WC-11: WATER MOLECULES AND TEMPERATURE
MATERIALS:
5 8OZ. CLEAR PLASTIC CUPS FOR EACH PAIR OF CHILDREN.
ONE GALLON OF ROOM TEMPERATURE WATER
ONE HALF GALLON OF HOT WATER
ENOUGH THERMOMETERS SO EACH PAIR OF CHILDREN HAS TWO
SPONGE (FOR CLEANING SPILLED WATER)
WATER TRAY
THERMOS (FOR ICE)
SPRAY BOTTLE
MATERIALS YOU NEED TO BRING FROM HOME:
BAG OF ICE
HOT WATER
COLORED PENCILS
**MAKE SURE ALL THE MATERIALS YOU NEED ARE HERE! IF THEY ARE NOT, THEN
CHECK THE EXTRA SUPPLIES IN THE BOX IN THE MATERIALS ROOM
PREPARE AT HOME:
• One 8-oz clear plastic cup is filled with water just to the top of the masking tape line and then
frozen. The other marked cup is left empty, you fill with water later in the classroom.
• Fill a glass jar to the very top with water, screw the lid on tightly, and place in a heavy plastic ziplock bag. Freeze it over night. After freezing, the lid should be bent. If the jar breaks, show the
children the broken glass still in the plastic bag.Transport the plastic cup with ice, the jar with frozen
water (still in the bag), and some ice cubes to class in the cooler.
Water Molecules & Temperature
WC – 11
page 1
WATER MOLECULES AND TEMPERATURE
WC – 11
Summer 2000
Jane Hall/ Ralph Johnson
OBJECTIVES:
To study the water molecule and the three physical phases of water and to learn about atoms and
molecules
GRADE LEVELS: 3 – 6
FOCUS WORDS:
Hydrogen, oxygen, atom, molecule, element, crystal, cohesion, adhesion, H2O
latent heat, standard atmosphere (pressure of 76 cm of mercury and 15 ° C)
BACKGROUND INFORMATION:
Heat is a form of energy and is usually measured in calories. One calorie is the quantity of heat that
will rise one gram of water one degree Celsius. (The energy in food is called calories, but those
calories are actually kilo-calories.) It is heat energy that runs our automobiles and is even responsible
for our own physical strength. The sun radiates its heat to the earth to supply the energy of life.
Temperature is a measure of the intensity of heat. It is measured in degrees Celsius. A sewing needle
that is red hot and has a temperature is 550° C contains less heat (calories) than a bucket of ice at 0°
C. Heat can be added to water without raising its temperature. This happens when ice melts and
when water vaporizes. This phenomenon is called latent heat.
When water freezes the heat given up is called the latent heat of fusion. It requires 80 calories to
freeze/or thaw one gram of water.
When water boils we have the latent heat of vaporization, and it takes 539 calories to vaporize one
gram of water at standard pressure. When it condenses it gives back that 539 calories.
Water cannot change state, from ice to liquid or from liquid to vapor, without the addition or
removal of heat. When steam condenses to water, and when water freezes to ice, the heat is given
back. While water is boiling on the stove and the burner is on full, the water will remain at 100° C
until it is ALL evaporated. When ice is melting in a pan on the stove the temperature will remain at
0° C until ALL the ice is melted.
If you could take a drop of water and divide it up until you have the smallest possible water particle,
you would have one molecule of water. If you continue to break the molecule into smaller pieces it
would no longer be water. You would end up with 2 pieces of hydrogen and 1 piece of oxygen.
These pieces are called atoms. Now, if you put the two pieces or hydrogen and one piece of oxygen
back together again, you have your water molecule back. Of course, we cannot do this experiment
because a molecule is so small it would take millions and millions of them to make a drop big
enough to see. Water is a molecule, made up by the mutual attraction of three atoms; two atoms of
hydrogen and one of oxygen. (Chemically it is written as H2O.)
Water Molecules & Temperature
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Water is our natural air conditioner. It stores heat in the summer and releases it in the winter (latent
heat). Frozen water, ice, floats on liquid water. A layer of ice on the water's surface is a good heat
insulator. It tends to trap the heat in the water below it. If this did not happen the entire supply of
water would freeze to the bottom of the ocean, and there could be no life on earth.
