Get Wet! Water Science at the Library

I’ve been continuing to do monthly science programs for grades 4-6 at the Burlingame Library.  It’s a challenge finding activities that are interesting enough for that age group, but easy and inexpensive enough to coordinate with a class of 25 kids.  I’m always a little bit nervous to see how the projects will work, but I am loving the interactions with the kids, who are always enthusiastic and full of ideas.  This month’s topic was Water.  I had three projects planned: a paper clip challenge, to introduce surface tension; a clay boat challenge, to introduce buoyancy; and an electrolysis project, to demonstrate the composition of water.

I started out with a conversation about what the kids already knew about water: that it’s made up of two hydrogen atoms and one oxygen; that it makes up most of our bodies and the earth’s surface; and all of the different ways we use it, from growing food to generating energy.

Then I had the kids go to the tables, and gave them each a paper clip and a paper bowl half full of water.  I told them that their challenge was to get the paper clip to float on the surface.  The tools they could use were a tissue or another paper clip.  Some of the kids were able to get the paper clip to float by very carefully setting it on the surface of the water with their fingertips.  Others lowered the paper clip onto the water with a tissue, which would sink, leaving the paper clip floating.  A few kids actually took pieces of cardboard from the tissue box and made little rafts for the paper clip.  None of them used the second paper clip idea (you can partially straighten the second paper clip and use it to lower the first one onto the surface), but they all found a solution.  I gave a brief explanation about how this was another demonstration of surface tension: the water molecules clinging together create a kind of a “skin” on the top of the water.


Paper clip floating on the water due to surface tension


Their second challenge was to get a ball of Sculpey clay to float on the water.  This was by far the thing that excited them the most.  It took them a minute or two to come up with the idea of shaping the clay into boats.  After that they were all eagerly making Sculpey boats and asking if they could add different components, like paper clip sails.  They could have happily spent the whole rest of the class doing that.  We discussed the idea of buoyancy, the upward force that the water exerts on objects.  I demonstrated buoyancy by pushing a ping pong ball to the bottom of a cup of water, and showing how it shot up to the surface when I let it go.  I didn’t get to go into the details of Archimedes’ principle, so I’d like to come back to that in a future class.


Boat made out of Sculpey clay to demonstrate buoyancy

The last part of the class was the electrolysis activity.  First, I had to show them the acid/base indicator we were going to use: the juice of a red cabbage (I used a juicer, but you can also just boil the leaves).   I demonstrated that when you add vinegar (an acid) to the red cabbage juice, it turns pink, and when you add baking soda (a base) to the juice, it turns green.  I explained that we were going to use electricity to split water into hydrogen gas (H+) and hydroxide (OH-).

I gave each student a 9 volt battery, two short pencils that had been sharpened at both ends, and some poster tack.  They still had their bowls of water from the previous activities, and I added a small amount of red cabbage juice to each bowl (we found the experiment worked better if the water was only slightly bluish).  I also added a spoonful of Epson salt to each bowl, and explained that it make the electrolysis work more effectively.

The biggest challenge the kids found was getting the pencils to adhere to the battery terminals with the poster tack without breaking the pencil tip or preventing the tip from touching the metal of the battery.  In some cases, I had the kids remove the poster tack altogether, and just hold the pencils in place while they lowered the other ends into the bowls of water.  Once they did that, the water would bubble around the pencil tips.  Hydrogen ions (H+) collect at the positive terminal of the battery, making the water more acidic, and turning the cabbage juice pink.  Hydroxide (OH-) ions collect at the negative terminal, forming a base, and turning the cabbage juice green.


Electrolysis of water with a red cabbage juice pH indicator.  The pink color indicates the formation of Hydrogen (H+) ions, while the greenish color indicates Hydroxide (OH-).

It was a fun class overall, although I think it has inspired to do more construction based challenges in the future, since they had so much fun making the boats.  I would love any ideas for future classes, so please share them in the comments.



Circuit Training: Basic Electronics at the Library

This week’s Sizzling Science theme for fifth and sixth graders at the Burlingame Library was Fun with Electronics.  For this one, I stole an idea from the Maker Faire in San Mateo, as well as a project recommended by my coworker, Carbelle Imperial.  The first was a popsicle stick flashlight, and the second a Brush Bot.  This was by far the most expensive workshop I’ve done so far, since I bought the Brush Bot kits from the Maker Shed (a pack of 12 costs $34.99, and I needed 2 packs).

