At Home With Hands On!

Hot n’ Cold Water Tower (2/1/17)

 

Photo Credit: John K. and Morgan B.

Photo Credit: John K. and Morgan B.

 

MATERIALS:

  • Four transparent, heat-resistant Glasses (they must have the same sized lip, or opening)
  • Water
  • Liquid Food Dye
  • Water Pitcher
  • Card Stock (Note Cards, Gift Cards, even Playing Cards will work as long as they can completely cover the Glass)
  • Microwave, Teakettle, or other water-heating device
  • Ice Cubes
  • Lots of Paper Towels!
  • Ice Cube Tray
  • A Grown-up Assistant

INSTRUCTIONS:

  1. Lay down several Paper Towels over a flat, clean surface. There will likely be a lot of water spilled in this experiment, and the Paper Towels will help catch all of the mess!
  2. Fill a Water Pitcher with cold water. Add several Ice Cubes to the cold water to get it really chilly. Set it aside.
  3. Ask a Grown-up Assistant to heat more water until it is hot, but not boiling, in a Teakettle or microwave-safe container. Because some water will spill in this experiment, and you do not want to pour boiling water all over the place, don’t overheat the water! Set it aside.
  4. Choose two Food Dye colors to represent Hot water and Cold water. You can choose any two colors that you’d like; but remember that the colors MIGHT mix together, and some color mixtures aren’t very pretty. Try using the primary colors (Yellow, Red, or Blue) or get creative!
  5. Add a few drops of your Hot water Food Dye color to two of your heat-resistant glasses. To the other glasses, add a few drops of your Cold water Food Dye color.
  6. Completely fill up the glasses with the corresponding temperature of water (fill the glasses with your Cold water Food Dye color with ice water, and the glasses with Hot water Food Dye with the hot water.)
  7. Experiment 1: Cover the opening of one Cold water glass with your Card Stock. While firmly holding the Card Stock against the lip of the glass, lift the glass, flip it over, and carefully place it squarely onto one of the glasses full of Hot water.
  8. While your Grown-up Assistant holds the top and bottom glasses in place, carefully slide out the cardstock from between the glasses. Observe what happens to the colored waters in each glass. Do the colors mix together? If so, why? If not, why not?
  9. Experiment 2: Cover the opening of the remaining Hot water glass with a dry piece of Card Stock. While firmly holding the Card Stock against the lip of the glass, lift the glass, flip it over, and carefully place it squarely onto the remaining glass of Cold water.
  10. While your Grown-up Assistant holds the top and bottom glasses in place, carefully slide out the cardstock from between the glasses. Watch what happens to the colored water in each glass this time. Do the colors mix together? If so, why? If not, why not? What was different about the experiment this time? What does this tell us about Hot and Cold water?

HOW DOES IT WORK:

Dihydrogen monoxide, or Water, is a chemical substance composed of two Hydrogen atoms and one Oxygen atom per molecule. At normal temperatures, these molecules exist in the liquid state. If you raise the temperature of the water (make it hotter), the water molecules will move around more quickly and they will begin to spread further apart from each other and take up more room. On the other hand, if you lower the temperature of the water (make it colder), the water molecules will slow down, and they will begin to group more tightly together.

This change in heat (and the subsequent change in molecular movement) of the water will change another important quality of the water: its density. Density is a measurement based on two characteristics: how much stuff (or mass) fits into a certain space (volume). That is, substances with a lot of stuff (in this case water molecules) squeezed into a small space has very high density. Substances with less stuff (water molecules) spread out over more volume have very low density.

Hot water has a lower density than Cold water, because the water molecules have spread out into a larger volume!

Okay then, why do the colors mix together in the first experiment? When you place the Cold water on top of the Hot water, the two water samples quickly switch places, or flip. The less-dense Hot water rises up into to the top glass, and the Cold water sinks down to the bottom glass. In this sudden change of places, the two colors of Food Dye will mix together inside of the glass.

solubility 1

And why do the colors NOT mix together in the second experiment? When you place the Hot water on top of the Cold water, the Hot water remains floating above the Cold water because of its lower density! Since the two water samples don’t mix together, neither do the Food Dyes.

solubility 2

THE MORE YOU KNOW:

Lakes and large ponds have different layers of water that can act much like the water layers in our experiments. Typically, the highest layer of water (known as the Epilimnion) floats on the top, like in Experiment 2, because the warmer water is less dense than the water in the deepest and coolest layer (known as the Hypolimnion). However, if the surface water temperature rapidly cools down through the change of Seasons, the top layer of water can suddenly become colder than the lowest layer of water, and the waters will actually flip, like in Experiment 1.

 

GOING ONE STEP FURTHER:

  1. So far we have only experimented with liquid water at different temperatures. But what would happen if we used solid water (also known as ice) in the experiment? Freeze a tray of ice cubes that have been colored with your Cold water Food Dye color. Add a colored Ice Cube to each of your glasses of Cold water before repeating the Experiments. Observe what happens to the ice cubes. Did you expect these REALLY Cold ice cubes to float or sink, knowing that Cold water sinks?
  2. Are there ways to float water on top of water that is the same temperature? Fill two glasses with water that is the same temperature. Color each glass with a different color of Food Dye. To one glass, add a few tablespoons of Sugar and stir until completely dissolved. Repeat the Experiments with your glasses of Water and Sugar Solution. Which one do you think will float?
  3. Iced Tea also demonstrates this idea of water turning. Don’t believe me? Throw a few ice cubes into a glass of warm tea. The ice will quickly rise to the surface because ice crystals are actually less dense than liquid water. But as the ice begins to melt, take a REALLY close look at the tea just around the ice cubes. Do you see those swirls of clear water moving out from the ice? That’s melted ice—water that is cooler and more dense than the warm tea around it. As we have already seen, this chilly water immediately sinks! Now that’s some Sweet Science!