The ocean is our reservoir of the earth's most precious commodity, water. Water moves from the
ocean to land through the air. There it falls as rain to nourish all terrestrial life. Heat from the sun
warms the oceans. When the surface becomes warm enough the energy from the sun evaporates the
water into a vapor where it rises into the air and is carried over land by the wind. The vapor rises,
and as it does it chills and gives up its latent heat. The rain supplies the flowing streams and rivers,
and fills lakes.
The most common state of water is the liquid state. Liquid water is held together by the mutual
attraction of its molecules. This attraction is called cohesion. Each molecule of water in the liquid
state is free to move around freely; this is true of molecules in any liquid. In their random motion the
molecules bump into each other and knock each other around. As water is heated, the molecules
move faster, and thus bump harder. Those molecules near the surface might be knocked so hard that
they are knocked right out of the water and into the air. There they float freely, and move with the
wind.
As the temperature rises more, the molecules bump so hard that they overcome their cohesion and
separate into bubbles of vapor (steam) which rises to the surface and escapes into the air. When
water molecules are in the air, they are in a gaseous state and they mix with all the other gasses in the
atmosphere.
As the vapor cools the molecules can again cohere to form drops. When the drops get big enough
they fall back to the earth as rain. While they are growing into rain drops we can see them as clouds.
BACKGROUND INFORMATION:(continued)
On the earth's surface if the temperature continues to drop, the movement of water molecules in the
liquid state move slower and get closer together. In a body of water the cooler water becomes more
dense and sinks to the bottom allowing the warmer, less dense water to rise to the surface. When all
of the liquid water in an area has reached the same cold temperature. and heat is still being lost, the
molecules will start to lock themselves into crystals of ice. In doing this they spread apart and are
less dense than the liquid. They then float to the surface to form a layer of ice. When the ice gets
thick enough we can go skating on the surface, and the fish under the ice can continue to swim.
Water Molecules & Temperature
WC – 11
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THREE PHASES OF WATER — VAPOR, LIQUID & ICE
H
Hydrogen ( H2)
H
Oxygen (O2)
O
Water (H2 O)
Other molecules
in the air
Water vapor in the air shown in this balloon
Water surface
Interlocking Crystals
of Ice
Water molecules escaping cup
by evaporation
Water molecules in a cup
Notice that the molecules as shown here area million or more times larger than they actually are.
Water Molecules & Temperature
WC – 11
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ACTIVITIES:
TIME REQUIRED: 20 minutes
Water is everywhere. It is in our oceans, our lakes and streams, in the polar ice caps and mountain
glacier, and it is in the air. Water is a liquid, it is a solid, and it is a gas (called vapor) depending on
its temperature. Can you imagine how water looks if you could see its smallest form? How small can
water get and you can still see it? What if we could pretend that you could see the smallest form of
water – a molecule – how would that look?
ASK:
RESPONSE:
What is an element?
An element is a substance which cannot be broken up into a substance
different from itself. It is made up of one type of atom only.
ASK:
What is an atom?
RESPONSE:
An atom is the smallest whole particle of matter that you can have.
ASK:
What is an element?
RESPONSE:
An element is a substance that consists of only one type of atom.
ASK:
What is a molecule?
RESPONSE:
When atoms of different types are attracted together to form a substance,
different from the element of any of those atoms, the smallest particle of that
substance is a molecule.
ASK:
What is water?
RESPONSE:
Oxygen is an element and so is hydrogen. Each are gasses in their natural
state. When these two elements combine, by the oxygen atom attracting two
hydrogen atoms, they form one molecule of water.
EXPLAIN:
Scientists have shorthand ways of identifying chemical substances. They
identify water with the symbol "H2O." This symbol says that there are 2
hydrogen atoms (H2) with 1 oxygen atom (O) to form 1 molecule of water,
H2O.
SHOW
The models of water molecules. Can the children figure out how many atoms
of hydrogen and oxygen make up the molecule? Are the molecules attracted to
eachother?
COLOR THE MOLECULE EXERCISE CAN BE USED WITH YOUNG CHILDREN (3RD ):
DO:
Give each child a copy of the "Color the Water Molecule" sheet. Also give
them each one blue and one yellow crayon
DO:
Have the children color the two hydrogen atoms, in the upper diagram on the
right hand side, yellow, and the oxygen atom blue.
