NOTES: 2.2 –Properties of Water
WATER OVERVIEW:
• Water is perhaps the most important compound in living organisms
• Because so many substances can dissolve in water:
molecules and ions are free to move and collide with one another in the reactions of life;
water serves as a means of material transportation (i.e. ,)
• Living cells are water
• Water covers approx.
• In nature, water naturally exists in all 3 states of matter:
WATER IS A POLAR MOLECULE…
• the bonds that hold the hydrogen and oxygen atoms together are …
this means that the electrons that make up the covalent bonds are shared UNEQUALLY…they spend
more time near the oxygen atom than they do near the hydrogen atom
so, a water molecule has a
• POLAR WATER MOLECULES attract one another, as well as ions and other polar molecules
• The polarity of water molecules results in
• a HYDROGEN BOND is the attraction of opposite charges between hydrogen and oxygen
• Each water molecule can form a maximum of 4 hydrogen bonds with neighboring water molecules
Properties of Water (as a result of polarity and H-bonding):
► COHESION:
• contributes to upward movement of water in plants from roots to leaves
► ADHESION: (by polarity or H bonds); can counteract gravity in plant vessels
► SURFACE TENSION: measure of how difficult it is to stretch the surface of a liquid
-water has greater surface tension than most liquids because at the air/water interface the surface
water molecules are H-bonded to each other and to the water molecules below
-causes water to “bead”
-
► HIGH SPECIFIC HEAT ()
• Specific Heat: amt. of heat that must be absorbed or lost for 1 gram of a substance to change its temp by 1°C
• Water’s high specific heat means that it resists temp. changes when it absorbs or releases heat
*Heat is absorbed to break H-bonds; and given off when they form
► HIGH HEAT OF VAPORIZATION
• Heat of vaporization = amt. of heat a liquid must absorb for 1 g to be converted to gas state
• for water molecules to evaporate, , which requires heat energy
► EVAPORATIVE COOLING: after high temp. molecules have evaporated, the remaining liquid is cooler
(ex: )
-stabilizes temp. in aquatic ecosystems
-
(as 1 g of water evaporates from our skin, 539 g of body cools by 1°C)
► WATER EXPANDS WHEN IT FREEZES
• because of H-bonding, water is less dense as a solid than it is as a liquid...!
• since ice is less dense, it forms on the surface at first
• as water freezes, it releases heat to the water below and insulates it!
• !!
► WATER IS THE SOLVENT OF LIFE
• due to its polarity, water is a versatile solvent
Mixtures and Solutions:
•MIXTURE: a combination of 2 or more pure substances in which the individual components retain their own properties
•Examples: ;
SOLUTIONS:
•SOLUTION: a mixture in which the solute(s) are evenly distributed in the solvent
•Example:
**!!
•SOLUTE: the
•SOLVENT: the substance in which the solute dissolves ()
Compounds that are HYDROPHILIC (“water loving”), and are soluble in water:
• ionic compounds: charged regions of polar water molecules have an electrical attraction to charged ions
• polar compounds: charged regions of polar water molecules are attracted to oppositely charged regions of other polar molecules
Compounds that are HYDROPHOBIC (“water fearing”) and are insoluble in water:
• Nonpolar compounds: symmetric distribution in charge, or composed of nonpolar bonds
► THE PROCESS OF DIFFUSION:
• DIFFUSION is the net movement of particles from an area of to an area of
it results from the random motion of molecules / particles
Diffusion is affected by three key factors:
1) Concentration: the more concentrated a substance, the
2) Temperature: an increase in temperature will
3) Pressure: an increase in pressure will speed up molecular movement and, therefore, diffusion
**once substances are evenly distributed, no further change in concentration will occur…this is known as DYNAMIC EQUILIBRIUM.
• DIFFUSION is one of the methods by which cells move substances:
cell (bring oxygen into cell; release CO2 to outside of cell);
(ions dissolved in the cytoplasm remain evenly distributed within cell); and
(oxygen diffuses into the blood capillaries in the lungs because it is more concentrated in the air sacs).
ACIDS & BASES
• In living things, chemical reactions depend on the pH of the environment
•Water molecules (H2O) can split apart
•When H+ and OH- are present in equal amounts, the solution is .
•ACID: a compound that (& adds H+ ions to the solution)
•BASE: a compound that (& adds OH- ions to the solution)
• pH =
The pH scale:
• ACID:
• BASE:
BUFFERS
•BUFFERS: dissolved compounds that
•example: blood contains a number of buffers that help maintain a