Young Scientist Program Chemistry Teaching Team
States of Matter: Liquids and Gases
We are going to do two experiments to help us understand the behaviors of liquids and
gases better today.
1. Balloon volume changes in liquid N2 and warm water
2. Liquid Rainbow
Introduction
The world around us is composed of physical matter in four basic states: solid, liquid,
gas, and one that is rarely encountered outside a physics lab, plasma.
By addition or subtraction of energy, we can change the states of matter. You have
already encountered several of these processes in everyday life:
When a solid changes into a liquid, it is often called melting.
When a liquid changes into a solid, it is often called freezing.
When a liquid changes into a gas, it is often called boiling.
When a gas changes into a liquid, it is often called condensation.
In all of these scenarios, energy is either added or released to induce a state change in the
matter.
An Exercise
Have the students assemble in a large space between the demonstration tables.
Tell them they are all currently small molecules in the solid state, such as water
molecules, and that they must stand still in a rigid shape (let’s say a rectangle). Tell them
that you, the experimenter “outside the sytem”, are increasing the temperature. You may
take a minute to ask them how exactly one could add energy to a system.
As it gets hotter, the “molecules” have more energy and move faster. When a
sufficient amount of energy has been added, the water molecules are moving too
vigorously to be a solid, and the transition from solid to liquid occurs. Point out that the
more vigorously the “molecules” move, the more space they require.
Young Scientist Program Chemistry Teaching Team
Explain that in general, addition of energy to a group of molecules increases the
molecules’ kinetic energy, which is expended as random molecular movement, which in
turn requires more space for any given number of molecules. Once the molecules’ kinetic
energy reaches a certain threshold, a state change occurs.
Experiment 1: Balloon volume changes in liquid N2 and in warm water
How do temperature changes affect the kinetic energy of air molecules? In this
demonstration balloons are dipped into liquid nitrogen and warm water to see how their
volumes (and pressures) change.
Materials
Balloons blown up to ~2/3 max volume
1-liter beaker
hot plate
liquid nitrogen and container in cylindrical Rubbermaid container
Tongs or forceps for dipping balloons into liquid nitrogen
Goggles
Gloves
Safety
Keep water warm but not scalding hot. Warn students against resting their hands
on the hot plate. Warn students to be careful with liquid nitrogen and DO NOT touch it to
their skin. Note that liquid nitrogen is very cold (-196C). Wearing goggles when
working with liquid nitrogen is required.
Procedure
Wear glasses and gloves when handling liquid nitrogen!
1. Fill the beaker about halfway with warm tap water and place on the hot plate to keep it
warm.
2. Place three balloons on the table to show that they are of equal size.
Before dipping the balloon into the liquid nitrogen, ask the students what they
think will happen to the balloon. Will it shrink? Will it expand? Will it break?
3. Have a student (properly outfitted with goggles and gloves) dip one of the balloons
into the liquid nitrogen and place it next to the other balloons. It will have shrunk
considerably but will quickly regain its size as it warms to room temperature. Talk about
kinetic molecular theory (that all molecules are always moving to some extent and that
they move faster at higher temperatures, slower at lower temperatures) and what this
means for the air molecules inside the balloon.
Young Scientist Program Chemistry Teaching Team
4. After discussing predictions of what will happen, have a student dip a balloon into the
beaker of warm water and discuss what happens. If time allows, all of the students who
want to shrink and expand a balloon may do so.
Questions
1. After being dipped into the liquid nitrogen, how fast do you think the air molecules
inside the balloon are moving?
The dramatic cooling of the air molecules with liquid N2 would slow the air
molecules down to much slower than they would move at room temperature.
2. Compared to (1), how fast do you think the air molecules inside the balloon are
moving after being dipped into the warm water?
Warming the air molecules with warm water would increase their speed relative
to room temperature, and certainly would be much faster than the molecules
could move after liquid N2.
3. When the air molecules are moving faster, what does this do to the volume of the
balloon?
The quick movement of the air molecules increases the volume of the balloon.
4. What are the quickly moving air molecules doing to change the volume of the balloon?
Increasing the speed of the air molecules (with warm water) increases the
pressure that the molecules exert on the walls of the balloon. Because the balloon
is pliable, it increases in volume to reduce the pressure exerted by the air
molecules.
Experiment 2: The Liquid Rainbow
Density is defined as mass per unit volume. We are going to determine the densities of
several solutions.
Materials
Four 500 mL bottles of solutions tinted with food coloring:
Water
10% glycerol
20% glycerol
30% glycerol
test tubes & racks
transparent straws
Young Scientist Program Chemistry Teaching Team
balance
vials containing known volumes of liquids
Methods
By dipping a transparent straw into a solution and withdrawing it with a finger capping
the top, the students can draw liquid into the straw. They can draw a second liquid into
the same straw by dipping the straw deeper into the second liquid than the first and
withdrawing it as before.
If the second liquid is denser than the first, the first will float on top and two distinct
bands will be visible in the straw.
If the second liquid is less dense than the first, the two liquids will mix as the second
liquid floats upward, mixing the two colors.
Find the relative densities of the liquids by trial and error. When you have four distinct
bands in the straw, you will have determined the order of density from least dense on top
to most dense on the bottom.
Questions
Density = amount of matter in a given amount of space
= mass per unit of volume
D = mass
volume
What is the order of densities of the four solutions, from least dense to most dense?
How do you think a temperature change would affect the density of a solution?
We can confirm the liquids’ densities if we measure the mass of a known volume of each
liquid.
color
clear
red
yellow
blue
mass of liquid
mass of
and tube (grams) tube (grams)
mass of
liquid (grams)
volume of
liquid (mL)
density of
liquid (grams/mL)
Young Scientist Program Chemistry Teaching Team