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43 Cards in this Set

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  • Back
what % of cells are water
70-95%
water molecules
two hydrogen atoms form single polar covalent bonds with an oxygen atom.
Because oxygen is more electronegative than hydrogen, the region around the oxygen atom has a partial negative charge.
The regions near the two hydrogen atoms have a partial positive charge.
A water molecule is a polar molecule in which opposite ends of the molecule have opposite charges.
hydrogen bonding in water molecules
The slightly negative regions of one water molecule are attracted to the slightly positive regions of nearby water molecules, forming hydrogen bonds.
Each water molecule can form hydrogen bonds with up to four neighbors.
-- weak bonds
-- they last only a trillionth of a second because they break and reform with other molecules
4 emergent properties of water that contribute to earth's fitness for life
cohesion
moderation of temp
insulation of water by floating ice
solvent
cohesion
water molecules bond to each other with hydrogen bonds
this is what allows water olecules to pull each other up through the roots of plants
adhesion
clinging of one substance to another--- water adheres to the walls of the cells
surface tension
the force necessary to stretch or break the surface of a liquid
water has greater surface tension because of hydrogen bonds
how does water moderate earth's temp?
stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.
heat
measure of total kinetic energy (atoms are moving) due to molecular motion in a body of matter
temperature
intensity of heat in a body of matter due to average kinetic energy of molecules
calorie
amount of heat energy necessary to raise the temperature of one g of water by 1°C.
kilocalorie
A kilocalorie is the amount of heat energy necessary to raise the temperature of 1000 g of water by 1°C.
joule
energy unit 0.239 cal
specific heat of a substance
amount of heat that needs to be absorbed for 1 g of substance to raise 1 degree celcius
specific heat of water
1 cal per gram per degree Celsius or 1 cal/g/°C.

higher than most which means it must absorb or lose more heat for its temp to change
why is the specific heat of water high and why is this good for the earth
it takes a lot of energy to break or form hydrogen bonds


A large body of water can absorb a large amount of heat from the sun in daytime during the summer and yet warm only a few degrees.
At night and during the winter, the warm water will warm cooler air.
Therefore, ocean temperatures and coastal land areas have more stable temperatures than inland areas.
Living things are made primarily of water. Consequently, they resist changes in temperature better than they would if composed of a liquid with a lower specific heat.
vaporization/ evaporation
occurs when the molecule moves fast enough to overcome the attraction of other molecules in the liquid.
Even in a low-temperature liquid (with low average kinetic energy), some molecules are moving fast enough to evaporate.
Heating a liquid increases the average kinetic energy and increases the rate of evaporation.
heat of vaporization
quantity of heat that a liquid must absorb for 1 g of it to be converted from liquid to gas.
Water has a relatively high heat of vaporization, requiring about 580 cal of heat to evaporate 1 g of water at room temperature.
evaporative cooling
hotter molecules evaporate making the ave kin energy of the ones behind lower aka cooler
evaporation in organisms
releases heat in sweat and cools organisms down
what happens when water freezes
when the temperature falls the molecules slow down and cant break the hydrogen bonds so they are held at arms length away from each other making it 10% less dense than at 4 degrees
why is water's low density when it freezes good for earth?
If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid.
During the summer, only the upper few centimeters of the ocean would thaw.
Instead, the surface layer of ice insulates liquid water below, preventing it from freezing and allowing life to exist under the frozen surface.
solution
liquid that is completely homogeneous mixture of 2 or more substances
solvent vs solute
solvent = dissolving agent sugar or whatever= solute
aqueous solution
solution where water is solvent
why water is an effective solvent
- polarity of molecules
readily forms hydrogen bonds with charged and polar covalent molecules
- polar molecules are also soluble in water because they form hydrogen bonds with water
0 large molecules can disolve if they have ionic and polar regions
hydration shell
water molecules surrounding dissolved ions
hydrophillic
water loving
dominated by ionic or polar bonds
molecules that are too large dont dissolve (example cotton attracts water but cellulose is too big to be dissolved)
hydrophobic
water fearing
nonionic and have nonpolar covalent bonds
- no consistant regions with partial or full charges so water molecules cannot form hydrogen bonds
- oils
- cell membranes
moles
unit... 6.02x 10 23 molecules
equal to the molecular weight of a substance but scaled up from daltons to grams
advantages to using moles
a mole of one substance has the same number of molecules as a mole of any other substance
- allows scientists to combine substances in fixed ratios of molecules
-
molarity
concentration of a material in solution
- one molar solution has one mole of a substance dissolved in one liter of solvent
h2- <=> H+ + OH
water molecule dissociates into a hydrogen ion and a hydroxide ion

at equilibrium the concentration of water molecules greatly excedes H+ and oh-

both ions are very reactive and changes in concentrations drastically affect the chemistry of a cell
ph scale
how acidic or basic a solution is
1-14
ph= -log[h+] or [h+]= 10-pH
acid
a substance that that increases the hydrogen ion concentration in a solution

hydrochloric acid in water, hydrogen ions dissociate from chloride ions

hcl-> h++ Cl-
each pH unit represents a tenfold difference in h+ and oh- concentrations
small change in pH is large change in concentrations
base
reduces hydrogen ion concentration
some bases directly accept hydrogen ions sych as ammonia nh3

- other bases just dissociate oh- which combines with h+ to form water
strong vs weak acids and bases
strong- molecules disociate completely in water
weak-- binding and release of hydrogen ions are reversible
product of h+ and OH- concentration
always constant at 10-14 in any solution
buffers
resist changes to the ph of a solution when h+ or oh - is added to the solution to maintain cellular pH at a constant level
- usually consist of a weak acid and its corrosponding base
-- example: carbonic acid in human bloodwhich dissociates into bicarbonate ion and ydrogen ion
acid precipitation
occurs when raid snow or fog is more acidic than 5.6
caused primarily by sulfur oxides and nitrogen oxides in atmosphere
react with water to form strong acids that fall to the surface with rain or snow
main source of oxides that cause acid rain
burninf of fossil fuels like coal oil and gas
smokestacks spread the pollution so it effects far away areas
effects of acids in lakes and streams are most pronounced when?
spring during snowmelt. meltwater accumulates acid and brings it to lakes and streams all at once
can impact egga and early developmental stages of aquatic organisms
acid precipitation impact on sols
affects solubility of soil minerals
wash away key soil buffers and plant buffers and increase toxic compounds