Figure 3'2 Hydrogen bonds between water molecules

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Figure 3.2 Hydrogen bonds between water
molecules 
Evolution Living cells are 70-95 H2O H2O covers
3/4 of the planet Solid Liquid Gas
Polarity and H-bonds Polar Bonds
Asymmetrical shape and charge Resist change in
temp Increase heat of vaporization Evaporative
cooling Expands below 4 degrees C Solvent
Maximum of 4 H bonds per H2O molecule
Cohesion Adhesion Surface tension Structural
organization
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Heat and Temperature Kinetic energy the energy
of motion Heat total kinetic energy due to
molecular motion in a body of matter. Temperature
measure of heat intensity due to the average
kinetic energy of molecules in a body of
matter. Calorie (cal) amount of heat it takes to
raise the temperature of one gram of water one
degree Celsius, also the amount of heat that one
gram of water releases when it cools by one
degree Celsius. Kilocalorie (Kcal or Cal) 1000
cal Water has a high specific heat, that is it
resists temperature changes when it absorbs or
releases heat. Specific heat amount of heat
that must be absorbed or lost for one gram of a
substance to change its temperature by one degree
Celsius. Specific heat of water 1 cal per gram
per degree Celsius (1 cal/g/oC Evaporative
cooling Vaporization (evaporation)
transformation from liquid to gas. Heat of
vaporization quantity of heat a liquid must
absorb for 1 gram to be converted to the gaseous
state. Water has a high heat of vaporization at
the boiling point due to hydrogen bonding. (540
cal/g or 2260 J/g Joule 0.239
cal) Evaporative cooling cooling of a liquids
surface when a liquid evaporates. Moderation of
the Earths climate Humidity
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Figure 3.5 The structure of ice
Water density Water is most dense at 4oC Water
contracts as it cools to 4oC As water cools from
4oC to freezing 0oC, it expands and become less
dense due to hydrogen bonding--therefore ice
floats Benefit to life
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Figure 3.6 A crystal of table salt dissolving in
water
Solution Homogenous mixture Solvent Dissolving
agent Solute Substance dissolved Aqueous
solution Water as a solvent Ionic and polar
compounds dissolve in water
Ionic and polar substances are hydrophilic, but
nonpolar compounds are hydrophobic. Hydrophilic
water loving (some large hydrophilic molecules
can absorb water without dissolving). Hydrophobic
water fearing, not water soluble.
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Figure 3.9 A water-soluble protein
Hydration Shell
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There are 2 important quantitative properties of
aqueous solutions solute concentration and
pH. Molecular weight sum of the weight of all
atoms in a molecule (expressed in daltons) Mole
amount of a substance that has mass in grams
numerically equivalent to its molecular weight in
daltons. All substances have the same number of
molecules in a mole 6.02 X 1023 (Avogadros
number). Molarity number of moles of a solute
per liter of solution.
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Acid and Bases At equilibrium in pure water at
25 oC The number of H the number of OH- H
OH- 1/10,000,000 or M 10-7 M Therefore very
few molecules are dissociated (only 1 of
554,000,000). Acid substance that increases
the relative concentration of H of a
solution. Base substance that reduces the
relative concentration of H of a solution. A
solution in which H OH- is neutral H
gt OH- is acidic H lt OH- is basic Strong
acids and bases dissociate completely in
water e.g. HCl and NaOH. i.e. HCl H
Cl- Weak acids and bases dissociate only
partially and reversibly e.g. NH3 (ammonia) and
H2CO3 (carbonic acid) pH Scale In any aqueous
solution HXOH- 1.0 X 10-14 In a neutral
solution both 10-7 M In a basic solution where
H 10-9 M, the OH- 10-5 In a acidic
solution where H 10-5 M, the OH- 10-9 pH
scale scale used to measure degree of acidity
(ranges from 0 to 14) pH negative log10 of the
H expressed in moles per liter. pH of 7 is
neutral pH lt 7 is an acid solution pH gt 7 is a
basic solution
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Figure 3.9 The pH of some aqueous solutions
Most biological fluids are within the pH range of
6 to 8 (some exceptions e.g. stomach acid with a
pH of 2.0) Each pH unit represents a tenfold
difference (scale is logarithmic), so a small
change in pH represents a large change in actual
H.
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Buffers Buffer substance that minimizes large
sudden changes in pH---helps organisms maintain
the pH of body fluids within a narrow
range. Buffers are combinations of H donor and
H acceptor forms in a solution of weak acids or
bases. They work by accepting H ions from a
solution when they are in excess and by donating
H ions to the solution when they have been
depleted. e.g. Bicarbonate buffer H2CO3
HCO3- H H donor H acceptor (weak
acid) (weak base)