Density Rainbow: Difference between revisions

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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]], [[Chemistry]]:
| Density, Buoyancy
|-
| Grade Range:
| [[Elementary School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School
Elementary students love this demonstration, and are often very interested in watching the liquids sort. This demonstration has two methods to present it; one with a variety of solutions, and the other using only sugar solutions.


== Format ==
== Materials ==


Hands-on
===Method A===
* Graduated Cylinder (500mL)
* Various Liquids, such as:
** Liquid Soap
** Water
** Corn Syrup
** Lamp Oil
** Vegetable Oil
** Glue
* Small objects to put in (Paper clips, bits of wood, plastic, etc.)


== Materials ==
===Method B===
* 1 Large Beaker (600 mL)
* 5 Small Beakers (140-150 mL)
* Sugar
* Water
* Spoon
* Food Dye (Red, Yellow, Blue, Green)


    Sugar
===Method C===
    Three small cups to mix solutions in
* 1 Large Beaker (600 mL)
    One large (~8oz), clear cup that will be easy to see into (thinner is better)
* 3 Small Beakers (140-150 mL)
    Three types of food coloring
* Hot Plate
    A tablespoon measuring spoon
* Ice
    A plastic spoon
* Water
    A funnel
* Food Dye (Red, Green, Blue)
    A supply of clean water if you will be presenting multiple times
* Spoon
    A water basin to clean materials between performances
    A towel to dry off the measuring spoon


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Demonstrators should wear goggles and lab coats, and the ST general safety box should be available to them. While the materials involved in this demonstration are not particularly dangerous, care should always be exercised to ensure the safety of the audience and to avoid messes. The sugar solutions should not be consumed!
Please read the Liquid Chemical section of the [[Demonstration Safety]] page before performing this demonstration.
 
== Preparation ==


Make sure a large basin of clean water is available. You should use this water to clean the materials between performances. If the cleaning water becomes too saturated with food coloring, replace it. Make sure clean water is available for making the solutions.


== Demonstration ==
== Demonstration ==


In the three small cups, add one, two, and three tablespoons of sugar, respectively. Make sure the measuring spoon is dry before you insert it in the sugar! Be sure to remember which glasses have the most and least sugar. You could write out signs to place next to the glasses to help the audience remember which one is most dense. Add three tablespoons of water to each cup. Stir the sugar-water solutions very well (for about 30s each) to dissolve as much sugar as possible. Add about two drops of different food coloring to each cup. Because yellow food coloring tends not to be very strong, it should be added to the least-dense solution, if used at all, so that it's not overwhelmed by seepage from a higher layer.
===Method A===
 
# Set the graduated cylinder on a table with a bin or tablecloth underneath to catch any spills. Add 100 mL of water to the cylinder before the start of the event.
Add the highest density solution to the large, clear cup. Now place the plastic spoon upside down in the clear cup so that the bottom of the spoon just touches the top of the solution. Slowly and carefully pour the medium-density solution over the back of the spoon on top of the high-density layer. This is necessary because it is important to avoid letting solutions plunge into previous layers, as the food colorings will mix and the rainbow layering will not be preserved. Repeat the process carefully with the low-density layer. If done correctly, the clear gas will have well-defined (though not sharp) layers of different density solutions of different colors.
# Let students add one of the other liquids in (but only a small amount) and watch where it ends up. Is it above or below the water? As more liquids are added, they will sort themselves by density, and students will be able to see some clear distinctions between the liquids!
# Let students know that the density of something is equal to its mass divided by the volume it takes up. Give them a small object and ask them to predict where it will float in the cylinder before dropping it in. Was their prediction correct?


== What to Say ==
===Method B===
# Measure out 100 mL of water into each of the small beakers. Add three drops of food coloring to four of the beakers, with each getting only one of the colors.
# Add sugar to each of the colored beakers. Give two teaspoons to red, five to yellow, eight to green, and eleven to blue. Mix each one thoroughly, rinsing or wiping the spoon between beakers so that a beaker doesn't get too much or too little sugar.
# In the big beaker, first add the blue solution. Then, to add the rest of the solutions in color order, ending with clear, by pouring them slowly over the back of the spoon to prevent splashing and mixing. If done correctly, the solutions will stack on each other, creating a rainbow!


