Students investigate how the surface area of a solid affects the rate of a chemical reaction by comparing how long it takes whole, broken, and powdered Alka-Seltzer tablets to dissolve in water.

1. Gather materials: three Alka-Seltzer tablets, timer, paper, heavy object (for crushing), beaker or cup, and tap water.
2. Fill a beaker or cup with a fixed amount of water (e.g., 250 mL).
3. Drop in one whole Alka-Seltzer tablet and measure the time it takes to fully dissolve. Record the result.
4. Break the second tablet into several smaller pieces, add to a fresh beaker of water, and time the reaction. Record the result.
5. Crush the third tablet into a fine powder, add to another beaker of water, and measure the dissolution time.
6. Compare the times and calculate the average reaction rate for each condition.

Alka Seltzer Reaction - Pueblo Science:

📄 Reaction Rates: When Surface Area Matters! - Science Buddies: https://www.sciencebuddies.org/teacher-resources/lesson-plans/surface-area-reaction-rates

• Test the effect of water temperature on dissolution speed.
• Use different brands or types of effervescent tablets for comparison.
• Compare the effect of stirring versus no stirring.

• Safety glasses recommended to protect against splashes.
• Handle the crushing of tablets carefully to avoid injury.
• Clean up spills immediately.
• Dispose of the used solutions down the sink with running water.

• Which form of the tablet dissolved the fastest, and why?
• How does collision theory explain the differences in reaction rates?
• What real-world examples can you think of where surface area affects reaction speed?
• How might increasing temperature or concentration influence reaction rate compared to surface area?