What are the
Properties of Water
• Polarity
• Attraction- cohesion,
adhesion, surface
tension, & capillary
action
• High specific heat
• Density – greatest at
4oC
• Universal solvent of
life
What is Polarity of Water
• A water molecule with an
uneven distribution of
charges in different regions
of the molecule
• Water has a variety of unusual properties
because of attractions between these polar
molecules.
– The slightly negative regions of one molecule are
attracted to the slightly positive regions of nearby
molecules, forming a hydrogen bond.
Fig. 3.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is a Hydrogen Bond?
Hydrogen bond is a weak
attraction between a
hydrogen atom and
other atom
Properties of Water
Covalent bonding vs. Hydrogen bonding
Hydrogen Bond
Covalent Bond
What is Cohesion
• cohesion = water attracted to
other water molecules
because of polar properties
What is Cohesion?
Hydrogen bonds hold the
• Cohesion is responsible substance together, a
for the transport of the phenomenon called
COHESION
water column in plants
• Cohesion among water
molecules plays a key
role in the transport of
water against gravity in
plants
What is Adhesion?
•Water attracted to
other materials
What is surface tension?
Surface tension, a measure
of the force necessary to
stretch or break the surface
of a liquid, is related to
cohesion.
Surface tension
– Water has a greater surface tension than most
other liquids because hydrogen bonds among
surface water molecules resist stretching or
breaking the surface.
– Water behaves as if
covered by an invisible
film.
– Some animals can stand,
walk, or run on water
without breaking the
surface.
Fig. 3.3
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is capillary action?
It is the tendency of water
to rise in a thin tube.
Capillary Action
Because water has both
adhesive and cohesive
properties, capillary action is
present.
Capillary Action = water’s adhesive property is the cause
of capillary action. Water is attracted to some other
material and then through cohesion, other water
molecules move too as a result of the original adhesion.
Ex: Think water in a straw
Ex: Water moves through trees this way
What is specific heat?
Specific Heat is the amount of
heat that must be absorbed or
lost for one gram of a
substance to change its
o
temperature by 1 C.
Moderates Temperatures on Earth
Water stabilizes air temperatures by absorbing heat from
warmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heat
with only a slight change in its own temperature.
Celsius Scale at Sea Level
100oC
Water boils
37oC
23oC
Human body
temperature
Room temperature
0oC
Water freezes
•
•
•
•
•
What is kinetic energy?
Heat?
Temperature?
Calorie?
What is the difference in
cal and Cal?
• What is specific heat?
Specific heat
Three-fourths of the earth is covered
by water. The water serves as a
large heat sink responsible for:
1. Prevention of temperature
fluctuations that are outside the
range suitable for life.
2. Coastal areas having a mild
climate
3. A stable marine environment
What is Density
It when hydrogen bonds in water expand
as it warms and contracts as it cools. The
hydrogen bonds keeps the molecules far
enough a part to make ice have fewer
molecules.
Solid – water molecules
are bonded together –
space between fixed
Liquid – water molecules
are constantly bonding
and rebonding – space is
always changing
Density of Water
• Most dense at 4oC
• Contracts until 4oC
• Expands from 4oC to
0oC
The density of water:
Mass-to-volume ratio of a substance; measure of how tightly matter
is packed
1. Prevents water from freezing from the bottom up.
2. Ice forms on the surface first—the freezing of the water
releases heat to the water below creating insulation.
3. Makes transition between season less abrupt.
– When water reaches 0oC, water becomes locked
into a crystalline lattice with each molecule bonded
to to the maximum of four partners.
– As ice starts to melt, some of the hydrogen bonds
break and some water molecules can slip closer
together than they can while in the ice state.
– Ice is about 10% less dense than water at 4oC.
Fig. 3.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is Solvent for Life
• Solution
– Solute
– solvent
• Aqueous solution
• Hydrophilic
– Ionic compounds
dissolve in water
– Polar molecules
(generally) are water
soluble
• Hydrophobic
– Nonpolar compounds
Mixtures with Water
.
• A solution is another name for a homogeneous
mixture.
• In a solution, there are two components:
• A solvent is a substance in which another
substance is dissolved.
• A solute is the substance that is dissolved in the
solvent.
Copyright © McGraw-Hill Education
Water and Solutions
Mixtures with Water
Acids and bases
• Many solutes readily dissolve in water because of
water’s polarity.
• Substances that release H+ when they are dissolved
in water are called acids.
• Substances that release hydroxide ions (OH−) when
they are dissolved in water are called bases.
Copyright © McGraw-Hill Education
Water and Solutions
Mixtures with Water
pH and buffers
• The amount of hydrogen or hydroxide ions in a
solution determines the strength of an acid or base.
• The measure of concentration of H+ in a solution is
called pH.
• Acids have pH values < 7; bases have pH values
>7
• Buffers are mixtures that can react with acids or
bases to keep the pH within a particular range.
Copyright © McGraw-Hill Education
Water and Solutions