As you're preparing the sugar solutions, let the audience see that the sugar dissolves into the water. You may want to discuss saturation: ask the audience what would happen if you introduced a large amount of sugar into a small amount of water.
===Method C===
# Measure out 100 mL of water in each of the beakers. Start heating one on the hot plate, and add ice to another and let it cool down.
# Add 2 drops of food dye to each of the beakers; red in the hot beaker, green in the room temperature beaker, and blue in the cold beaker.
# Once the hot beaker is hot, turn off the heat plate. Add the blue water to the large beaker first. Then add the green water, pouring it over the back of a spoon to ensure it spreads out and doesn't mix much. Repeat for the red water, and if done correctly the solutions should stay mostly separated!
# The solutions will mix over time as the temperatures become more balanced, so plan to reset this demonstration every 15 minutes or so.


Optionally, you could discuss solubility. You could give examples of substances that do not dissolve in water.


When you're finished stirring in the sugar, show the audience the three cups. They saw that you used three times as much sugar in the first cup as the last, but the volume of the two solutions are similar. Use this to illustrate your discussion of density. Make sure to note that density is defined as mass divided by volume.
== Why This Works ==


Ask the audience if they know which is more dense: pure water or salt water. Ask them if they've ever heard of the Dead Sea between Israel and Jordan, which has about 35% salt concentration, as opposed to about %3 for typical seas [3]. Explain that people can float in the Dead Sea effortlessly because the density of the water is higher than the density of the human body. You might want to use the examples of life preservers or rafts to illustrate that objects float if they are less dense then the surrounding liquid.
''Density'' is equal to the mass of a substance divided by the volume it takes up. Water has a density of 1kg/L, and can be used as a base for finding how dense other liquids are. Liquid soap and corn syrup are both more dense than water, so you will see them fall underneath it, while oils are less dense than water, so the lamp oil and vegetable oil would float on top. solid objects have differing densities as well. When the paper clips or other small objects are dropped in, they will sink below some layers and float on top of others! How well an object floats is what we call ''buoyancy''. If we know the buoyancy of an object, then we can calculate the mass of the object.


Before you layer the solutions, ask the audience if they think any of your three solutions could float on top of the others. Make sure they can guess the ordering correctly. Ask them why you need to add the solutions so slowly and carefully.
The sugar water variation of this demo is a great way to show that liquids that look the same can have different densities. The sugar water does not take up much more volume, or space, than the regular water. However, the sugar water has more mass per volume than the regular water, which means that it has a higher density. The more sugar there is dissolved in solution, the more mass there is per volume, and therefore the density will get higher.


Finally, ask the audience if they think it would be easier to swim in very salty water than in a regular swimming pool. You could introduce the concept of viscosity to explain that, even if it is easier to float in saltwater, it would be more difficult to propel yourself. You could ask the audience to think about swimming in honey or mud. Make sure the audience understands that typical saltwater doesn't have high enough salinity for this effect to be significant for human swimmers, but that it might be important for microscopic organisms in seawater [2].
The temperature version of this demo shows the students how a substance can change in density if the temperature changes. If something is hot, then the atoms and molecules have more energy, and can take up ''more'' space, or volume, while having the same amount of mass, and there be less dense. Likewise, if a substance is cooled down, then it will take up ''less'' space, or volume, with the same amount of mass, and be more dense! By simply heating up or cooling down a solution, we can affect the density of it!


== Why it is ==
== Additional Information ==


== Real Life Examples ==
* This pairs well with the [[Cartesian Diver]] demonstration.

