wind turbine kit,
blood type test,
Liquid Density & Lava Lamps
In this issue:
- Homemade Lava Lamp
- Rainbow Density Column
- Fabulous Facts
- Science Links
Homemade Lava Lamp
You know the mesmerizing feel of watching a lava lamp, with its large colored
bubbles sinking and rising and morphing. With this project, you can make your
own (temporary) lava lamp with household materials! It's easy and safe, and it
looks very cool.
>> Check out our project video to see the homemade lava lamp in action!
What to do:
- Fill the flask most of the way with vegetable oil.
- Fill the rest of the flask with water. The water will sink to the bottom
under the oil.
- Add a few drops of food coloring; your choice of color. The food
coloring is water-based, so it will also sink and color the water that is
now at the bottom of the flask.
- Break an alka-seltzer tablet into a few small pieces, and drop them in
the flask one at a time.
- Watch your lava lamp erupt into activity! As the reaction slows down,
simply add more alka-seltzer.
A lava lamp works because of two different scientific principles, density and
- Density is the measurement of how compact a substance is - how
much of it fits in a certain amount of space. (The scientific equation is
density = mass/volume.) If you measure an equal volume of oil and water,
you'll find that the water is heavier than the same amount of oil. This is
because water molecules are packed more tightly and a cup of water actually
has more mass than a cup of oil. Because water is more dense than oil, it
will sink to the bottom when the two are put in the same container. Density
is affected by temperature—the hotter a liquid is, the less dense it will
- Even though they have different densities, oil and water would eventually
mix together if it weren't for polarity. Water molecules
are "polar" because they have a lopsided electrical charge that attracts
other atoms. The end of the molecule with the two hydrogen atoms is
positively charged. The other end, with the oxygen, is negatively charged.
Just like in a magnet, where north poles are attracted to south poles
("opposites attract"), the positive end of the water molecule will connect
with the negative end of other molecules. Oil molecules, however, are
non-polar— they don't have a positive or negative charge, so they are not
attracted to the water molecules at all. This is why oil and water don't mix!
Real lava lamps use a polar and non-polar liquid just like our homemade one
did. In a real one, however, the densities of the liquids are much closer
together than vegetable oil and water. The denser liquid sinks to the bottom,
but the lava lamp light heats it up until it expands and becomes less dense,
causing it to rise upward. As it gets farther from the light, it cools down,
becoming more dense again until it sinks; then the cycle starts all over.
Instead of using a light, in our homemade lava lamp we used alka-seltzer to
power the lamp. The alka-seltzer reacts with the water to produce carbon dioxide
gas bubbles. These stick to the water droplets. The water/gas combo is less
dense than the oil, so they rise to the top of the flask. At the top, the gas
bubbles pop and escape into the air, allowing the dense water to sink back to
the bottom again.
Lava lamps powered by heat are trickier to make and can use more hazardous
materials. You can experiment fairly safely with things like rubbing alcohol and
mineral oil or lamp oil. See if you can make a lamp powered by heat!
Fun Chemistry Kits
A chemistry kit provides a host of fun projects right at your fingertips!
Make color-changing reactions, fizzing solutions, and much more. Explore with
the Chem C1000, Chemistry Fun Experiment Kit, or topical chemistry sets like
Chemistry of Food.
Rainbow Density Column
Using a knowledge of liquid density, you can easily "stack" several liquids
on top of each other! Use food coloring to make a rainbow of colors.
- Liquids of different densities: honey, corn syrup, dish soap, water,
vegetable oil, rubbing alcohol
Graduated cylinder or tall glass or jar
- Food coloring
What to do:
- Pour an inch (or however much you want) of honey into the bottom of the
cylinder or glass.
- Use food coloring to color a little bit of corn syrup (if it's the light
kind; just leave it brown if it's the dark kind). Slowly and carefully pour
an inch of the corn syrup on top of the honey.
- Color some liquid dish soap and carefully add an inch on top of the corn
syrup. You may find it easier to use a pipet for this one instead of
- Next, use a pipet to add an inch of colored water on top of the dish soap.
- You won't be able to color the vegetable oil, because food coloring is
water-based and water and oil don't mix! Go ahead and add an inch of oil on
top of the water.
- Finish it off with an inch of colored rubbing alcohol. (If you have lamp
oil, you could also add that to the very top.)
- Voila - a beautiful rainbow of stacked liquids!
Each of the liquids you used had a different density. You added them
to the cylinder in order of most dense (honey) to least dense (rubbing alcohol).
Since each new liquid was less dense than the one before it, it floated on top
instead of mixing together. You can try other liquids, if you want to! To figure
out where your new liquid would fit in the column, you can measure the density
of all the liquids. Measure an exactly equal volume of each liquid and weigh it
(be sure to subtract the weight of the container). Even though the amount of
liquid is the same, the denser ones will be heavier. (Density = mass/volume.)
There are many different things that affect density, such as temperature.
Heat causes substances to expand and become less dense, while cold causes them
to contract and become more dense. (One exception is water - it becomes more
dense with cold until the freezing point, but it freezes in a crystalline
structure that makes ice less dense than liquid water.) Adding things to a
liquid will also change its density. For example, salt water is more dense than
regular water (which is why it's easier to float in salt water than in fresh
water!). You can try building a density column using only colored water. Try
stacking hot, cold, and room temperature water, or try building a column with
salt water, sugar water, and fresh water.
More Fun Projects:
Forget the life jacket. The Dead Sea contains the saltiest water on
earth, which is also the densest water found naturally on earth! You don't need
flotation devices if you are swimming in the Dead Sea. Your body's density is
already much less than the water's, so the only thing you can do is float higher
than you ever would in fresh water!
Freeze and float. Most liquids contract when they freeze, making them
more dense in their solid form than in their liquid form. (They have the same
mass, but it's packed into a smaller volume.) Water does the opposite: it
expands as it freezes, lowering the density. Since ice is less dense than water,
it floats. And it's a good thing it does! If water acted like most other
liquids, lakes and rivers would freeze solid and all life in them would die.
Instead, a layer of ice forms on the surface, leaving liquid water underneath.
Thermometers work because of the relation between liquid density and
temperature! Learn more and how to make your own at
Hot air balloons also work because of density! Check out
how they work.