THIS DAY IN SCIENCE: Post and Gatty attempt to circumnavigate world in 1931

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Float When It’s Denser

This activity helps to illustrate the particle theory and how it applies to solutions.  Some earlier work using the particle theory is a prerequisite. Dissolving salt into water increases the water’s density, allowing more dense materials to float in the salt water which would have sunk in unsalted water.

What to Do

  1. Fill a clear glass with cold water. Gently place a raw egg into the glass and observe the position of the egg.
  2. Fill a second clear glass with cold water and gently place a raw egg into the glass. Observe the position of the egg. Measure spoons full of salt and add them to the water until the egg rises to the surface.  Note the amount of salt required to raise the egg.
  3. Repeat step 2 using hot water. Note the amount of salt that is needed to raise the egg.
  4. Repeat step two using a hardboiled egg. Note the amount of salt required to raise the egg.
  5. Note the position of the hardboiled egg. Crack open the egg and note the location of the yolk.
  6. Mark one cm intervals on the straws with the waterproof permanent marker. Add a lump of modeling clay to the bottom of the straws. Place the straws in the glasses. Note the height of the straw in the glasses, which determines the density of the liquids.
  7. Pour milk, juice, or other liquids into clear glasses and use the hydrometer to compare their densities.


066 Gr 7 Matter – Float When It’s Denser

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