Properties of
Water
Chapter 2 Section 2
Objectives
Discuss the unique properties of
water
Differentiate between solutions and
suspensions
Explain what acidic solutions and
basic solutions are
The Water Molecule
Its properties and functions stem
from its chemical structure
It is one of the few compounds
found in a liquid state over the
Earth’s surface
It is a neutral molecule
Is essential for all biological
processes
Structure of Water
Made of 2
hydrogen atoms
covalently bonded
to 1 oxygen atom
Polarity
The electrons are not shared equally
between the oxygen atom and the
hydrogen atoms
This unequal sharing causes partial
charges to occur at opposite ends
of the molecule
A molecule in which the charges are
unevenly distributed is called polar
The polarity of water molecules
also gives it a bent shape
Hydrogen Bonding
 Because of polarity, water molecules are
attracted to each other
 They form hydrogen bonds between the partial
positive charge of the hydrogen atoms of one
molecule to the partial negative charge of
oxygen on another molecule
 Hydrogen bonds are the force of attractions
between hydrogen molecules and other atoms
such as oxygen, nitrogen & fluorine
 These bonds form, break , and reform with great
frequency
 Polarity of water and hydrogen bonding are
responsible for the other properties of water
Properties of Water
Cohesion
Adhesion
Heat Capacity
Solvent nature
Cohesion
 Cohesion is an attraction between molecules of the
same substance
 Water molecules can be involved in as many as 4
hydrogen bonds at the same time, making it
extremely cohesive
 Cohesion causes water molecules to be drawn
together, which is why drops of water forms
beads on a smooth surface
 It is also responsible for surface tension which
makes water acts as if it has a thin “skin” on its
surface
Surface tension also enables small creatures
such as spiders and water-striders to run on
water without breaking the surface
Adhesion
 Adhesion is the attractive force between
molecules of different substances
 For example: water molecules and glass
molecules
 The surface of water becomes curved
because the attraction between the water
and glass molecules is greater than the
cohesion between water molecules
 Adhesion between water and glass
molecules also cause water to rise in a
narrow tube against the force of gravity
 This affect is called capillary action
 Plants use capillary action to draw water
from its roots to its leaves
Cohesion and Adhesion in Action
Trip to ISS
Mini Lab!
How many drops of water can you
get on a penny before it spills over?
Heat Capacity
 Due to multiple hydrogen bonds between water
molecule, it takes a large amount of heat
energy to speed those molecules up and create
a rise in temperature
 Water’s heat capacity, the amount of heat
energy required to increase temperature, is
relatively high
 This allows:
Bodies of water to absorb large amounts of
heat with only small changes in temperature
Cells to regulate temperature
Stabilizing of global temperatures
Evaporative cooling
Water Mixtures
 Water is not always pure
 It is often part of a mixture
 A mixture is a material composed of two or more
elements that are physically combined and not
chemically combined
 For example:
 Salt & pepper
 Sugar & sand
 Air
 Living things are mixtures involving water
 Two types of mixtures with water:
 Solutions
 Suspensions
Solutions
 A solution is a mixture in which 1 or more
substances are uniformly distributed in another
substance
 They can be mixtures of liquids, solids, or gases
For example: Blood Plasma
 They are made up of two components: the solute
& the solvent
 Water’s polar nature allows it to dissolve polar
substances
Examples: sugar, ionic compounds, some
proteins
Solute
vs.
Solvent
Is a substance
dissolved in the
solvent
Is the substance
that does the
dissolving
Can be ions, atoms,
or molecules that
are dispersed
Example: water
(universal)
In a solution of sugar water, sugar is the
___________ and water is the ____________.
Solutions Continued
Solutions can have varying concentrations
which is the amount of solute in a
certain amount of solvent
Example: 5% saltwater solution is 5g of
salt dissolved into 100 mL of water
Saturated solution: is one in which no
more solute can dissolve
Aqueous solution: is one in which water is
the only solvent
Suspensions
Some materials do not dissolve when
placed in water, but separate into pieces
so small that they do not settle out
The movement of the water molecules
keeps the small particles suspend
Mixtures of water and undissolved
material are called suspensions
Some of the most important biological
fluids are both solutions and suspensions
For example: blood
Blood as a Solution &
Suspension
Ionization of Water
Occurs when water molecules are pulled
apart or dissociate into ions
Hydroxide ion
When this happens it leaves hydrogen to
bond with another water molecule forming
the hydronium ion
Hydrogen ion
pH
Chemists devised a
measuring system called
the pH scale to indicate
the concentration of H+
ions in solution
The pH scale ranges from
0 to 14
Each step on the pH scale
represents a factor of 10
pH Determinations
 The pH of a solution is determined by the
amount of hydrogen ions or hydroxide ions
present
 At a pH of 7, the concentration of the H+
ions and OH- ions is equal so its called
neutral
 Solutions with a pH below 7 are called
acidic because they have more H+ ions than
OH- ions
 Solutions with a pH above 7 are called basic
because they have more OH- ions than H+
ions
Acids & Bases
Acids
Bases
 Is any compound that
forms H+ ions in solution
 Is any compound that
forms OH- ions in solution
 Strong acid pH values
range from 1 to 3
 Strong base pH values
range from 11 to 14
 Tend to have a sour taste
 Can be corrosive
 Tend to have a bitter
taste
 For example
 Tend to feel slippery
 HCl
 H2SO4
 For example:
 NaOH
 NaHCO3
Buffers
 The pH of the fluids within most cells in
the human body must generally be kept
between 6.5 and 7.5
 If the pH is higher or lower it affects the
chemical reactions within the cells
 Controlling pH is a matter of homeostasis
and is done using buffers
 Buffers are weak acids or bases that can
react with strong acids or bases to prevent
sudden changes in pH
 For example: bicarbonate and phosphate ions