Science Buddies: "Ask an Expert"

Hi
My daughter is testing whether water can float on water, with temperature and salinity as key variables.

She knows colder water is denser and warmer water floats. She knows higher salinity is denser, so lower salinity water does float on higher. BUT proving it with colored water has been a challenge. Its hard to see the warmer red non-salty water rise to the surface. It all just turns purple. Any ideas to actually PROVE - with data - what we know? how measure???

thank you!

Hi! I actually think that the water turning purple makes sense! You just need to try the inverse experiment to see the red water floating on the blue water. Here's what I mean...

There are two experiments in this project-
1) the red (less dense) water is on the bottom and the blue (more dense) water is on top, then the separator is removed.
2) the blue (more dense) water is on the bottom, red is on top, and then the separator is removed.

In the first experiment, the red water will move up because it is less dense and mix with the blue water, turning purple, like you observed. This actually makes sense- Because both liquids are water, once they're mixed the dyes will not spontaneously unmix, so you'll never see separation of the red onto the top.

It sounds like you haven't tried the second experiment. This one is much more convincing!

By the way, I found a video of someone doing this experiment on YouTube and it looks like it worked really well with their setup, so if you're having any technical difficulties it might be helpful to watch this!

Good luck and let me know if you have any questions!
Megan