Chapter 3 Flashcards
How much of Earth’s surface is covered in water?
3/4s
What is water’s molecular shape and why?
wide V, because oxygen is more electronegative than hydrogen, causing polar covalent bonds = polar molecule
charges of oxygen and hydrogen?
oxygen= slightly neg hydrogens = slightly pos
properties of water due to:
attractions –> hydrogen bonds
____ _____ bonds in water molecules result in hydrogen bonding.
polar covalent
four key properties of water
cohesive behavior
ability to moderate temperature
expansion upon freezing
versatility as a solvent
cohesion
collective hydrogen bonds that hold substance together
contributes to transport of water and dissolved nutrients against gravity in plants (eg. hydrogen bonds cause water molecules leaving veins of leaf to tug on molecules further down)
adhesion
clinging of one substance to another
helps counter downward pull of gravity of water to molecules of cell walls
surface tension
measure of how difficult i tis to stretch/break the surface of a liquid
hydrogen-bonds between water molecules give it a high surface tension
How does water moderate temperature?
It absorbs heat from warmer air and releases stored heat to colder air
Can absorb relatively large amount of heat with only a slight change to its own temp
kinetic energy
energy of motion
faster a molecule = greater KE
thermal energy
related to temperature; KE associated w/ random movement of atoms/molecules
temperature
measure of energy that represents the average KE of the molecules in a body of matter, regardless of volume
total thermal energy
depends on matters’ volume
when two objects w/ different temperatures are brought together:
thermal energy passes form waker to cooler object until the two are the same temperature
heat
thermal energy in transfer from one body of matter to another
calorie (cal)
unit of heat; amount of heat it takes to raise the temperature of 1 g of water by 1 C.
kilocalorie (kcal)
1k calories; quantity of heat required to raise temperature of 1 kg of water by 1 C
joule (J)
0.239 cal; 4.184 J = 1 cal
specific heat
amount of heat the trust be absorbed/lost for 1 g of that substance to change its temperature by 1 C
water’s specific heat
1 cal/g x C
Why is water’s specific heat so high?
hydrogen bonds must be broken 1st before water molecules can begin moving faster
Why is water’s specific heat so important?
large body of water can absorb/store huge amount of heat while warming only a few degrees
at night/winter, gradually cooling air can warm the air; moderates temperatures in coastal areas
stabilizes ocean temperatures, creating favorable enviro
keeps temperature fluctuations within limits that permit life
evaporation/vaporization
transformation from liquid to gas
heat of vaporization
quantity of heat a liquid must absorb for 1 g to be converted from liquid to gas
water’s heat of vaporization and benefits
580 cal of heat needed
results from strength of hydrogen bonds
helps moderate Earth’s climate (moist air forms air)
accounts for severity of steam burns
evaporative cooling and benefits
surface of liquid that remains behind after evaporation cools down
occurs b/c hottest molecules (greatest KE) most likely to leave as gas
contributes to stability of temperatures in lakes and ponds
provides mechanism against overheating (eg. sweating, etc)
Water is less dense as a solid because:
of hydrogen bonding
hydrogen bonds cause it to freeze in a crystalline lattice, keep molecules far enough apart to make ice 10% less dense than liquid water
Water’s greatest density is at:
4 C and begins to expand as molecules move faster
benefits of lower density of ice
stability of enviro for life
if ice sank, all ponds, lakes, oceans freeze solid
insulates the water below
provides solid habitats
global warming has caused:
raise in temperature, which affects seasonal balance, causing ice to melt
solution
liquid that’s completely homogenous and is a mix of 2+ substances
solvent
dissolving agent of a solution
solute
dissolved substance
aqueous solution
solute is dissolve in water (solvent)
hydration shell
sphere of water molecules around each dissolved ion
Water is a versatile solvent because:
it’s polar
Water can dissolve:
ionic compounds, nonionic polar molecules, proteins
hydrophilic
water loving
Can molecules be hydrophilic and not dissolve?
Yes (eg. cotton, which is made of cellulose; molecules are so large they don’t dissolve)
hydrophobic
nonionic, nonpolar, don’t form H bonds, repel water (eg. veggie oil)
molecular mass
sum of the masses of all the atoms in a molecule
mol
exact number of objects; 6.022 x 10^23 (aka Avogadro’s number)
A mol of one substance has:
exactly the same number of molecules as a mol of any other substance
(eg. if substance A has 342 daltons and substance B has 10 daltons, then 342 g of A will have same # of molecules as 10 g of B)
molarity
number of moles of solute per liter of solution
Mars is known for:
having ice under its surface, water vapor exists in the atmosphere and forms frost
__ and ___ conditions affect living conditions.
acidic, basic
hydrogen ion
(H+) transferred between 2 water molecules
hydroxide ion
water molecule that’s lost a proton (OH-), neg charge
hydronium ion
water molecule w/ additional proton (H3O+)
Can H+ exist on its own?
No
At the equilibrium point of the hydrogen reaction:
the concentration of water molecules greatly exceeds the concentrations of H+ and OH-
OH- and H+ are:
very reactive
changes in OH- and H+ concentrations:
can affect a cell’s proteins and other complex molecules
acid
substance that increases the hydrogen ion concentration of a solution (eg. HCl)
removes hydroxide ions b/c of tendency for H+ to combine with OH-, forming water
base
reduces the hydrogen ion concentration of a solution (eg. NH3)
accept hydrogen ions or disassociate to form hydroxide ions (combine w/ hydrogen ions to form water)
increases OH- concentration, but also reduces H+ concentration by formation of water
neutral solution
OH and H concentrations are equal
weak acids and strong bases
disassociate completely when mixed with water, as single arrows
weak acids
acids that reversible release and accept back hydrogen ions (eg. carbonic acid)
product of [H+][OH-]
10^-14, in any aqueous solution at 25C
pH
negative log of the hydrogen ion concentration
pH = -log[H+]
pH declines as H+ concentration increases
pH less than 7= acidic; pH more than 7 = basic, pH = 7 is neutral
each pH unit represents tenfold difference in H+ and OH- concentrations
Does a slight change in pH have any affect on living cells?
Yes; b/c chem processes of cell are very sensitive to concentrations of hydrogen and hydroxide ions
buffer
substance that minimizes changes in concentrations of H+ and OH- in a solution
does so by accepting hydrogen ions from the solution when they’re in excess and donating hydrogen ions when they’ve been depleted
most solutions contain weak acid and its corresponding base, which combine reversibly w/ hydrogen ions
acid-base pairs
carbonic acid
H2CO3, formed when CO2 reacts w/ water in blood plasma
dissociates to yield bicarbonate ion (HCO3-) and hydrogen ion (H+)
chem equilibrium between carbonic acid and bicarbonate acts as pH regulator
burning of fossil fuels
adds CO2 to air, may harm marine ecosystems
ocean acidification
when CO2 dissolves in seawater, forms carbonic acid, lowers ocean pH
cause carbonate ion concentration decr. by 40% by 2100 –> bad c/ carbonate ions needed for calcification (build shells and corals)
calcification rate in a coral reef
predict that acidification will lower concent. of dissolved carbonate ions
