This super easy salt water experiment is the perfect kitchen science experiment to teach kids about the density of salt versus fresh water. With summer approaching and beach trips planned it’s a great time to learn about how salty ocean water is different from fresh river water. At the end of this post you will find 20 more ocean-themed learning activities to do with the kids!
A Little Bit of Background
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I was so excited to learn about the ocean with my kids! There are so many fascinating animals and undiscovered areas of the ocean.
Before doing our science experiment we took some time to watch the two episodes about ocean life on Planet Earth. (If you haven’t seen these AMAZING wildlife documentaries you are missing out! Check out these DVDs from the library or get them from Amazon ASAP!)
Once we had some solid background knowledge about the ocean we set up our salt water experiment. This was the first time I introduced the kids to a “controlled variable”. (The thing you don’t change so you can compare other things to it.) My little scientists are growing up.
Salt Water Experiment
We headed to the kitchen to gather the following items:
- Small plastic jewels (We purchased ours at the dollar store. If you don’t have these exact jewels, don’t worry. You can use raw eggs or small grapes instead. I did a similar Halloween-themed salt water experiment that you can see here.)
- Several clear cups full of water
- Baking Soda
*Feel free to test other substances like washing soda, baking powder, sand, cornstarch, etc. It’s always fun to experiment to see what happens!
Once we had our supplies gathered we followed these instructions to do our salt water experiment:
- Dissolve 2 tablespoons of salt in one cup, 2 tablespoons of sugar in another cup, and 2 tablespoons of baking soda in a third cup. Be sure to leave one cup as plain, fresh water. (This is the controlled variable.)
- Label each cup so everything stays organized.
- Have the kids think about what might happen when they drop the jewels into each cup. Will the jewels sink or float?
- Drop the jewels into each cup to find if the kids’ guesses were correct!
*Hint: You may need to add more salt/sugar/baking soda to the water, depending on what kind of jewels or food you are using in this experiment. Add enough that you can see some extra powder on the bottom of the cup. The salt water and baking soda water should make the jewels float. Read below to find out why!
The Science of the Salt Water Experiment
When you add salt to water it makes the water more dense. This means it gets heavier. Many objects that sink in fresh water will float in salt water!
Objects float in baking soda water because baking soda is a kind of salt. It dissolves in water to make the water more dense, just like table salt does. However, baking soda has another property that gave us a little bit of a surprise!
When baking soda dissolves in water some of it reacts to form carbon dioxide gas. If you look carefully you will see tiny bubbles rising from the bottom of the cup. We must have added just the right amount of baking soda to the water because when we put the jewels in the cup they hovered right in the middle! Over time the tiny carbon dioxide bubbles attached to the plastic jewels and acted like tiny life preservers, carrying the jewels to the top of the cup. It was absolutely FASCINATING to watch that process! My son loved watching the jewels slowly rise to the surface.
Give this fun and easy science experiment a try while you learn about the ocean this year! And be sure to check out the list below for more ocean-themed activities from some of the most creative bloggers on the web.