The biological medium on Earth
All living organisms require water more than any other substance
75% of the earths surface is covered in water
Cells are about 70–95% water

Polar molecule: The opposite ends have opposite charges
Polarity allows water molecules to form hydrogen bonds with each other

Cohesive and adhesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent

Cohesion;

Cohesion helps the transport of water against gravity in plants

An attraction between different substances, for example, between water and plant cell walls

A measure of how hard it is to break the surface of a liquid

The energy of motion
Anything that moves has kinetic energy - atoms
The faster, the more energy

A measure of the total amount of kinetic energy due to molecular motion
Heat depends on the volume
Heat and Temperature are NOT the same

Measures the intensity of heat due to the average kinetic energy of molecules

A measure of temperature using Celsius degrees (°C)

At sea level, water freezes at 0°C and boils at 100°C

Is the amount of heat required to raise the temperature of 1 g of water by 1°C

Is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC

Hydrogen bonding;
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form
The high specific heat of water minimizes temperature fluctuations to within limits that permit life

Large bodies of water can absorb and store a huge amount of heat from the sun
Since organisms are made of water, they can resist changes in their own temperature as well

Transformation of a substance from liquid to gas
Molecules moving very fast can enter the air as gas
Any liquid at any temperature evaporates
Increasing the temperature increases the speed

The heat a liquid must absorb for 1 g to be converted to gas
Double that of alcohol or ammonia

Evaporative cooling;

The fastest molecules are also the “hottest” and are most likely to leave as a gas
Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

Hydrogen bonds in ice are more “ordered,” making ice less dense
Water reaches its greatest density at 4°C
At 0C, water locked into a lattice
Keeps molecules of H2O far enough apart to be 10% less dense than liquid water

A liquid that is a homogeneous mixture of substances

The dissolving agent of a solution

The substance that is dissolved

One in which water is the solvent

Because of its polarity, which allows it to form hydrogen bonds easily
When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell.

Water can also dissolve compounds made of nonionic polar molecules

is one that has an affinity for water

is one that does not have an affinity for water;

• Oil molecules are hydrophobic because they have relatively nonpolar bonds
  Hydrophobic molecules related to oils make up cell membranes

Water

• Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution

The sum of all masses of all atoms in a molecule.

• Numbers of molecules are usually measured in moles, where 1 mole (mol) = 6.02  1023 molecules

The number of moles of soluteper liter of solution

Dscribe whether a solution is acidic or basic (the opposite of acidic)

• Adding certain solutes, called acids and bases, modifies the concentrations

Any substance that increases the H+ concentration of a solution
When HCl is added to water H+ ions disassociate
Is acidic as there is more H+ than OH- in the solution

Any substance that reduces the H+ concentration of a solution
Sodium hydroxide in water disassociates into Na and OH-

The negative logarithm of H+ concentration, written as pH = –log [H+]
For a neutral aqueous solution [H+] is 10–7 = –(–7) = 7

Have pH values less than 7

Have pH values in the range of 6 to 8- Neutral = 7

Have pH values greater than 7

pH 7

• The slightest change can be deadly!
  Blood 7.4
  Increase or decrease by .4 – death in minutes!

Are substances that minimize changes in concentrations of H+ and OH– in a solution
Accept hydrogen ion when in access and give hydrogen ions when they are rare