Density Experiments

I am beginning a week entirely devoted to hands-on experiments involving Chemistry, Physics, and Biology.

To start the week, we explored density by making a liquid rainbow using salt, water and food coloring. 

Getting the ratio of salt to water right IS KEY!!!

I looked up a couple directions online and did a test run at home first. The first picture is what I was able to accomplish with the following proportions:

• ALL: ~9 oz water
• Blue water: 4 TEASPOONS salt
• Green: 3 teaspoons
• Yellow: 2 teaspoons
• Red: 1 teaspoon

( you could modify the salt so that there is barely any or none in the last one... since freshwater floats about salt water)

Using a pipette, collect the most dense color first (blue). The more salt added, the heavier the solution gets, thus more dense than regular water.

VERY slowly squeeze water out into your cup or beaker. As you add the other colored layers on top it is important to :

a) squeeze slowly and carefully

b) do so very close the water's surface and along the side of the cup AND angling the pipette helps as well.

We had 4 oz beaker cups, so my instructions for the kids were a ounce of each color (fill blue up to 1, green up to 2, yellow 3.. etc)

Getting the salt ratio right is sometimes trial and error. The first round I didn't have my note sheet with me and messed up the amount of salt I put in... and it made a very visible difference. 1-2 kids who were very patient and careful were able to get about 2 different visible layers. After I reconfirmed the amount of salt to water, we all did a second trial of the experiment and it worked much better! Kids with lots of patience and focus had a better pipetting technique, resulting in a overall better rainbow. 

This was a great tie-in to discuss the Hudson River and that it is a tidal estuary, meaning it has a mix of salt and freshwater.

This project should be done in a VERY well lit area or close to a window. Even though we were in a big room with several windows... most of the time as the kids were layering their entire cups of water looked very dark against the brown wood tables. Holding right up to the window made the appearance better. My practice run over the weekend was conducted right next to a bright window. Below is what a majority of kid's projects looked like. Even though you can't see on these pictures too well,, we did have some visible blue on the bottom and when held up to the sunlight, some orange/yellow.

Sink or Float?

During snack time I showed everyone two containers. One with a egg sinking in freshwater and one with the egg floating in saltwater. I asked the kids if they could guess why. (obviously because the salt makes the water heavier) And my kids who were participating in the experiment earlier were quick to shout out and not give others time to think... but nonetheless it was a good, quick little demo to give other kids not usually participating in env. programming a taste of what we had been learning today.