Try this at home: Make your own “bubbling cauldron”

SAC I

Want to bring a little science into the home?

For young (and young-at-heart) scientists, here is a simple science experiment developed by McGill science students as part of the WOW Lab project.

Whether it’s at Hogwarts or a Halloween party, there’s something fascinating about a bubbling potion. Here’s how to make a simple water and oil mixture bubble like a witches’ brew without having to bother toads, bats and other hard-to-find ingredients.

oil and water

What you need:

• pitcher of water

• pourable container of vegetable oil

• 500 mL beaker or large glass jar

• salt

• sugar

• measuring cup

• tablespoon

 

What to do: 

  1. Fill the jar or beaker three-quarters full with water.
  2. Pour oil into the jar or beaker, so that a layer of oil at least 1 cm thick forms above the water level, You can use a tablespoon to dispense the exact volume of oil.
  3. Add salt until oil droplets begin to sink to the bottom of the beaker. Some of the oil droplets at the bottom of the beaker will begin to float back to the surface.
  4. Adding additional salt once the droplets rise will cause the droplets to descend. The sinking and rising of the oil droplets can be repeated until the water becomes saturated with salt

Question!

But will it work with sugar? Let’s find out…

  1. Empty the beaker
  1. Fill the jar or beaker three-quarters full with water.
  1. Pour oil into the jar or beaker, so that a layer of oil at least 1 cm thick forms above the water level, You can use a tablespoon to dispense the exact volume of oil.
  1. Add sugar until oil droplets to sink to the bottom of the beaker. Unlike the salt/oil droplets, the sugar/oil droplets do not ascend, but instead stay at the bottom of the beaker.

Why it works (or doesn’t!)

When salt or sugar is added, the density of the oil droplets is increased, making the droplets more dense than water and causing them to sink. Eventually the salt leaves the oil to dissolve in the water, reducing the density of the oil and causing the droplets float back up to the surface. The sugar droplets will not float back up, because the sugar does not leave the oil.

About WOW Lab

The McGill WOW Lab is Research and Development project that ran from TK to 2013. Student researchers created over 40 “blueprints” for hands-on science activities, specially designed to enhance the K-12 Canadian science curriculum. For more projects – and more detailed instructions for this one – check out the WOW Lab website.   Link to WOW Lab Web site: http://wowlab-blueprints.mcgill.ca/en/projectpage.php?id=cauldron Link to video, to be embedded: https://www.youtube.com/watch?v=6f4KCBYVLYM

 

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