Science Demonstrations

It’s time for some science demonstrations with Purdue University College of Agriculture. Allie Kingery, in Purdue Food Science, demonstrates how to make Molecular Gastronomy Cheese. While students in the Department of Biochemistry walk us through how to make slime and lava lamps.

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Ingredients:

12 oz cheese (no limits to the variety: we used fontina, bleu, and gouda)

2/3 cup of water

1 tablespoon of sodium citrate (found online as food ingredient)

Directions:

  1. Shred cheese and set aside.
  2. Combine sodium citrate and water in small pot and whisk until sodium citrate is mostly dissolved.
  3. Simmer mixture—no need to boil.  Add one small handful of cheese and stir continuously as cheese melts.  Keep adding cheese, handful by handful.  Once all cheese is melted, mixture should be smooth and flowable.  If not, add water a tablespoon at a time while stirring until sauce is created.
  4. To use as a sauce: pour immediately onto food item (tortilla chips for nachos) or keep warm to use as a dip (fondue).
  5. To use as cheese slices: pour onto a wax-paper lined tray. Allow to chill in refrigerator (up to 1 week) and slice when ready.  Slices can be re-melted on top of a burger patty or as part of a grilled cheese sandwich.

So why use sodium citrate?

Many cheeses are not great at melting smoothly, and result in an oily, clumpy mess. If you have tried to heat an aged cheddar, you would likely have had this experience!  Sodium citrate is used to contribute to the protein solubility in the cheese while targeting a pH favorable for melting. It is found in many food products and can aid in including your favorite cheese into your next mac and cheese, grilled cheese sandwich, nachos, or more!

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Materials

2 - 50mL falcon tubes

1 popsicle stick

10 ml Elmer’s glue

Food coloring

10 ml saturated borax solution

10 ml water

Preparatory Steps

  1. Prepare saturated borax solution
  2. Mix borax into water at 0.01 g/mL (10 g/L) and microwave for 3 minutes
  3. Too little borax makes the slime sticky while too much borax makes the slime brittle
  4. Fill a 50mL falcon tube with 10mL of Elmer’s glue
  5. Fill a second 50mL falcon tube with 10mL of Elmer’s glue
  6. Add 10mL of water to the tube with glue in it

Procedure

  1. Add 2-3 drops of food coloring to the tube with borax solution
  2. Ensure caps are on tightly before shaking both tubes
  3. Pour the colored tube with borax into the tube with glue and water
  4. Cap the tube
  5. Mix contents by shaking capped tube vigorously or use a popsicle stick to stir
  6. Remove slime from tube and play

Discovery Questions

  1. What do you think is in the tubes?
  2. Water, glue, and borax
  3. What is borax?
  4. A detergent used to clean
  5. Are these solids or liquids?
  6. Liquids
  7. If we mix these two liquids together, will we get a solid or liquid?
  8. Solid
  9. What do you think happened?
  10. Borax linked the glue polymers together

Explanation

Glue is made of a molecule that looks like a bunch of long chains. Borax connects all of those chains making it stronger. The stronger molecules make a gooey solid instead of a liquid.

Advanced Explanation

Glue contains an ingredient called polyvinyl acetate that forms long chains making it a polymer. The term “polymer” comes from words that mean “many parts”. Those polymers aren’t connected to each other until the borax is added. Borax acts as a “cross-linker” which connects each of those chains to each other making a more solid slime compared to the liquid properties of glue. It does this using hydrogen bonding. Hydrogen bonds are fairly week, so they can be broken and reformed while playing with the slime.

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Materials

1 – 50mL Falcon tube

10mL water

20mL vegetable oil

Food coloring

Alka Seltzer (1/4 of a tablet)

Preparatory Steps

  1. Fill the 50mL Falcon tube with 10mL of water
  2. Add 20mL of vegetable oil to the tube

Procedure

  1. Add 2-3 drops of food coloring to the tube
  2. Add ¼ of a tablet of Alka Seltzer to the tube
  3. Watch. Do not cap the tube until the bubbling has stopped

Explanation

Clearly water and oil do not mix. This is because water is polar and oil is not. It has to do with how the molecules are made. Water is shaped like a “V” and the electrons aren’t shared equally between the two hydrogen atoms and one oxygen atom. This means one end is slightly negative and the other end is slightly positive. Oil isn’t like this and shares its electrons evenly between its carbon and hydrogen atoms. Polar molecules like water hang out with other polar molecules and nonpolar molecules like oil hang out with other nonpolar molecules.

Alka Seltzer reacts with the water at the bottom to make tiny bubbles or carbon dioxide. The bubbles grab onto the colored water as they float to the surface. At the top, the bubbles pop and the colored water will sink back down to the bottom.

Discovery Questions

  1. Why don’t the water and oil mix together?
  2. Water is polar and vegetable oil is nonpolar.
  3. Why does water sink to the bottom and oil stays on top?
  4. Water is denser than oil.
  5. Do you think food coloring is polar or nonpolar?
  6. Polar because it mixes with the water and not the oil.

New to transplanting a seedling to a larger pot?  Watch this quick guide to getting started.

Find more resources through the Purdue Extension Online Resources for Gardeners page

or watch this video series for First Time Gardeners