EXPLAIN:
The two hydrogen atoms have not yet combined with the oxygen atom.
DO:
Have the children color the two hydrogen atoms in the bottom diagram
yellow, and then color the entire molecule blue.
EXPLAIN:
The three atoms have now joined to form a molecule of water. The change of
color of the hydrogen atoms from yellow to green indicates that they are no
longer free atoms, but are now a part of the water molecule.
ASK:
Water's natural state is liquid; what is a liquid?
RESPONSE:
A substance that is neither solid nor gaseous. See the diagram of "Water in a
Cup”
ASK:
What keeps the molecules in the cup?
RESPONSE:
The mutual attraction of each molecule to all of its neighbors.
ASK:
Can the molecules move around among the other molecules in the liquid?
RESPONSE:
Yes. That is what makes a liquid flow.
Water Molecules & Temperature
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ASK:
What is steam?
Steam is water in a gaseous form, also called water vapor.
What is a gas?
A gas is a substance that will fill the whole container no matter how little or
how much of the substance there is. See the diagram of the balloon filled with
gasses.
Do the molecules in steam have an attraction for each other?
Yes.
Then why do they not gather together into a liquid?
Because they have too much heat energy. They bump together so hard that
they bounce apart.
What happens when the molecules of a water vapor lose some of their
energy?
Their mutual attraction can bring them together to form drops of liquid water.
What happens when those drops get big enough?
It rains.
What is a solid?
A solid is a piece of matter that does not need a container to hold it together.
Remove some ice from the cooler, place on a tray or paper towel
Is ice a solid?
Yes.
Is ice water?
Yes. It is water in the solid state.
What is a crystal?
A group of molecules that lock themselves together in some geometric form.
See the diagram of crystals of water.
Why does ice float in liquid water? Ask a child to place some ice in a cup of
water.
When water forms into the crystal, ice, the molecule must spread apart. This
makes the ice less dense than the liquid water. A level container of ice weighs
less than the same size level container of liquid water, so it must float.
Take the plastic cup of ice with the masking tape band around it to display to
the class. Have the other plastic cup (with masking tape) filled to the top of the
masking tape with liquid water.
Last night I filled this just to the top of the masking tape, then I put it in my
freezer until I put it in the cooler to bring to class.
Does the cup seem fuller now? Compare to the cup with liquid water.
The molecules of ice are farther apart than they were when it was water.
What would happen if I filled a glass jar full of water, screwed the lid on
tight, and then put it in the freezer until it was frozen solid?
The ice would take up more space in the jar, probably causing the top to bend
to make more room for itself. If it could not find enough space by bending the
lid, it could break the glass.
Take the plastic bag containing the glass jar out of the cooler and have the
children examine it. Even if the jar is not broken, do not remove it from the
bag.
Why is the jar in the bag?
To catch the glass if it breaks.
Why do I not take the unbroken jar out of the bag?
Water Molecules & Temperature
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RESPONSE:
ASK:
RESPONSE:
ASK:
Because the glass is under a heavy strain by the expanding ice, and it might
break with handling.
What would happen if a rock on a mountain had a crack in it that was full
of water and then the weather got so cold that the water froze?
The freezing ice would have enough strength to break the rock. This is a part
of the erosion process that wears down the mountains.
What would happen if ice was not lighter than liquid water, but heavier?
Imagine ice cubes, icebergs, ice on top of ponds, lakes or streams.
MAKE SURE TO PUT THE JAR OF ICE WITH LID AND ICE IN CUP WITH MASKING
TAPE BACK IN THE COOLER IMMEDIATELY AFTER SHOWING THEM. THIS WILL
ENSURE THAT THEY STAY FROZEN BETWEEN GROUP ROTATIONS.
Water Molecules & Temperature
WC – 11
page 7
COLOR THE WAT ER MOLECULE
HYDROGEN
HYDROGEN
OXYGEN
MOLECULE OF WATER
( H 2 O)
H
H
Color the hydrogen
atoms yellow and the
oxygen atoms blue
( H 2 O)
Color the 2 hydrogen atoms yellow, then color all 3 atoms
blue. The resulting green represents how the combining of
the 3 atoms results in a molecule that is not oxygen or
hydrogen, but a different substance, water.
Water Molecules & Temperature
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