Latest revision as of 20:30, 6 May 2016

Physics, Chemistry: Density, Buoyancy
Grade Range: Elementary School
Format: Hands-on

Elementary students love this demonstration, and are often very interested in watching the liquids sort. This demonstration has two methods to present it; one with a variety of solutions, and the other using only sugar solutions.

Materials

Method A

  • Graduated Cylinder (500mL)
  • Various Liquids, such as:
    • Liquid Soap
    • Water
    • Corn Syrup
    • Lamp Oil
    • Vegetable Oil
    • Glue
  • Small objects to put in (Paper clips, bits of wood, plastic, etc.)

Method B

  • 1 Large Beaker (600 mL)
  • 5 Small Beakers (140-150 mL)
  • Sugar
  • Water
  • Spoon
  • Food Dye (Red, Yellow, Blue, Green)

Method C

  • 1 Large Beaker (600 mL)
  • 3 Small Beakers (140-150 mL)
  • Hot Plate
  • Ice
  • Water
  • Food Dye (Red, Green, Blue)
  • Spoon

Safety Precautions

Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.


Demonstration

Method A

  1. Set the graduated cylinder on a table with a bin or tablecloth underneath to catch any spills. Add 100 mL of water to the cylinder before the start of the event.
  2. Let students add one of the other liquids in (but only a small amount) and watch where it ends up. Is it above or below the water? As more liquids are added, they will sort themselves by density, and students will be able to see some clear distinctions between the liquids!
  3. Let students know that the density of something is equal to its mass divided by the volume it takes up. Give them a small object and ask them to predict where it will float in the cylinder before dropping it in. Was their prediction correct?

Method B

  1. Measure out 100 mL of water into each of the small beakers. Add three drops of food coloring to four of the beakers, with each getting only one of the colors.
  2. Add sugar to each of the colored beakers. Give two teaspoons to red, five to yellow, eight to green, and eleven to blue. Mix each one thoroughly, rinsing or wiping the spoon between beakers so that a beaker doesn't get too much or too little sugar.
  3. In the big beaker, first add the blue solution. Then, to add the rest of the solutions in color order, ending with clear, by pouring them slowly over the back of the spoon to prevent splashing and mixing. If done correctly, the solutions will stack on each other, creating a rainbow!

Method C

  1. Measure out 100 mL of water in each of the beakers. Start heating one on the hot plate, and add ice to another and let it cool down.
  2. Add 2 drops of food dye to each of the beakers; red in the hot beaker, green in the room temperature beaker, and blue in the cold beaker.
  3. Once the hot beaker is hot, turn off the heat plate. Add the blue water to the large beaker first. Then add the green water, pouring it over the back of a spoon to ensure it spreads out and doesn't mix much. Repeat for the red water, and if done correctly the solutions should stay mostly separated!
  4. The solutions will mix over time as the temperatures become more balanced, so plan to reset this demonstration every 15 minutes or so.


Why This Works

Density is equal to the mass of a substance divided by the volume it takes up. Water has a density of 1kg/L, and can be used as a base for finding how dense other liquids are. Liquid soap and corn syrup are both more dense than water, so you will see them fall underneath it, while oils are less dense than water, so the lamp oil and vegetable oil would float on top. solid objects have differing densities as well. When the paper clips or other small objects are dropped in, they will sink below some layers and float on top of others! How well an object floats is what we call buoyancy. If we know the buoyancy of an object, then we can calculate the mass of the object.

The sugar water variation of this demo is a great way to show that liquids that look the same can have different densities. The sugar water does not take up much more volume, or space, than the regular water. However, the sugar water has more mass per volume than the regular water, which means that it has a higher density. The more sugar there is dissolved in solution, the more mass there is per volume, and therefore the density will get higher.

The temperature version of this demo shows the students how a substance can change in density if the temperature changes. If something is hot, then the atoms and molecules have more energy, and can take up more space, or volume, while having the same amount of mass, and there be less dense. Likewise, if a substance is cooled down, then it will take up less space, or volume, with the same amount of mass, and be more dense! By simply heating up or cooling down a solution, we can affect the density of it!

Additional Information

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