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Chemistry:
Properties of Water
Water, Water Everywhere
• If you have ever seen a photograph of Earth from space, you know
that much of the planet is covered by water. Water makes life on
Earth possible. If life as we know it exists on some other planet,
water must be present to support that life.
• 1. Working with a partner, make a list of ten things that have water in
them.
• 2. Exchange your list for the list of another pair of students. Did your
lists contain some of the same things? Did anything on the other list
surprise you?
• 3. Did either list contain any living things?
Polarity of Water
• Water molecules (H2O) are neutral overall
• Polarity: In a water molecule, the oxygen (with 8
protons in its nucleus) has a stronger attraction
for electrons than the hydrogen (with 1 proton in
its nucleus) = greater chances of finding the
shared electrons near the oxygen atom
• As a result, the oxygen end of the molecule is
slightly more negative (-) and the hydrogen end
is slightly positive (+). This is known as a polar
molecule.
• Polarity is the uneven distribution of electrons.
Polarity of Water
(continued)
• A water molecule is polar because there is
an uneven distribution of electrons
between the oxygen and hydrogen atoms
Oxygen is an “electron-hog”
and most of the electrons
will hang out near the
oxygen.
Hydrogen Bonds
• Water, because it is polar, can attract
other water molecules
• One hydrogen atom of one water molecule
bonds to the oxygen atom of another
water molecule, creating a hydrogen bond
(not as strong as ionic or covalent bonds)
Cohesion
• Attraction between molecules of same
substance (water bonds with water)
• Example: water to water; explains why
drops of water form beads on smooth
surfaces
Water Moderates Temperature
• When water is heated, the water
molecules move around faster = break
hydrogen bonds and eventually increase
temperature
• When water is cooled, hydrogen bonds
reform, a process that releases heat
• Evaporation is a cooling process
Adhesion
• Attraction between molecules of different
substances (water can bond to glass for
example)
• Example: water to glass molecules;
capillary action; graduated cylinder and
meniscus
Mixtures
• Mixture – material composed of two or
more elements or compounds that are
physically mixed together but are not
chemically combined
• Example: salt and pepper; sugar and
sand, etc.
Solutions
• NaCl in water creates Na+ and Cl- ions
which are attracted to water molecules
• Ions become dispersed in water,
forming a solution – all components are
evenly distributed throughout the
solution
Solutions
(continued)
ClCl-
Na+
Na+
Water
Water
Example: In a salt-water solution, table salt is the solute =
substance that is dissolved in water. Water is the solvent =
substance in which solute dissolves
Go to
Section:
Solutions
(continued)
ClCl-
Na+
Na+
Water
Water
Example: In a salt-water solution, table salt is the solute =
substance that is dissolved in water. Water is the solvent =
substance in which solute dissolves
Go to
Section:
Suspensions
• Some materials do not dissolve in water, but separate
into pieces so small that they don’t settle out. The
movement of the water keeps the small particles
suspended = suspensions
• Example: blood and other undissolved particles
remaining in suspension
Acids, Bases, and pH
• Water molecules can react to form ions as
seen below in a chemical equation:
H2 O
(water)
H+
(hydrogen ion)
+
OH-
+
(hydroxide ion)
The pH Scale
• Indicates concentration of H+ in solution
• Ranges from 0 to 14 – at pH of 7,
concentration of H+ ions and OH- ions is
equal = neutral
The pH Scale
(continued)
• Below pH 7 = ACIDIC = more H+ ions than OHions; lower the pH, the more acidic
– Any compound that forms H+ ions in solution
– Strong acids have a pH between 1 to 3
• Above pH 7 = BASIC = more OH- ions than H+
ions; higher the pH, the more basic
– Any compound that produces OH- ions in solution
– Strong bases have a pH between 11 to 14
• Each step on the pH scale is a factor of 10
• Example: pH of 4 has 10 times as many H+ ions
as a pH of 5
The pH Scale
Neutral
Increasingly Acidic
Both extremes can cause
serious side effects from
respiratory problems to
burned skin.
Increasingly Basic
Oven cleaner
Bleach
Ammonia solution
Soap
Sea water
Human blood
Pure water
Milk
Normal
rainfall
Acid rain
Tomato
juice
Lemon juice
Stomach acid
Buffers
• pH of fluids in the human body is between
6.5 to 7.5. Body must keep pH at these
numbers to maintain homeostasis – does
this by dissolved compounds called
buffers – weak acids or bases that react
with strong acids or bases to prevent
sharp, sudden changes in pH