Ch 5 (Water as Solvent & Aqueous Chemical Reactions)

Ch 5 (Water as Solvent & Aqueous Chemical Reactions) -...

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1 CHEM 1A03: Intro. Chemistry I Water & Aqueous Chemistry Ch.5: Reactions in Aqueous Solutions 1 Water: A Vital Natural Resource! Significance of Water: Energy, Health & Environment “No single measure would do more to reduce disease and save lives in the developing world than bringing safe water & adequate sanitation to all.” UN Secretary-General Kofi Annan, 2003 International Year of Freshwater 2 Water is probably the only natural resource to touch all aspects of human civilization —from agricultural and industrial development to the cultural & religious values embedded in society.” Koichiro Matsuura, Director-General, UNESCO Properties of Water Vital for Molecular Behaviour Protein Folding, Activity & Drug Binding Ion Hydration, Sodium Pumps & Ion Transport 3 Human Serum Albumin (HSA) Sodium Ion Dichlorodiphenyl-trichloroethane (DDT) Solubility, Toxicity & Bioaccumulation Cl Cl Cl Cl Cl iClicker Question #1 Which intermolecular force accounts for water’s unusual high b.p.? (a) Ion-dipole (b) Dipole-dipole (c) H-bonding (d) Van der Waals 4 (e) none of the above Hydrogen bonds: possible because of water’s extreme polarity O H H δ+ δ− Molecular Dipole Water: An Enigmatic Medium! Unique Macroscopic Properties Essential to Life 1. Unusually high boiling point (b.p.) of liquid water at STP: bp = 100 o C at 1 atm (Sea level) Æ T,P-dependent 2. Density of ice (0.92 g/mL) < liquid water (1 g/mL) at 0 o C: Id i t h f i Lk i d i t 5 Ice expands with freezing: Lower packing density 3 . High specific heat capacity of water (74 J/mol . K 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 41 Anomalies of Water: http://www.lsbu.ac.uk/water/anmlies.html ± Solubilization of polar/ionic solutes: Hydration ± Spontaneous ( Δ G o < 0) favorable H 2 O-solute interactions: H-bonding (dipole-dipole) with solutes (O-H, N-H , C=O) +/- ion-dipole forces Solute Solvation by Water I di l i t ti Hydration 6 CH 3 CH 2 O-H Dipole-dipole interactions Na + δ - δ + δ + δ - δ + δ + δ + δ + δ + δ + δ + δ + δ + δ + δ - δ - δ - δ - Ion-dipole interactions Cl - δ - δ + δ + δ - δ + δ + δ + δ + δ + δ + δ + δ + δ + δ - δ - δ - shell δ + δ - δ− δ− δ− δ + δ + δ + δ + δ + δ + .. ..
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2 ± Water auto-ionization: Water is a mphoteric & conductive Auto-ionization of Water 2H 2 O (l) H 3 O + (aq) + OH - (aq) K w Water acts as acid & base with itself! H H .. - + O O Acid Hydronium Transition State 7 K w = [H 3 O + ][OH - ]= 1 x 10 -14 (25 o C) Purified De-ionized Water: pH = -log[H 3 O + ] = 7.0 Low conductivity since [H 3 O + ] & [OH - ] = 0.1 μ M Electrolytes Why isn’t [H 2 O] included in equilibrium expression? H O H H O H H O H H H H Base Hydroxide .. Solute Properties & Electrolytes Non-electrolyte Strong electrolyte Weak electrolyte 8 Neutral molecule Fully charged ions Partially ionized molecule Degree of ionization of an electrolyte in aqueous solution!
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This note was uploaded on 03/01/2011 for the course CHEM 1a03 taught by Professor Landry during the Spring '08 term at McMaster University.

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Ch 5 (Water as Solvent &amp; Aqueous Chemical Reactions) -...

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