BACKGROUND:
The Water Cycle explains interactions
between the atmosphere, hydrosphere, and lithosphere. Evaporation
of water from the oceans, seas, rivers, and streams into the atmosphere
produces precipitation.
Water is a transparent, odorless, tasteless
liquid composed of the elements hydrogen and oxygen. It is a very good
solvent, meaning that many substances can dissolve in it easily.
Water is important to our lives, and without it we could not live.
In fact, there are no living creatures that can live without water.
Water most probably originated on this planet as gases were being emitted
from volcanoes. The Earth's atmosphere captured this water and has
continuously recycled it throughout time, in what is called the water cycle.
Water evaporates and forms clouds; the clouds provide rain and snow, which
is collected in rivers, lakes, underground reservoirs, and oceans that
are the source for further evaporation. Water is that perfect substance
for the water cycle, because it has a high boiling point and a low freezing
point.
Water's surface tension (the ability of a
substance to stick to itself) makes it an excellent substance to float
heavy objects upon. Water not only sticks to itself, but also to
other surfaces, and this allows it to move against gravity, which is very
important to plants when transporting water form the soil to their leaves.
This upward motion is known as capillarity or capillary movement.
PROCEDURE:
Students in this lab will experience
bubbles from different liquids. This is a fun lab for students, but
we recommend that you do this activity outside and maybe just before the
students go home. Just in case students get a little damp!
- Each pair of students receives one
bubble trumpet or any other instrument that can produce bubbles.
Straws also make excellent bubble makers! (We suggest straws if you have
to do this activity inside.)
- Have three buckets, each with a different
bubble solution. Students will test different types of solutions,
to see which one produces the best bubbles. You should pre-mix the
solutions. You may want to put different food coloring in the unknowns
for students to easily identify each mixture. We suggest the following
mixtures:
unknown
#1 = bucket of plain water
unknown
#2 = dishwashing liquid + water (equal parts)
unknown
#3 = dishwashing liquid + water + a little salt and sugar
- Before you have the students test
the mixtures, we suggest you go over how to make a bubble, especially if
you are using bubble trumpets. Hold the trumpet about 2 cm
away from lips and direct a small stream of air into the mouthpiece.
You are forcing the air from your mouth into the trumpet creating a suction
that pulls surrounding air along with it into the trumpet. They do
not need to put their mouth on the trumpet, and they do not have to blow
hard.
- Students will discover that plain
water does not make bubbles. Plain water has too much surface tension,
so it cannot form a bubble. Soap tends to work its way in between
the water molecules on the surface of the bubble (between Mickey Mouses
ears), thus reducing surface tension and allowing the outside film of water
to stretch out, creating a bubble. Remember also that a bubble has
two surfaces, inside of the bubble and the outside. This is
called a film. Understanding a bubble is more complicated than this,
but students in the second grade just have to see the results of varying
surface tension. As they will see that not all soapy liquids are
the same.
- Students should experiment with the
different mixtures to find out which mixture will make the better bubble.
The mixture with dishwashing detergent and salt and sugar should be superior.
You may have to experiment yourself with the mixture before you let the
students at them. Instead of the above mixtures you may want to compare
brands of dishwashing solutions. Which one makes the best bubbles?
