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STEM activity of the week – Fun for all ages!

(Week 3) Eggshell Geode Crystals

https://sciencebob.com/eggshell-geode-crystals/

This project nicely demonstrates how real-life geodes are formed in igneous and sedimentary rock. It also demonstrates super-saturated solutions and shows a nice variety of crystal shapes and formations.

YOU WILL NEED:

  • clean eggshells
  • water
  • a variety of soluble solids: table salt, rock salt, sugar, baking soda, Epsom salts, sea salt, borax, or cream of tartar
  • small heat proof containers (coffee cups work well)
  • spoons
  • food coloring
  • egg cartons and wax paper or mini-muffin tins

WHAT TO DO:

  1. Crack the eggs for this project as close to the narrow end as possible. This preserves more egg to use as a container for the solution.
  2. Clean the eggshells using hot water. The hot water cooks the lining and allows you to pull the skin (egg membrane) out of the inside of the egg using your fingers. Make sure to remove all the egg membrane, if any membrane stays inside the shell it is possible that your eggshell will grow mold and your crystals will turn black.
  3. Use an egg carton lined with waxed paper or mini-muffin tins to hold the eggs upright.
  4. Use a saucepan to heat the water to boiling. .
  5. Pour half a cup to a cup of water into your heatproof container. If you poured half a cup of water into the container, add about a ¼ cup of solid to the water. Stir it until it dissolves. Likewise if you used a cup of water, add about ½ a cup of solid to the water. You wanted to add about half again the volume of the water as a solid to the mixture. When the initial amount of solid is dissolved continue adding small amounts of the solid until the water is super-saturated. Super-saturated simply means the water has absorbed all it is able to absorb and any solid you add will not dissolve.
  6. Add food coloring.
  7. Carefully pour your solution into the eggshell, filling it as full as possible without over-flowing it or causing it to tip.
  8. Find a safe place to put your shells while the water evaporates. Crystals will form inside the eggshells as the water evaporates.

HOW DOES IT WORK?

Dissolving the crystals in hot water created what is called a “super-saturated solution.” This basically means that the salts took advantage of the energy of the hot water to help them dissolve until there was no more space between molecules in the solution. As the solution cooled, the water lost its energy and the crystals are forced from the solution to become a solid again. Since this happens slowly along with the evaporation, the crystals have time to grow larger than they were when the experiment started. Natural geodes in rock are form in much the same way as mineralized water seeps into air pockets in rock. This is also how rock candy crystals are formed.


(Week 2) Homemade Ice Cream

https://sciencebob.com/easy-to-make-ice-cream-in-a-plastic-bag/

You will need:

  • 4 oz of milk
  • 4 oz of cream
  • 1/4 tsp of vanilla (or use other flavors usually found near the vanilla in a grocery store – you can use chocolate syrup for chocolate ice cream)
  • 4 tsp of sugar
  • A few drops of food coloring (optional – if you want colorful ice cream)
  • Lots of ice
  • Lots (half cup) of salt. Rock salt (sold at hardware stores) works best.
  • Small (quart size) zip-lock freezer bag
  • Large (gallon size) zip-lock freezer bag

What to do:

  1. Put the milk, cream, flavoring, coloring, and sugar into the SMALL zip-bag and zip it shut (be sure it is zipped up and closed completely)
  2. Put about a cup of ice into the large bag and the cover the ice with a small handful of salt. Put the small bag with your ingredients into the larger bag.
  3. Add some more ice and then some more salt. Keep adding salt and ice until the bag is almost full.
  4. Zip it shut (be sure it is zipped) and then carefully hold opposite sides of the bag and shake the bag back and forth (like your steering a car) for about 5-8 minutes.
  5. Open the larger bag and take out the smaller bag – it should be full of ice cream! Rinse off the bag under running water to remove any salt that may be near the opening of the bag.
  6. Open and enjoy!

The Science of Ice Cream

When you added salt to the ice, the chemistry between the two forced the ice to melt. Before the ice could melt though, it needed to borrow heat from objects that surround it. This is called an ENDOTHERMIC process. Since your ingredients are not as cold as the ice, it borrowed heat from your ingredients making them colder! When they get colder, they freeze up into ice cream. Yum!


(Week 1) The Egg Drop Challenge

https://sciencebob.com/try-the-egg-drop-challenge/

You will need:

  • 1 plastic cup of water with a mouth wide enough to fit the egg.
  • 1 10” (25 cm) piece of cardboard or a small tray with a SMOOTH bottom
  • 1 cardboard tube (paper towel or toilet paper tubes work well)
  • 1 Egg (uncooked for more drama)

What to do:

  1. Place the tray centered over the cup
  2. Place the tube on its end in the center of the tray
  3. Place the egg horizontally on the tube
  4. When ready, strike the tray hard enough with your palm to send the tray flying, but not so hard you hit the glass of water. If all goes well, the tray and paper tube will go flying, but the egg will safely drop into the water.

How does it work?

INERTIA describes an object in terms of how much energy is needed to move it or stop it from moving. Since the tray and tube are very low mass (lightweight,) they have very little inertia, and will easily move out of the way.
The egg, however, is heavier (has more inertia) and so it is not easily moved, leaving it in place for gravity to bring it down into the cup.