“The Bends”: Henry’s Law & Deep-Sea Gas Solubility - Student Investigation

Part 1: Engage (Anchoring Phenomenon)

Phenomenon: Scuba divers who ascend too quickly from deep dives can suffer from a painful and potentially fatal condition known as “the bends” (decompression sickness). Similarly, if you open a warm bottle of soda, it fizzes and goes flat much faster than a cold bottle.

Reflect:

1. Why do you think gas bubbles form in a diver’s bloodstream during a rapid ascent?
2. What “need to know” questions do you have about how temperature and pressure affect gases dissolved in liquids?

Part 2: Explore (Simulation Investigation)

Use the “The Bends”: Henry’s Law & Deep-Sea Gas Solubility simulation to investigate these variables.

Instructions:

1. Initial Observations: Start the simulation at the default target depth (300 meters) and a temperature of 20°C. Observe the “Gas Tissue Content” graph and note how quickly gas enters the tissues.
2. Pressure Investigation:
   • Use the slider to change the target depth to a shallower depth (e.g., 50 meters) and then a deeper depth (e.g., 500 meters).
   • Observation: How does the depth (pressure) affect the final equilibrium amount of dissolved gas?
3. Temperature Investigation:
   • Set the depth to 150 meters. Use the temperature slider to compare the gas content at 5°C versus 35°C.
   • Observation: How does changing the temperature affect the amount of gas dissolved in the tissues at equilibrium?

Part 3: Explain (Sensemaking)

Using your data, answer the following questions:

1. Collision Theory and Temperature: Based on collision theory, temperature is a measure of average kinetic energy. When the temperature increases, what happens to the kinetic energy and frequency of collisions of the dissolved gas molecules? How does this explain why less gas stays dissolved at higher temperatures?
2. Pressure and Concentration: According to Henry’s Law, the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid. As pressure (depth) increases, what happens to the concentration of gas molecules available to collide with the liquid surface? How does this increase the rate of gas dissolving into the tissues?

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

Scientific Argument: Construct a scientific explanation that answers the question: How do changes in temperature and pressure affect the rate and amount of gas that can dissolve in a liquid?

Your argument must include:

• A clear Claim answering the prompt.
• Evidence gathered from your simulation investigations (specific effects of depth and temperature).
• Reasoning that connects your evidence to collision theory, kinetic energy, and Henry’s Law, specifically mentioning how the number and energy of molecular collisions affect the rate of dissolution.