Teaching Density to Elementary Students: Lesson Plans for Building Lava Lamps Using Materials Found at Home

The craft-store franchise AC Moore went out of business just before the Covid Quarantine was imposed.  A large AC Moore store was situated across the parking lot from my ten-year-old’s weekly guitar lessons, and we made it a point to peruse the place for big bargains each time the sign out front advertised another drop in prices. One of the prizes among the windfall we brought home - you’d be amazed at the non-craft stuff they were moving - was a do-it-yourself lava lamp kit. My son followed the first of several recipes provided with the kit and, with the help of his teenage brother, created a lava lamp that garnered the admiration of everyone in the family that evening.

The directions were simple enough and generally called for ingredients that are readily available in most kitchens. As a result, I decided to make 'layered lava lamps' with the children in our partner homeschool, to introduce a lesson about density.

Knowing the other two kids would not be happy that my son would get to keep the lava lamp included with the kit, I found 3 small cylindrical spice jars and rinsed them out so that everyone could build and take home their own identical lava lamp. (Any small (think travel size), cylindrical glass or plastic jar will do - honey, olives, salad dressing, olive oil, mayonnaise, etc - as long as it’s clear and not colored.)

Of course, no lava lamp is complete without a light at the base to illuminate the layers and/or bubbles created. Before Covid hit, I was scheduled to set up and oversee a table at the UNC Science Expo, where participants would learn about electricity by creating their own light-up cards. Of course, the festival was canceled, which left me with heaps of button batteries and tiny light-emitting diodes - perfect for creating the lava-lamp base lighting we required. 

I set each of the jars, lids on, in front of a different seat at our kitchen table, along with one battery and one LED per jar. Then I set a roll of scotch tape and the following ingredients in the center of the table:

* liquid dish detergent (best if colored)

* food coloring (preferably 2 different colors that are also different from the dish detergent)

* vegetable oil

* rubbing alcohol

[+ spice jars with lids, button batteries, light-emitting diodes (LEDs), and clear sticky tape]

That afternoon, following the instructions below (in order), I helped each child build their own layered lava lamp while the other two watched:

1. Using their fingers, each child held one of the wires protruding from their LED to the bottom of the button battery and the other LED wire to the top of the button battery. If the light didn’t immediately illuminate, they reversed the connections. (If the light still didn’t illuminate, I gave them a new LED.)

2. Once the light illuminated, we taped the LED connections to the battery, then taped the battery to the bottom of the spice jar. (It is important to do this step first, because your tape won’t stick to the glass if it gets wet or oily. If the bottom of your glass jar is not inverted, you can envelope the taped battery-LED pair in clay or play dough (be creative) until your lava lamp sits upright without leaning.)

3. Next, using a measuring cup with a spout, we measured ~1/4 cup of water and mixed in a drop or two of food coloring (a different color than the dish detergent), Then we poured the water into the spice jar until it the jar was filled 2/5 of the way. We poured the water slowly, so that it flowed down the side of the jar and formed a layer on top of the dish detergent. (If you pour the water too fast, it can mix with the dish detergent and ruin your results.)

4. Next we measured 1/4 cup of the oil using the spouted measuring cup and poured that slowly down the side of the spice jar until it formed a layer on top of the water and the jar was 3/5 full.

5. Finally, after wiping out the inside of the measuring cup, we poured 1/4 cup of green rubbing alcohol into the spouted measuring cup. Then we poured the alcohol slowly along the side of the spice jar until the jar was 4/5 full. (If the rubbing alcohol is clear, then before adding it to the spice jar you can add a drop or two of (another) food coloring and stir the solution until the color is uniform throughout.)

The result is a 'layered lava lamp’ that beautifully demonstrates the different *densities* of the liquids (and the air in the 1/5 layer above them).

Because I had one more empty spice jar, we taped an illuminated light and button battery to its bottom and created a Bubbling Lava Lamp using the following ingredients in order:

* 1 Tbs baking soda - place in bottle first

* Vegetable/Olive Oil - fill bottle 4/5 full

* White Vinegar mixed with food coloring - add dropwise to the jar.

Then we put the lid on the jar and watched the glowing bubbles that formed in our concoction.

When it stopped fizzing, we mixed 1-2 Tablespoons of baking soda with water and added that drop-wise, watching it fizz even more. In fact, we had to wait for the fizz to die down before we could put the cap back on the bottle. The bubbles continued for more than 30 minutes.

When we tired of watching our DIY lava lamps, we watched the following videos and discussed their contents:

and

Then we did some density experiments of our own, seeing what objects floated in which layer of an ‘experimental’ lava lamp (nobody wanted to mess theirs up).

It turned out to be quite an easy, inexpensive, engaging, and *effective* lesson. I hope you'll try it at home :-)

If you have enjoyed one or more of my posts, please support my writing, social media management, and educational workshops by visiting www.MelissaRooneyWriting.com and ordering one of my STEM-based picture books for a child in your (or a friend's) life. Thanks in advance!! ~ Melissa