Properties of Water
reflect
Water is found in many places on Earth. In fact,
about 70% of Earth is covered in water. Think about
places where you have seen water. Oceans, lakes,
and rivers hold much of Earth’s water. Some water is
trapped in glaciers and icebergs. Even the air holds
water! If you have ever been outside on a foggy day,
you have seen water in the air. Fog is an example of
water that forms from a gas called water vapor. Even
on clear, sunny days, there is water vapor in the air.
Water is found in different physical forms, or states,
and it can change between these states. Water can change
from a solid to a liquid. It can change from a liquid to a gas.
Water can even change from a gas to a liquid. But how, exactly,
does water change between its different states?
states: classifications
of matter as a solid,
liquid or gas.
What are some properties of water? Can these properties change? How?
Pure water is an amazing substance. It can exist naturally as a solid, liquid, or gas. When
enough heat is added to or taken away from water, it will change its physical state. For
example, water sometimes collects in puddles during a rainstorm. With enough heat from
the Sun, the water will eventually change from a liquid (in the puddle) to a gas (water vapor
in the air). This is an example of evaporation. Then the gas, or water vapor, can change
again. If it cools enough in the air, water vapor will change into a liquid and fall back to
Earth as rain. Changing from a gas to a liquid is called condensation.
look out!
When a substance warms up, it gains heat. But what happens when a substance cools? A
cooling substance loses heat—it does not gain cold. Think about an ice cube tray. You can
fill it with water and put it in the freezer to make ice. As the water changes from a liquid to a
solid, it loses heat.
what do you think?
Look at the photographs
below. The picture on the left
shows water changing from
a liquid to a gas. The picture
on the right shows water that
has changed from a liquid
to a solid. What caused the
physical state of each water
sample to change?
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Properties of Water
Discover Science: Water on Mars?
Is there water on other planets? As far as
we know, Earth is the only planet in our s­ olar
system containing liquid water. But scientists
wondered for many years w
­ hether other planets
had moving water at one time. Recently, they
found exciting evidence to suggest water once
flowed on Mars. When water flows over rocks
for a long time, the rocks break down and
­become smooth. On Mars, some rocks look like
they were smoothed by water long ago.
Scientists are not sure what happened
to the water. But, because matter cannot
disappear, the water most likely evaporated
or froze. (Large ice caps are visible at each
pole on Mars.) Scientists also think water
may be buried beneath the planet’s surface.
This image compares rocks found on
Mars (left) with rocks on Earth (right).
Both sets of rocks look like they were
smoothed by flowing water.
Which tool can we use to measure different
­temperatures?
Losing or gaining heat causes the temperature
of a substance to change. If water loses heat, the
water’s temperature decreases. Similarly, if water
gains heat, the water’s temperature increases.
temperature: a
measure of th average
energy of motion in the
particles of a substance.
Temperature is measured in units called degrees.
The most common tool for measuring temperature
is a thermometer. Sometimes temperature is
measured on the Fahrenheit scale. When
you hear a weather report, you might hear the
temperature will be 65 degrees Fahrenheit, or
65°F. However, scientists use the Celsius scale to
measure and record the temperatures of different
substances. A temperature of 65°F equals about
18 degrees on the Celsius scale (18°C).
Fahrenheit:
temperature scale
commonly used in the
United States.
Celsius: temperature
scale used by
scientists. On this
scale, water freezes at
0° and boils at 100°.
try now
Take a little time to explore how to measure temperature on the Celsius scale. Remember
that many thermometers are made with glass, so handle yours carefully.
1.To complete this activity, you will need the following materials:
• Celsius thermometer
• A container of room temperature water, about one cup
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Properties of Water
• Four or five ice cubes
• A spoon
2.Place the thermometer in the container of water. Wait for about 1 minute.
3.With the thermometer in the water, note where the liquid on the thermometer stops along
the number line. This is the water temperature. Record it in degrees Celsius, or °C.
4.Take the thermometer out of the water. Add the ice cubes and stir with the spoon.
5.Repeat Steps 2 and 3.
6.Think about how the temperature would change if you added heat. Would it increase
or decrease?
At what temperatures on the Celsius scale will water freeze or boil? At what
­temperature will ice melt?
Like other substances, water needs to reach a certain temperature in order for its physical
state to change. The temperature at which a substance changes from a liquid to a gas is
called its boiling point. The temperature at which a substance changes from a liquid to a
solid is called its freezing point. As you might have guessed, the temperature at which a
substance changes from a solid to a liquid is called its melting point.
All substances have specific boiling, melting, and freezing points. For example, the boiling
point of pure water is 100°C. You can place water in a pot and heat it on the stove. Once
the water temperature reaches 100°C, it will begin to boil. This boiling point does not
change whether you have a large pot of water or a small droplet of water. Boiling, melting,
and freezing points are constant, meaning they do not change unless the substance itself
is changed. If you add salt to water, you are changing pure water into a different substance.
This new substance will have a different boiling point.
Melting and freezing are reverse processes. Because of this, the melting point and freezing
point of water are the same. They are both 0°C!
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9
Properties of Water
What do you know?
Water has constant boiling, melting, and freezing points that cause its physical state to
change. Color each thermometer in the chart below to show how the water’s temperature
changes in each example. Then, read the descriptions of changes in physical state. Decide
which change matches each example. Write your answers in the final row of the chart.
For each example, color the thermometer on the left to show the water’s ­starting
temperature. Color the thermometer on the right to show the water’s ending temperature.
Water starts at 60°C and is
Water starts at 40°C and is
Water starts at –10°C and is
heated until it boils.
cooled until it freezes.
heated until it melts.
The water changes from:
The water changes from:
The water changes from:
Changes in Physical State
solid to liquid
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liquid to solid
liquid to gas
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Properties of Water
connecting with your child
Properties of Water at Home
To help students learn more about the
properties of water, set up an experiment
to compare the time it takes to boil different
quantities of pure water. You will need the
following materials to get started:
•Eight cups of water set to room
temperature
•Measuring cup
•Hot plate or access to stove burner
•Small pot
•Timer or stopwatch
•Heat-resistant Celsius thermometer that
measures at least 120°C (optional)
Remind students to use extreme caution
when using the hot plate or stove burner.
In order to bring the water to room
temperature, let it sit in a room for about an
hour before the experiment.
Set up the experiment by adding two cups
of room temperature water to the pot. If
possible, have students measure and record
the water’s temperature. Next, carefully
place the pot on the hot plate or stove and
start the timer. As soon as the water begins
to boil, record the elapsed time. If possible,
have students carefully measure and record
the water’s temperature. (Measurements
should confirm that water boils at 100°C.)
Turn off the burner and pour out the water.
Rinse the pot with cold water and drain.
Now, add one cup of water to the pot.
Repeat the experiment by measuring the
temperature of the water, placing the pot on
the burner (be sure to use the same setting
on the burner), and recording the amount
of time it takes for the water to boil. Repeat
these steps for the following quantities of
water: one-half cup and four cups. Compare
the results from each trial.
If time allows, try a similar experiment with
salt water. Simply add a quarter-cup of
salt to a cup of water and stir until the salt
is dissolved. Record the amount of time it
takes the salt water to boil, and compare
this to the pure water results.
Here are some questions to discuss with
students:
•Did the amount of water affect the
amount of time it took for the water to
boil?
•Did the amount of water affect the
boiling point? If you were not able to
obtain boiling point measurements, think
about what you observed during the
experiment.
•Suppose you added salt to the water.
How do you think this would affect the
boiling point? Do you think it would affect
the boiling time?
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