HYDROLOGY
Hydrosphere
~71% of Earth’s surface is covered in
water
What sets Earth apart from other planets
Not always here
4.5 BYA Volcanic Eruptions
– Lava – hot
– Gas – water vapor
– Ash – blocks sun
• Cools temperature
Water vapor condenses
Rain falls
Oceans form
Water Conservation
Most of the water on Earth is not suitable
for human use
97% is saltwater
80% of all freshwater is frozen in polar
ice caps
the majority of remaining freshwater is
polluted or otherwise unsuitable for use
1/3 of Earth’s population does not have
access to suitable water
– Landforms
– Vegetation
– Distance to a body of water
– Drought
– Contamination
– Pollution
The one drop from our experiment is not
available to people all the time.
Properties of Water
Most important compound on Earth
Tasteless
Odorless
2 Hydrogen atoms to 1 Oxygen atom
Polarity
Universal Solvent
Cohesion
Adhesion
Specific Heat
Density
Polarity
The hydrogen and oxygen atoms are
connected by polar covalent bonds
– unequal sharing of electrons
Since the oxygen is bigger than
hydrogen, the electrons tend to stay
closer to the oxygen
– Oxygen has a slightly negative charge
– Hydrogen end has a slightly positive charge
Water Molecule
Polarity creates poles in water molecules like
a magnet.
Water has a variety of unusual properties
because of attraction 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.
– Each water molecule can form hydrogen
bonds with up to 4 neighbors.
Hydrogen Bonds
Hold water molecules Extraordinary Properties that
together are a result of hydrogen
Each water molecule can form bonds:
a maximum of 4 hydrogen – Cohesive behavior
bonds – Resists changes in temperature
– High heat of vaporization
The hydrogen bonds joining
– Expands when it freezes
water molecules are weak,
– Versatile solvent
about 1/20th as strong as
covalent bonds.
They form, break, and reform
with great frequency
Polar = uneven distribution of electrons
– Has a charge
Nonpolar = even distribution of electrons
– No charge
Like dissolves like
– Polar dissolves polar
– Nonpolar dissolves nonpolar
Universal Solvent
Water is an universal solvent
– Most substances will dissolve in water
Ex. Salt dissolves in water
Solvent: substance in which other
substances dissolve
– water
Solute: substance that dissolves
– salt
Why does salt dissolve in water?
Positively charged sodium ions attract the
negative oxygen side of water.
Negatively charged chloride ions attract the
positive hydrogen side of water
Water as a Solvent
Substances dissolved in fresh and salt
water that are important
– Dissolved gases: oxygen and carbon dioxide
– Dissolved salts and minerals/nutrients
(not nitrates)
Adhesion
Adhesion: molecules that are not alike are
attracted
– Ex. Water to walls of a test tube or plant
walls
– Think sticky
– Water to the side of a graduated cylinder
• Meniscus
Cohesion
Cohesion: molecules of the same kind
stick to one another.
– Ex. The reason drops form
Organisms Depend on Cohesion
Cohesion is responsible for
the transport of the water
column in plants
Cohesion among water
molecules plays a key roll in
the transport of water against
gravity on plants
– Capillary Action
Adhesion also contributes to
capillary action as water
adheres to the wall of the
vessel.
Ex. Water in a straw
Surface Tension
A measure of the force necessary to stretch or break
the surface of a liquid, is related to cohesion
– 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.
– Is why we can “skip” rocks on water
Water Strider
Can walk on water without breaking the surface tension of water.
Specific Heat
Specific Heat is the measure of the heat that
must be absorbed or lost for one gram of a
o
substance to change its temperature by 1 C.
– A lot of heat energy required to break
hydrogen bonds, water resists temperature
change
• Most heat goes to breaking the bonds..not
much left to raise temperature
Water = high specific heat
– This is why it doesn’t usually snow in
Wilmington:
– The ocean doesn’t change temperature very
rapidly
Has a moderating effect on our weather
Density
Density: how packed together a material is
– Mass/volume
– Units: g/mL
More dense it sinks
Less dense it floats
Problem: If 60 mL of a liquid has a mass of 30g. What is
the density of the liquid?
D=30g/60mL
D=0.5 g/mL
Density of Water
Water is one of the only substances that
is less dense as a solid than as a liquid.
Prevents water from freezing from the
bottom up.
Buoyancy
The force of
buoyancy is equal to
the weight of the
fluid displaced
An object with
greater volume will
be pushed up with
more force.