Hidden bubbles

We found this effect quite by accident. One of Jr. scientist A's new favorite things to do is to mix various ingredients together to see what happens - I think we have a budding chemist! We were adding things to red cabbage-dyed water (a pH indicator). As expected, when we added baking soda, the mixture turned blue, and adding vinegar to the same mixture caused it to bubble and then turn red. What caught us by surprise was that we next added salt and the mixture bubbled again. I had never heard of salt causing a chemical reaction resulting in bubbles, so we did some more investigating. Adding more salt turned the mixture from red (acidic) to purple, as would happen when you added a base, making us think that salt was a base (it's actually neutral). We tried combining vinegar and salt in another cup and got a rather unexciting cup of salty vinegar with no bubbles. After some google-ing, we found out that the salt wasn't actually creating bubbles, it was releasing the carbon dioxide bubbles trapped in our mixture after the baking soda and vinegar reaction. We decided to try adding salt to soda and got instant bubbles again. We even were able to create a little soda fountain (nowhere near as big as the mentos and diet coke reaction, but still cool). Jr scientists A and E both got quite a kick out of this accidental experiment, and I think it will become a new regular experiment.

Stalagmites and stalactites, take 3

Never willing to admit defeat, we've made another try at making stalagmites and stalactites. We noticed that the area around our crystal experiments was covered with crystals. It seems that the salt water evaporated in the hot sun, but was too heavy to stay in the air and condensed out. We decided to take advantage of this to try to grow stalactites. We put a mesh (a cut-out from a screen door) on top of the jar for our latest experiment, hoping it would catch the escaping evaporated salt water. We poured our crystal making materials into the jar while it was covered by the screen so some of the liquid would stay on the screen and start a layer of crystals for the rest to hang on to. We weren't able to grow stalactites with this technique, but we got an unexpected but happy result. The evaporated salt water seemed to get trapped inside the jar so we ended up with one big thick crystal that covered the bottom of the jar. Pretty cool. I want to try this in a disposable cup next time so we can easily get the crystal out to play with. It looks like we'll finally have crystals that aren't to delicate to handle.

Ice melting experiment

We had previously used salt to briefly drop the melting point of ice. This time we tried it on a larger scale. We made two ice cubes. The first one (red in the video) was made using water that had Epsom salt dissolved in it. The second one (green in the video) was made using plain water. This wasn't exactly the cleanest experiment - the plain water cube ended up noticeably bigger and was frozen for a shorter period since we already had salt ice cubes sitting around - part of a long-term experiment I'll write about when it's finished. But I expected the effect to be large enough that the general results would be unaffected. As shown in the video, the salt ice cube did melt much faster (about half an hour compared to 1.5 hours for the albeit larger plain water ice cube). You can see from the pool around the edge of the plate how much quicker the salt ice cube was melting. The two ice cubes also melted in very different ways. The plain water cube primarily just got smaller. It still had the typical smooth edges of an ice cube. The salt ice cube started looking very rough and "eaten away" even though it started out smooth. The one oddity was that the plain water ice cube started melting much quicker. We may need to do a more controlled experiment. Although Jr. scientist A enjoyed watching the ice cubes melt, I was surprised that he showed little interest in the sped up video, which I thought would be easier for him to grasp.

Stopping color in its tracks

This experiment was hard to pull off, but very cool once we got it to work. Since salt water is denser than fresh water, you should be able to get fresh water to sit on top of salt water, rather than all mixing together. The idea is that you put clear salt water in one container and fresh water with food coloring in another container. When you poor the colored water into the container with the salt water, the colored water should sit on top of the salt water, giving the appearance that you've stopped the color in its tracks. The only problem is that the force of pouring the colored water makes it go to the bottom of the second container before rising to the top, coloring the salt water in the process. Remembering how we got a paper clip to float using surface tension, we floated a piece of cardboard on top of the salt water and carefully poured the colored water onto the cardboard. The trick worked - although we had one attempt where some of the colored water missed the cardboard, greatly diminishing the wow factor. But when it worked, it was surreal.

Turning salt into glue

We tried to pick up ice cubes with string, using salt as the "glue." The idea is that, when you put salt on ice with the string resting on the ice, the salt lowers the ice's melting point, causing it to start to melt a little. As it refreezes, the ice freezes around the string. Our first attempt was a dud. You could feel that the string stick a little to the ice, but pulled right off. But it turned into an accidental experiment on states of matter - jr. scientist A was delighted to find that when he held the ice in his hand, it turned into water. For our second attempt, we realized that we needed to first wet the string. That turned out to be the key. With our salt and wet string, we were able to lift up the ice - although the effect was somewhat short-lived.

Water race

To try to show that, even though water looks the same after you dissolve salt in it, it's changed, we decided to compare the speed of diffusion for salt water and fresh water. We filled one bottle with fresh water, dyed green, and a second bottle with water with Epsom salt dissolved into it, dyed red. Then we rolled up a paper towel and put an end in each bottle. The green fresh water started climbing the paper towel. At first it looked like the red salt water was just sitting there, but we checked and the un-dyed paper towel coming from the red was wet, while the paper towel from the fresh water was only wet where it was green. Eventually the red color started moving along the towel. It looks like the salt slowed the diffusion of the color, but not the diffusion of all the water.