Ap bio chp 3

Cohesion

phenomenon of a substance being held together by hydrogen bonds. (water sticks to water)

Adhesion

of water to vessel walls counteracts the downward pull of

gravity. (water sticks to something else).

Surface tension

– measure of how difficult it is to stretch or break the surface of a liquid

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.

Heat of vaporization

– quantity of heat a liquid must absorb for 1 g to be converted to the

gaseous state.

hydration shell

is a blanket of water molecules that wraps around dissolved particles to keep them separated in water.

What type of bonds holds the hydrogen to the oxygen within a water molecule?

Polar covalent bonds hold the hydrogen atoms to the oxygen atom within a single water molecule. Because oxygen is significantly more electronegative than hydrogen, it pulls the shared valence electrons closer to its nucleus.

What type of bond holds water molecules together?

Hydrogen bonds hold separate water molecules together.

Why does ice float?

Ice floats because water expands as it freezes, making solid ice less dense than liquid water.

Hydrophilic

(hydro – water; philo – loving); property of having an affinity for water. Some

large hydrophilic molecules can absorb water without dissolving.

Hydrophobic

(hydro – water; phobos – fearing); property of not having an affinity for water,

and thus, not being water-soluble.

know how to prepare solutions of various concentrations.. prepare 250 ml of a 0.5 molar sucrose

What pH Measures

How many H+ (hydrogen) ions are in a liquid.

Neutral (pH 7):

equal H+ and OH- ions

Acid (pH < 7)

Adds extra H+ ions

Base (pH > 7)

Removes H+ ions (or adds OH-)

Finding Ion Amounts:

Take the pH number and put it in the exponent: a pH of 3 means H+ = 10 ^-3 M. Because H+ AND OH- exponents must total -14, OH- = 10^-11 M.

pH 3 vs. pH 6 Acidity

Moving 3 steps down (6 - 5 - 4 -3) means 10 × 10 × 10 = 1000 times more acidic.

Buffer

substance that minimizes large sudden changes in pH.

Buffer - Are combinations of

of H+

-donor and H+

-acceptor forms in a solution of weak acids or bases

Buffer - Work by accepting

H+

ions from solution when they are in excess and by donating H+

ions to

the solution when they have been depleted

Example of Bicarbonate buffer

pH scale

scale used to measure degree of acidity. It ranges from 0 to 14.

Water molecule that lost a proton has a net negative charge and is called

a hydroxide ion (OH-)

By convention, ionization of H2O is expressed as

the dissociation into H+

and OH-

.

At equilibrium in pure water at

25°C: Number of H+ ions = number of OH- ions.

Mole (mol)

– the number of grams of a substance that equals its molecular weight in daltons and

contains Avogadro’s number of molecules, expressed in grams

Molarity

number of moles of solute per liter of solution, to make a 1M sucrose solution, weigh

out 342 g of sucrose and add water up to 1L.

Molecular mass

the sum of all the masses of all the atoms in a molecule, expressed in daltons

Nonpolar compounds

which have symmetric distribution in charge are not water

soluble, repel water molecules (do not dissolve in water), example – vegetable oil

Ionic compounds

are water soluble (dissolve in water)

- Charged regions of polar water molecules have an electrical attraction to

charged ions

- Water surrounds individual ions separating them from one another

- Forms a hydration shell

Polar compounds

in general are water soluble

- Charged regions of polar water molecules have an affinity for the oppositely

charged regions of other polar molecules

Water is the solvent of life

yes

Solution

a liquid that is a completely homogenous mixture of two or more substances.

Solvent

dissolving agent of a solution.

Solute

substance dissolved in a solution.

Aqueous solution

solution in which water is the solvent.

Evaporative cooling

cooling of a liquid's surface when a liquid evaporates. The surface molecules with the highest kinetic energy are most likely to escape into

gaseous form; the average kinetic energy of the remaining surface molecules is thus lower.

Vaporization

(evaporation) – transformation from liquid to a gas. Molecules with enough

kinetic energy to overcome the mutual attraction of molecules in a liquid, can escape into the air.

A large body of water can act as a heat sink, absorbing heat from sunlight during the day and

summer

and releasing heat during the night and winter as

the water gradually cools. As a result:

i. Water, which covers three-fourths of the planet, keeps temperature fluctuations within a

range suitable for life.

ii. Coastal areas have milder climates than inland.

iii. The marine environment has a relatively stable 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 by one

degree Celsius.

Kilocalorie (kcal or Cal)

amount of heat required to raise the temperature of one kilogram of

water by one degree Celsius

Water has extraordinary properties that emerge as a consequence of its polarity and hydrogen-bonding.

Some of these properties are that water:

a. Has cohesive behavior

b. Resists changes in temperature

c. Has a high heat of vaporization and cools surfaces as it evaporates

d. Expands when it freezes

e. Is a versatile solvent

Water is a

a polar molecule. Its polar bonds and asymmetrical shape give water molecules opposite

charges on opposite sides.