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Water and Aqueous Cheimstry.docx

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David Brock

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Water & Aqueous Chemistry (Chapter 5) Unique Macroscopic Properties Essential to life 1. Unusually high boiling point of liquid water at STP: bp = 100C at 1 atm (seal level)  T, P – dependent 2. Density of ice (0.92 g/mL) < liquid water (1 g/mL) at 0C: ice expands without freezing: lower packing density 3. High specific heat capacity of water (74 J/molK at STP): absorbs thermal heat for storage/distribution/release 4. Water dissolves a variety of solutes as a solvent: strong solvation properties for most polar molecules/ions i-Clicker question: H bonding intermolecular force accounts for high bp - High electrostatic interactions due to large dipole moment of H bonding accounts for water’s high bp Solute Solvation by Water - Solubilisation of polar/ionic solutes: hydration - Energetically favourable H2O-solute interactions: o H bonding (dipole-dipole) with solutes (O-H, N-H, C=O) o +/- ion-dipole forces - Charged dissolve charged, uncharged dissolves uncharged - Encompassing solutes via these interactions since pos / neg dipoles attract to stabilize Properties of Water Vital for Molecular Behaviour - Ion hydration, sodium pumps, ion transport eg. Sodium ion - Solubility, toxicity, bioaccumulation eg. DDT - Protein folding, activity, and drug binding eg. HAS (human serum abumin) Auto-ionization of Water - Water auto-ionizaiton: water is amphoteric and conductive - water acts as an acid and base with itself - 2H2O(l)   H30 (aq) + OH (aq) (hydronium and hydroxide are electrolyes) - Kw = [H3O+][OH-} = 1 x 10 -14(25C) - Water is a pure liquid so it has a value of 1 so don’t inclue it in equilibrium expression - Kw is always obeyed, regardless of when stresses are added - Ions aren’t concentrated enough to conduct electricity - Purified de-ionized water; pH = -log[H3O+] 7.0 - Low conductivity since [H3O+] & [OH=] = 0.1 µM Solute Properties & Electrolytes - Non-electrolyte: neutral molecule - Strong electrolyte: fully charged ions - Weak electrolyte: partially ionized molecule - Degree of ionization of an electrolyte in aqueous solution , tells how strong the electrolyte is - Strong electrolyte (ionic) eg. Sodium chloride, intravenous supply of electrolytes o NaCl  Na+ (aq) + Cl- (aq) - Weak electrolytes (ewakly ionic): acetic acid: vinegar (5-8% w); preservative / sour – o CH3COOH (aq) + H2O (l)  CH3COO (aq) + H3O+ (aq) (conductive ions) - Non-electrolyte (neutral): ethanol: vodka (>40% v); spirit, depressant, diuretic iClicker Q # 2: strongest conductor – (NH ) SO higher the charge and the greater the number of ions, 4 2 4 the better the conductor / better electrolyte Major Types of Aqueous Chemical Reactions 1. Solubility or Precipitation Reactions (ion transfer) a. Cu(NO3)2 + 2NaOH(aq)  Cu(OH)2 (s) + 2NaNO3(aq) 2. Reduction-Oxidation (Redox) Reactions: (electron transfer) 2+ 2+ a. Zn(s) + Cu (aq)  Zn (aq) + Cu(s) 3. Acid-Base Reactions: (proton transfer) a. CH3COOH (aq) + H2O (l)  CH3COO- (aq) + H3O + (aq) K is a measure of extent of c
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