Introduction
Astound students as a blue liquid in a wave bottle “switches” from the bottom layer to the top.
Concepts
- Density
- Immiscibility
- Polar/nonpolar molecules
- Hydrogen bonding
Materials Included In Kit
Blue food dye solution, 400 mL
Lamp oil, 400 mL
Lamp oil, blue, 400 mL
Bottle, square, plastic, PETG, 1000-mL, 2
Additional Materials Required
Water, distilled or deionized water, 400 mL
Materials
Blue food dye solution, 400 mL*
Lamp oil, 400 mL*
Lamp oil, blue, 400 mL*
Water, distilled or deionized water, 400 mL
Bottle, square, plastic, PETG, 1000-mL, 2*
*Materials included in kit.
Safety Precautions
Lamp oil (kerosene) is a flammable liquid; moderately toxic by ingestion, inhalation and skin absorption. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron when preparing the density bottles. Do not allow students to open the prepared bottles. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Disposal
Bottles may be reused for years.
Prelab Preparation
- Rinse each of the 1000-mL plastic bottles with water to remove any dust or other particles that may be present.
- Empty the contents of the bottle containing clear lamp oil into one of the 1000-mL plastic bottles.
- Pour the entire bottle of blue food dye solution into the same 1000-mL plastic bottle as the clear lamp oil.
- Tightly cap the bottle.
- Pour all of the blue lamp oil into the empty 1000-mL plastic bottle.
- Add 400 mL of distilled or deionzied water to the same bottle with the blue lamp oil. The layers in this bottle should be the reverse of the first bottle. Note: Do not use tap water—it tends to be cloudier in appearance than distilled or deionized water.
- Tightly cap the bottle. The bottles will not need to be reopened once they are prepared.
Procedure
- Present students with one of the bottles.
- Encourage students to handle the bottle. Have them gently shake the bottle, turn it upside down, on its side, etc., observing the layers as they move and separate. Note: Vigorous shaking may result in numerous trapped air bubbles that may give the layers a cloudy appearance for a while.
- Discuss the concepts of density, immiscibility and polar/nonpolar properties with students.
- Leave the bottle at a visible location in the classroom, such as a front table, for a few days.
- Remove the bottle when students are not present and replace it with the other bottle.
- Students will notice that the layers are reversed. This will initiate questions and discussion on density and other related topics.
- At this point it may be beneficial to present both bottles to students simultaneously.
Teacher Tips
- When students first notice that the layers have “switched,” do not immediately tell them they are looking at a different bottle. Ask for explanations of how this “switch” may have occurred.
- Ask students whether they believe the bottles contain the same two liquids and the reasoning behind their answers. Do the layers in both bottles behave in a similar fashion?
- Caps may be glued onto the bottles to prevent opening, spillage or tampering.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Asking questions and defining problems
Developing and using models
Constructing explanations and designing solutions
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
HS-ESS2.C: The Roles of Water in Earth’s Surface Processes
Crosscutting Concepts
Structure and function
Performance Expectations
MS-PS2-2: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object
MS-ETS1-1: Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
MS-ETS1-2: Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.
MS-ETS1-3: Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.
MS-ETS1-4: Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.
HS-PS2-1: Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
HS-PS3-3: Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.
HS-ETS1-2: Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.
Answers to Questions
- Draw the two bottles. Label each with chemicals and colors in the correct place.
{12568_Answers_Figure_1}
- Water has a density of 1.0 g/mL. Approximate what the density of lamp oil might be. Give a reason for your guess.
The density of lamp oil may be around 0.8 g/mL. It has to have a density lower than that of water, 1.0 g/mL, because the water layer sits below the lamp oil layer in both bottles.
- The water and lamp oil layers do not mix because lamp oil is a hydrocarbon, which is nonpolar. Water, on the other hand, is a polar molecule. What does this say about the blue dye used in this demonstration? Why do you think that only the water was blue in one bottle, but only the lamp oil was blue in the other?
The blue dyes used in the demonstration have to be different for each substance. Only a polar substance would bond readily with water, so the dye in water must be polar. The dye in lamp oil, on the other hand, must be a nonpolar substance so that it bonds with the lamp oil but not with the water.
Discussion
{12568_Discussion_Figure_1_Water molecule with partial charges}
The bottles both contain water and lamp oil. Lamp oils are petroleum byproducts primarily composed of liquid paraffin. The density of lamp oil is between 0.8 g/mL and 0.9 g/mL, which is less than that of water which has a density of 1.0 g/mL. The difference in densities results in the more dense water layer on the bottom.
The two liquids in each bottle are immiscible, that is they will not intermix to form a solution. Lamp oil is composed of hydrocarbons which have a general chemical formula of CNH(N × 2)+2. The difference in electronegativity values between carbon and hydrogen is small. When they form molecules, electrons are almost equally shared within the carbon and hydrogen bond. As a result, the carbon hydrogen bond has little change separation or polarity. Hydrocarbon molecules are nonpolar and hydrophobic (water repelling) in nature, since water, H2O, is a polar molecule. Oxygen and hydrogen have very different electronegativity values causing an uneven distribution of electrical charge resulting in partial charges, a dipole. The geometry of water keeps the partial charges separated and causes water molecules to be polar (see Figure 1).
{12568_Discussion_Figure_2_Hydrogen bonding between water molecules}
As shown in Figure 1, the electronegative oxygen atoms in water molecules have a partial negative charge. Hydrogen atoms from other water molecules will be drawn to this negativity due to their partial positive charge, resulting in an attractive force called hydrogen bonding. Water molecules have greater attraction to one another due to hydrogen bonding than they do to other nonpolar molecules such as hydrocarbons (see Figure 2). The strong attraction between water molecules causes them to be tightly packed in the liquid state. This means there will be more water molecules (mass) per unit volume of liquid compared to nonpolar liquids.
The blue color in the water comes from food coloring, which is a polar substance, so it mixes readily with water. When the bottle is shaken the oil will not become tinted from contact with the food coloring due to the incompatibility of polarity. The blue coloring in the lamp oil comes from an oil-miscible dye which is nonpolar. Water will not become colored due to the difference in properties between the water and the dye present in the oil.
References
Special thanks to Lee Marek, University of Illinois at Chicago; Naperville North High School, Naperville, IL (retired) for providing the idea and the instructions for this activity to Flinn Scientific.
|
