Notes: The Water Cycle and
Unique Properties of Water
1/13/15
How much water is there?
• Water covers most of the Earth.
– There are 4 oceans: Atlantic, Pacific, Indian, and
Arctic. They are all connected to each other to
form one huge ocean. Any part of this ocean is
called the sea.
• ~71% of Earth’s surface is covered with water.
Most of the oceans are in the Southern
Hemisphere.
What is the difference between salt
and fresh water?
• Fresh Water vs. Salt Water
– Fresh water: not salty, has little to no taste, color,
or smell.
• Ex. Most rivers and lakes
• Important for life on Earth
• Scarce (rare): only 3% of water on Earth
– Of this, 30% is free flowing (underground or in
rivers, lakes, atmosphere, and living things), while
70% is frozen.
Fresh water vs. Saltwater (cont.)
• Salt water: water that has dissolved salts & other
minerals.
– Ex. Oceans
– 97% of water on Earth
– Salinity: how much salt is dissolved in water (how
salty the water is). The average salinity of the ocean is
35 parts per thousand (35 salt molecules for every
1000 molecules of water).
– Salinity increases when water evaporates or freezes
(salt does not evaporate or freeze, so the salt is left
behind!). Salinity decreases when ice melts into the
ocean or it rains.
What is the Water Cycle?
• The water cycle: the continuous movement of
water through the environment
– Total amount of water on earth does not change.
– 3 major processes:
•Evaporation
•Condensation
•Precipitation
Evaporation
• Evaporation: water changing from a liquid to
a gas
– Requires heat (from the sun, stove)—gets
WARMER
– 85% of evaporation occurs from the ocean (salt
doesn’t evaporate)
– Ex: water boiling, sidewalk drying
Condensation
• Condensation: water changing from a gas to
a liquid
– occurs as air cools, forms clouds
– Cold air dissolves less water vapor than warm air,
so the vapor condenses into droplets of liquid
water to form clouds. Clouds are visible evidence
of water in the atmosphere.
Precipitation
• Precipitation: any form of water that falls
from clouds
– Water reaches land →sinks into the soil or flows
into streams and rivers (called runoff).
– All precipitation is fresh water (the salt does not
evaporate from the ocean).
– The force of gravity pulls the flowing water
downward, and usually it eventually ends up in
the ocean.
Draw the Water Cycle
Draw the Water Cycle
How is water unique?
• Water is a unique substance.
– allows life to live on Earth
• exists in three phases:
–solid
–liquid
–gas on Earth
What is polarity?
• Polarity: A polar molecule is a molecule that
has positive (+) and negative (-) regions.
– These regions allow it to become attracted to
many other types of molecules.
• In polar molecules, electrons are not
distributed equally, which causes the
molecule to bend and makes water polar.
Polarity
What is the difference between
cohesion and adhesion?
• Cohesion: ability of water molecules to stick to
each other.
– Water molecules want to “stick together” like
magnets because of its positive (+) and negative (-)
regions (opposite charges attract).
– Polarity causes attraction between molecules
– Causes surface tension—attraction between
molecules at the surface; makes water bead up into
drops and allows light objects to sit on top of the
water. Water has high surface tension.
• Adhesion: The ability of water to stick to other
substances
What is the density of water?
• Density = mass/volume (g/mL or g/cm3)
• Objects sink or float in water because of
density
• Density of water = 1 g/mL
• Density less than water (1) = floats (less
dense)
• Density greater than water (1) = sinks (more
dense)
What is buoyancy?
• Buoyancy: Force that pushes
up on an object in fluid
• Related to density: the lower
the density = the more
buoyant the object
What is turbidity?
• Turbidity is the measure of the clarity of the
water (how clear the water is).
– More solids in water = high turbidity = murky or
muddy water
– Less solids in water = low turbidity = clear water
• To increase turbidity: add lots of fine
sediments (silt, clay, etc)
Turbidity
What is specific heat?
• Specific Heat: the amount of energy needed
to raise the temperature of 1g of any
substance 1ºC
– Water has a HIGH specific heat
• Takes A LOT of energy to heat water
• When water cools off, A LOT of heat is released
• Oceans/Lakes stay warmer longer in winter,
even if temperature decreases; it takes longer
to heat them up in summer
Why is water called the universal
solvent?
1.A solvent is a liquid capable of dissolving
another substance.
2.Water is capable of dissolving a lot of different
substances, which is why it is called the
universal solvent.
3.Water dissolves more substances than any
other liquid!
4.Water’s polarity is one of its characteristics
that makes it the universal solvent.