Osmosis - Naked Eggs (Lisa Hellinger)

Author:

Lisa Hellinger

Principle(s) Illustrated:

• Osmosis, the diffusion of water from an area of higher water concentration to an area of lower water concentration is demonstrated using a shell-less chicken egg. With the shell removed students have the opportunity to see the effects of different solutions on a cell with a selectively permeable membrane. Eggs will be placed in water, a sugar solution and a salt solution. The concepts of hypertonic and hypotonic will be discussed.

Standards:

NGSS Science & Engineering Standards

• Developing and Using Models

  • Modeling in 9–12 builds on K–8 experiences and progresses to using, synthesizing, and developing models to predict and show how relationships among variables between systems and their components in the natural and designed worlds.

  • Develop a model based on evidence to illustrate the relationships between systems or components of a system. (HS-LS2-5)

• Constructing Explanations and Designing Solutions

  • Constructing explanations and designing solutions in 9– 12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.

  • Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. (HS-LS2-3)

NGSS Cross-cutting Concept Standards

• Structure and Function

  • Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem. (HS-LS1-1)

• Systems and System Models

  • Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions including energy, matter, and information flow - within and between systems at different scales. (HS-LS1-2), (HS-LS1-4)

• Stability and Change

  • Much of science deals with constructing explanations of how things change and how they remain stable. (HS-LS2-6),(HS- LS2-7)

NGSS Disciplinary Core Idea Standards

• Structure and Function

  • Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1)

Questioning Script:

Prior knowledge & experience:

• Solutes tend to move from an area of high concentration to an area of low concentration

• Membranes are selectively permeable

Root question:

• What happens to a shell-less egg that is placed in water, a salt solution, or a sugar solution?

• What is the process that can explain what is observed?

Target response:

• Eggs placed in water will get larger or gain mass because the concentration of water outside the cell is greater than inside the cell and the water from the jar moved into the egg.

• Eggs placed in a salt solution will get smaller or lose mass because the concentration of water outside the cell is less than inside the cell and the water from the egg moved into the jar.

• Eggs placed in a sugar solution will get smaller, lose mass because the concentration of water outside the cell is less than inside the cell and the water from the egg moved into the jar.

Common Misconceptions:

• All cells are microscopic

• Diffusion and osmosis do not occur across nonliving membranes

• Egg shells or cell walls are substitutes for cell membranes

• Water doesn't move along a concentration gradient only solutes do

Materials & Procedures:

Materials:

• 4 Raw eggs with shells removed

• 250 ml of vinegar in sealed mason jar

• 250 ml of water in sealed mason jar

• 250 ml of corn syrup in sealed mason jar

• 250 ml of salt water in sealed mason jar

• Plastic spoons

• Paper towels

• Balance

Procedures:

• Remove Shells (Start 2 days before activity)

  • Replace with fresh vinegar every 24 hours until shell is completely dissolved

• Allow students to handle eggs and write down observations

• Note initial mass of each shell-less egg

• Assign a team of students to each jar

• Place one egg in each mason jar

• Teams time lapse video to document event

• Teams write down observations

• Note final mass of each egg

• Discuss students' explanations

Other Variations:

• What is happening when the egg is placed in vinegar?

  • The reaction is: CaCO₃+ 2H⁺ -> Ca⁺² + H₂O +CO₂

  • The shell composed of calcium carbonate is dissolved.

  • The bubbles observed are the release of carbon dioxide gas. (Students will think it is oxygen.)

Photographs and Movies:

Egg shell dissolving in vinegar.

Shell-less egg in water Shell-less egg in corn syrup

(hypotonic solution) (hypertonic solution)

Left egg after gaining water from soaking in water.

Right egg after losing water from soaking in corn syrup.

References:

Even More Brain-powered Science (NSTA)

Everything You Know About Osmosis is (Probably) Wrong