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      Density, Buoyancy and Ketchup!

      Sometimes science can look a lot like magic. This lab experiment is no exception! Floating and sinking ketchup, here’s how you make it happen!

      What You’ll Need:
      – 1 Liter plastic bottle, or clear water bottle
      – Fast food ketchup packet
      – Salt (preferably kosher salt)
      – Water

      Step One:

      Remove any labels from the bottle and fill it completely with water.

      Step Two:

      Add your ketchup packet, and see if it floats or sinks.

      Step Three:

      If your ketchup packet sinks, add 3 tablespoons of kosher salt to the water. Cap the bottle, give it a shake, then repeat by adding more salt until the ketchup packet floats in the bottle.

      Step Four:

      When your ketchup packet is floating – either naturally or after adding the salt – make sure the bottle is completely full of water and close the cap tight.

      Step Five:

      Squeeze the bottle from both sides. The ketchup packet should sink as you squeeze and float as you release the
      pressure on the bottle.

      How Does It Work:

      This lab experiment is a practice in buoyancy and density. It was buoyancy that determines if the ketchup packet floats. When it does not, adding salt to the water made it more dense than the ketchup packet, allowing it to float.

      There is a small air bubble in the ketchup packet, so once it is comfortably floating in the water, squeezing the bottle puts
      pressure on that bubble and decreases its size. That decreases the packet buoyancy and increases its density – therefore, the packet sinks when you squeeze.

      This demonstration is sometimes referred to as a Cartesian Diver. To make it a true experiment, try this again with mustard, soy sauce or other condiment packets.

      These experiments are intended for inquiring young chemists and their adult supervisors. In all experiments, responsible adults should assist throughout to ensure proper safety precautions are followed. Eye goggles, gloves, etc. may be required.

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