Water Why are scientists looking for water on other planets? · 2012-10-24 · Water Why are...
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Water Why are scientists looking for water on other planets? Title: Sep 110:55 AM (1 of 19)
Transcript of Water Why are scientists looking for water on other planets? · 2012-10-24 · Water Why are...
Water
Why are scientists looking for water on other planets?
Title: Sep 110:55 AM (1 of 19)
Cells7095% water
important for chemical reactions condensation
hydrolysis
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Important aspects of water
1. polaritydue to electronegativityoxygen is more electronegative than hydrogen (electrons spend more time near the oxygen)water molecule can bond with 4 other water molecules
(hydrogen bonds)polarity is an emergent property of hydrogen bonding to
oxygen
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2. Cohesion/Adhesion
effect of hydrogen bonds holding the molecule together ("stick" to each other)
helps water create structure
Water molecules continually reform hydrogen bonds (1/20th strength of covalent bond)
Adhesion = clinging of one substance to another
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3. Surface tension
"measure of how difficult it is to stretch or break the surface of the water"
like an invisible film
A water strider can pack 15 times its weight and remain afloat. Here a strider eyes another floating bug. Credit: MIT/Bush, Hu et al.
http://www.livescience.com© 20042007 Imaginova® Corp. All Rights Reserved.
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4. Water's ability to moderate temperature on Earth
stabilizes air temperatureabsorbs from warm air and releases to cool aircan absorb/release large amounts of heat with only
a slight change in its own temperature
heat = total amount of kinetic energy due to motion of a molecule
Temperature = measures the intensity of heat due to the kinetic energy
calorie = the amount of heat energy necessary to raise the temperature of 1 gram of water 1 degree C
kilocalorie = 1000 calories
joule = 0.239 calorie
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5. Has a high specific heat
= the amount of heat that must be absorbed or lost for 1 gram of substance to change temperature by 1 degree C
due to hydrogen bondingbreaking bonds = heat absorbedforming bonds = heat released
ocean temp. doesn't fluctuate muchwarms cool air at night
that is why coastal temps. do not change as much as inland
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6. High heat of vaporization
= quantity of heat that a liquid must absorb for 1 gram of it to be converted from a liquid to a gas
liquid to gas requires a lot of kinetic energy
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7. Evaporative cooling
as liquid evaporates, the surface behind cools
due to lower kinetic energy molecules left behind
high energy kinetic molecules get evaporated
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8. water's states of matter
can be in three states: gas, liquid, solid
ice is less dense than as solid than liquid
above 4 degrees C = liquidexpands when warm, contracts when cools
at 0 degrees C becomes a crystal lattice (solid)10% less dense than liquid at 4 degrees C
ice insulates water below
solid liquid gas
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9. Good solvent
solvent
solute
good solvent because it forms hydrogen bonds with charged and polar covalent molecules
if a substance has an affinity for water = hydrophilicusually ionic or polar bonds
if a substance does not have an affinity for water = hydrophobicusually nonionic and nonpolar bonds
Title: Sep 111:25 AM (11 of 19)
Dissociation of Water molecules
cause:a hydrogen atom shared by two water molecules shifts from one molecule to another
hydrogen atom leaves its electron behind transferred as a single proton
water molecules that lost proton = hydroxide ionwater that gains proton = hydronium ion
reversible reaction
acids and bases can disrupt the concentrations of these ions
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pH
acid
base
pH scale
strong acids and bases dissociate completely in waterHCl H + Cl
weak acids binding and release of hydrogen ions is reversibleH2CO3 HCO3 + H
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neutral pH = 10 M = pH 7
most biological fluids = pH68
What does it mean going from pH 7 to pH 6?
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Buffers= resist changes to the pH of a solution when H or OH is added to solution
accept hydrogen ions from solution if in excess
when hydrogen ions are depleted, it donates them
are usually a weak acid and its corresponding base
important for humansblood (pH 7.35 7.45) is buffered by carbonic acidequilibrium between carbonic acid & bicarbonate regulates pH
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Acid Precipitation
affects water quality/environment
normal rain = pH about 5.55.6
is a product of the formation of carbonic acid from carbon dioxide and water (sulfur oxides, nitrogen oxides)
react with water to form strong acids
occurs when rain, snow, or fog is more acidic than normal
affects development of eggs and developmental stages of aquatic organisms
affects soils washes away nutrients (calcium, magnesium)increases solubility of other compounds ( ie. aluminum) becomes toxic
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Acid precipitation damage to trees
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Acid rain damage
1908 1968
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