # + 2HCl () → NiCl! () + H! (2) yiat.ve Chemistry These questions of reactivity are important for electrochemistry wewill returntothistopic in Lecture14on batteries Ex Howcan we manipulate the electronflow here forusefulelectrical power  Lecture #3, p. 27 Finally we needlanguage to quantify amount of aqueous solute Concentration Molarity ≡ moles of solute Note: This is not the only way to Iii volume of solution in liters express concentration 1 mol Example: 1 molar solution ⇒ ≡ 1M 1L molarity Need to be able to convert between M, V, and n iii ies Common class of problems on exam Get practice on PS #3 Chemistry NEXT TIME 1ˢᵗ LAW OF THERMODYNAMICS  Lecture #3, p. 28 What We Learned Solutions = solute + solvent Aqueous solutions, electrolytes, nonelectrolytes Precipitation reactions, exchange reactions Molecular reaction, complete ionic reaction, net ionic reaction Acids, bases, neutralization reactions Oxidation–reduction reactions Oxidation numbers, oxidation state Activity series Concentration: molarity Chemistry