I started out by talking to the kids about electronics, asking them where the word comes from, and discussing what electrons are (one of the three parts of an atom, and the one that carries a negative charge).  I brought out a AA battery, and pointed out the positive and negative terminals.  I explained that a chemical reaction inside the battery causes electrons to build up at the negative end.  The electrons want to travel to the positive end, but cannot travel through the battery itself because of a substance inside called a separator.  (I passed around this diagram from Online Digital Education Connection to illustrate the different parts of the battery.)  I pulled out a piece of aluminum foil and used it to connect the two battery terminals, then walked around to let the kids feel how hot the foil had become, using it as an illustration of a very basic circuit.

It was clear that three or four of the kids already had a great deal of background knowledge of electronics, and were quick to answer questions.  Most of the group stayed quiet though, so it was hard to gauge how much they knew.

I told the kids that they would be using a simple circuit to make a flashlight, and asked them what parts they thought they would need (some of them had already sneaked a peek at my model when they came in the door, so they knew a lot of the answers).  The parts were: a 5mm white LED, a 3-volt lithium coin battery, 1/2″ copper foil tape (which I had pre-cut), jumbo-sized popsicle sticks, small binder clips, and Scotch tape.  We talked a little bit about the function of each part, and I pointed out that the LED had a long leg (the positive lead), and a short one (the negative lead).

In retrospect, I should have handed out each part a step at a time.  As it was, I handed out all the materials at once, and a number of the kids jumped right in without waiting for instructions.  That left me with a lot of troubleshooting to do, and several of them had to start over.  On the other hand, making mistakes and then correcting them may have taught them more than blindly following the steps, so I guess it worked out.

Anyway, the basic process is this:

1) Run a strip of copper foil down one side of the popsicle stick.  Make a small roll of foil at the end, leaving sticky spot close to the center of the stick.

2) Attach the battery to the sticky roll of foil.  The positive (+) side of the battery should be down, touching the foil.  (This was one of the most common mistakes).

3) Clip the binder clip on the end of the popsicle stick closest to the battery.  Flip the metal leg of the clip down.  It should rest on top of the battery.  If it doesn’t reach, adjust the foil and battery to move the battery closer.

4) Flip the popsicle stick over, and run the second strip of copper foil down that side.  Again, when you flip the metal leg of the binder clip down, it should rest on the foil.

5) Place the LED on the end of the popsicle stick opposite the binder clip, with the long leg (positive lead) straddling the side with the battery.  Both legs should be touching the foil tape on each side of the popsicle stick.  If both legs of the binder clip are down, the LED should light up.  If it’s working, tape the legs of the LED down with the Scotch tape.

6) Now you have a simple flashlight with a switch.  To turn it off, flip the top leg of the binder clip back away from the battery.

A completed popsicle stick flashlight

A completed popsicle stick flashlight

The bottom side of the popsicle flashlight

The bottom side of the popsicle flashlight

Some common problems the kids ran into were: putting the LED on backwards (with the short leg on the battery-side of the popsicle stick instead of the long one); running the copper tape over the end of the popsicle stick (in those cases, I just tore the foil, so it was no longer connected); putting the battery on upside down (with the positive side facing up; and putting the battery too close or too far away from the binder clip (sometimes the kids had the hold the binder clip down against the battery to keep the light from flickering). Incidentally, you could make the flashlight with the positive side of the battery facing up, as long as the LED was also attached the opposite way, with the long leg facing the battery-side of the popsicle stick.

I did this project with the kids all sitting in a circle on the floor, to make it easier to distribute supplies and handle questions.  The funny thing was that this project was intended to be a more defined, step-by-step activity, but by now the kids were so used to coming up with their own ideas and prototypes, that many of them went off to tinker with the design, and add extra LEDs (one boy had five!).

A flashlight with 5 LED's

A flashlight with 5 LED’s

Once everyone had a working flashlight, I asked them to move to the tables, and brought out the Brush Bot project.  This one was much more straightforward.  It’s basically a tiny robot made from the head of a toothbrush, a vibrating micro pager motor (the thing that makes cell phones vibrate) with adhesive on one side, and a coin battery.  The coin battery is encased in a plastic cover with two wires coming out.  I had cut the heads off the toothbrushes ahead of time, cut the adhesive tape included with the kit into small pieces, and trimmed the wires, stripping the plastic back to leave a 1/4″ of copper.

