26 Sep 2011

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2.2 The Early Oceans + Properties of Water
-water vital b/c as a solvent, can dissolve more types of substances than others
-substances most likely to collide + react when dissolved
Why H20 such a good solvent?
-O more EN than H -> polar covalent -> since bent, molecule polar (if was linear,
polarity don’t matter)
-2 H20s -> partial (+) on H attracts partial (-) on O -> hydrogen bond
-in aqueous (water-based) solution, H-bonds form btwn water + polar molecs + ions
Hydrophobic-uncharged/nonpolar compounds that don’t interact w/ H20 thru H-
bonds or dissolve
-interact w/ each other instead (weaker than H-bonds)
-H bonds not as strong as covalent/ionic bonds, but more common
How Does Water’s Structure Correlate with its Properties?
-H20 structure + ability to form H-bonds can explain: expands when liquid -> solid,
high specific heat
Cohesion-binding btwn like molecules (H20 cohesive b/c of H-bonds btwn
Adhesion-binding btwn unlike molecules, usually btwn liquid and solid surface (H20
adheres to any surface with polar or charged components)
Meniscus-formed from cohesion btwn surface molec + lower H20 and surface
adhesion to glass
Surface Tension-resistance H20 surface has against forces that depress surface (like
elastic membrane)
-b/c H-bonds exert pulling force/tension at surface, molecs not stable there ->
water more stable when total SA minimized -> resists forces that increase SA
-all liquids have ST (H20s higher b/c lots of H-bonding)
Water Denser as Liquid than Solid
i.e. more molecs of H20 in given volume of liquid water than solid water
Ice -> each molec has 4 H-bonds -> form crystal structure w/ large spaces btwn
Liquid -> extra heat causes H-bonds to break -> crystal structure collapses ->
molecs packed closer
Water has High Capacity for Absorbing Energy
Specific Heat-amnt of E required to raise T of 1g of substance by 1oC
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