All the kids had to do was stick the motor on top of the battery, use a piece of adhesive to stick the battery onto the toothbrush, and twist the ends of each of the wires from the motor around the ends of one of the battery wires (it doesn’t matter which one).  If it works, the motor vibrates, and the brush twirls around (the battery and motor will also move around without the toothbrush, so it might be fun to experiment with that or with other types of bases).  The kit comes with stickers for the kids to decorate their robots.

A brushbot decorated with pipe cleaners

A brushbot decorated with pipe cleaners.  The small black circle on the top is the vibrating motor.  The yellow disc beneath it is the battery.  It is attached to the toothbrush with an adhesive strip.

I had to do a fair amount of troubleshooting with this project too.  The biggest, and most frustrating, problem was that some of the batteries didn’t seem to work. (I checked them over later, and found that they had lost some of their voltage.  They could still light an LED, but were no longer strong enough for the motor.  I did find a simple workaround though: I had a few coin batteries left over from the flashlight project, so I helped the kids use Scotch tape to attach one of the motor wires to the positive terminal of one of those batteries, and the other wire to the negative terminal.  It worked just as well, and helped reinforce the idea of creating a circuit. In fact, I think if I could find a cheap source for the micro pager motors, it might be an easier and less expensive way to do this project.

A Brush Bot with the motor attached directly to the positive and negative terminals of a 3V button battery

A Brush Bot with the motor attached directly to the positive and negative terminals of a 3V coin battery

I gave the kids some pipe cleaners to add appendages to their robots.  By this time, they were off creating all kinds of new designs.  My favorite was a kid who attached a toothbrush head to his popsicle stick flashlight, and made a vibrating toothbrush with an on/off switch!


A vibrating toothbrush with on/off switch

I’m still amazed by the kids in these workshops.  They have so much creativity and enthusiasm, and I’m almost sad to see this workshop series come to an end.  Next week’s theme is Hot and Cold, so we are making ice cream in a bag and homemade thermometers.  I’m just hoping it’s not too messy!  Wish me luck!

Crazy Chemistry: More Summer Science in the Library

Although I was nervous last week about my first summer science workshop for 5th and 6th graders at the Burlingame Public Library, I was surprised at how excited I was to do this one.  I had set the theme as “Crazy Chemistry,” but had trouble finding projects that were not too time-consuming or involved equipment that would difficult to use in the library.  I finally settled on making a naked egg, an acid-base experiment, and a homemade lava lamp.  It ended up being a lot of fun, and thankfully did not end in a giant mess on the carpet.

Here’s what we did:


A Naked Egg

A Naked Egg

I learned about this from my coworker, Carbelle Imperial, who had demonstrated it in her Make It classes at the Pacifica-Sharp Park Library. I added extensions from Steve Spangler Science (Here’s his description:

This was really more of a show-and-tell than a hands-on project, but it made a great lead-in to the topic of chemistry.  I had soaked three eggs in vinegar in my refrigerator three days before.  After the first 24 hours, I put one of the eggs in water that I had dyed green, another in corn syrup, and a third in fresh vinegar.  Basically, the vinegar, (acetic acid) reacts with the calcium carbonate in the eggshell and slowly dissolves it, leaving only a soft translucent membrane to hold the egg white and yolk.  The egg in fresh vinegar also absorbed extra fluid, making it much larger than normal.  The egg in the green water was also supposed to swell to a larger size, but mostly it just turned green (I think I should have left it in the vinegar for at least another day before putting it in the water).  The egg in corn syrup shrank, and became slightly saggy, since some of the water molecules had passed from the egg into the syrup.

Naked Egg Soaked in Corn Syrup

Naked Egg Soaked in Corn Syrup

To start this week’s workshop, I had the kids sit in a circle on the floor.  We talked briefly about chemistry, and how it is the study of matter.  I said that I always think of mad scientists mixing chemicals, but that chemistry can be used to identify and learn more about substances, as well as to make new things.  Then I pulled out a fresh egg and a bottle of vinegar.  I put the egg in a plastic container, which I filled with vinegar.  After a few seconds, tiny bubbles began to form all over the surface of the egg.  I explained that vinegar is a mild acid that dissolves the shell around the egg.  Then I passed around each of my naked eggs, one at a time, and explained each one.


The Naked Egg discussion made a great intro to the next project.  Since we had been working with vinegar, a mild acid, I said we were now going to find out how to determine if something was an acid or a base.  I asked the kids if they knew of an example of a base, giving them the hint that it was something that reacts with vinegar.  One of the kids guessed baking soda, so I pulled some out and gave a very brief demo of baking soda mixed with vinegar in a plastic container.

Before the class, I had put a head of red cabbage in my juicer and diluted the juice with water in a large jar.  I passed this around for the kids to smell (P-U!), and also showed them another head of cabbage so they would know what it looked like.  I explained that red cabbage leaves contain a substance called anthocyanin, which changes color when it is exposed to an acid or a base.  I poured a small amount of my cabbage juice into two Dixie cups, and then put a tiny amount of vinegar in one, and baking soda in the other.  The vinegar turned the cabbage juice bright pink, while the baking soda turned it a blue-green color.

Left: Red Cabbage Water mixed with Baking Soda (a base); Center: Red Cabbage Water alone; Right: Red Cabbage Water mixed with vinegar (an acid)

Left: Red Cabbage Water mixed with baking soda (a base); Center: Red Cabbage Water alone; Right: Red Cabbage Water mixed with vinegar (an acid)

I then pulled four plastic bottles containing different “mystery” substances, labelled A, B, C, and D, and told the kids that they were going to test each one to determine whether it was an acid or a base.  (A was lemonade, B was baking soda mixed with water, C was vinegar, and D was water).  I divided the kids into pairs, and gave each of them four Dixie cups.  I poured a small amount (about an eighth of the cup) of the cabbage juice into each of their cups, and gave them paper and pencils to take notes on their results.  I passed around the different mystery bottles, with a straw to use as a dropper for each one (I showed them how to dip the straw into the liquid, and put a finger over the end to carry a small amount of the liquid over to the testing cups).

The kids seemed to have fun doing the experiment.  Many of them guessed that A was lemonade (the yellow color was a giveaway).  They were confused about the water, which of course didn’t have any effect on the cabbage juice, but a number of them figured that out too.  I was impressed by the notes that they took.  Several of them made simple charts to track the results, while one team made a number of observations about the look and smell of each liquid.

At the end, I asked the kids which of the substances they might want to drink, and asked if anyone would like some Mystery Liquid A.  I had a couple of bottles of lemonade set aside, and we took a short break to drink some.  I explained that lemonade contained citric acid, and joked that they could tell people they had been drinking acid at the library (ha ha).


Lava Lamp with Alka Seltzer added

Lava Lamp with Alka Seltzer added

This project appears on a lot of web sites, including Steve Spangler Science:  It’s very simple, but it was a big hit with the kids.  I started out by showing them one I had pre-made, a water bottle filled with vegetable oil and water that I dyed green with food coloring.  I asked the group why the water and oil were separated.  Most of them knew that oil and water didn’t mix, and I elaborated by explaining that the water is denser than the oil and sinks to the bottom, because the molecules are so tightly packed together.  (I read recently that there are more molecules in a glass of water than there are known stars in the universe).  I went on to talk about how the water combines with the food coloring, but the oil does not.  I realized later that I could have gone into more detail about how water molecules are polar, with positive and negative poles like a battery, while the oil is nonpolar, with a shell of negative charges surrounding each molecule, and that polar and nonpolar molecules don’t mix well.

Since I was nervous about the carpet in the room I was working in, I added the oil to the bottles myself, filling each one about three-quarters full.  The kids then carried the bottles to the sink to fill them up the rest of the way with water.  I had them work at one big table for the rest of the project.  They each chose the color they wanted to dye the water, and dropped several drops of food coloring in.

Now for the big moment: I pulled out an Alka Selzer tablet and broke it up, dropping the pieces into my lava lamp.  The Alka-Selzer reacted with the water to create bubbles of carbon dioxide, which carried the green water droplets to the top of the bottle, where they would pop, and the water would sink back down.  The kids loved that part, and were eager to get their own Alka-Selzer tablets.  They spent the rest of the class happily plopping and fizzing.  I stretched a balloon over the top of my bottle, and showed them how it would fill up partially with air from the carbon dioxide.  They were eager to try that too.  Thankfully there were no brightly-colored oil spills!

The Carbon Dioxide in the Alka Seltzer will partially fill a balloon stretched over the mouth of the bottle

The carbon dioxide in the Alka Seltzer will partially fill a balloon stretched over the mouth of the bottle

At the end of class, I let them rinse the outside of their bottles off in the sink (they had all gotten a bit oily), and sent them home with their lava lamps and extra Alka Seltzer.  All-in-all, I had a great time, and they seemed to too.

Next week’s theme is Physics, and I’m planning to make Marshmallow Catapults.  I’m expecting a sugary battlefield.  Wish me luck!