Experiment 12.2: Chemical Weathering Model

Student Information

Purpose

To model chemical weathering and observe how different substances affect limestone (chalk).

Background Information

Chemical weathering occurs when chemicals in water react with minerals in rock, causing the rock to break down or dissolve. This is one of the primary ways that Earth's surface changes over time.

Limestone is a sedimentary rock primarily composed of calcium carbonate (CaCO₃). In nature, limestone is particularly susceptible to chemical weathering when exposed to acidic solutions. When acid comes into contact with limestone, it reacts with the calcium carbonate, causing it to dissolve.

The chemical reaction between an acid and limestone can be represented as:

CaCO₃ + 2H⁺ → Ca²⁺ + H₂O + CO₂

In this experiment, we will use chalk (which is made of calcium carbonate, the main component of limestone) to observe chemical weathering. We'll compare the effects of water (a neutral substance) and vinegar (a weak acid) on the chalk to simulate how acidic rain and other natural acids weather limestone in nature.

Materials

Safety

IMPORTANT: Always wear eye protection during this experiment.

Vinegar is a mild acid but can cause eye irritation. If vinegar gets in your eyes, rinse immediately with plenty of water.

This experiment should be conducted in a well-ventilated area.

Wash your hands after handling the materials.

Procedure

  1. Place one piece of chalk on each plate or bowl.
  2. Take a dropper full of water and begin by placing a drop on one piece of chalk.
  3. Observe what happens when the water reacts with the chalk or limestone.
  4. Continue placing drops of water on the chalk until you have added 5-10 drops. Record your observations.
  5. Now repeat the procedure but use drops of vinegar on the second piece of chalk.
  6. Record your observations after dropping each drop until you've added 5-10 drops of vinegar.
  7. When you have finished dropping the water and vinegar on each chalk piece, pick up what's left of the chalk.
  8. Do you notice anything left on the plate? This is sediment resulting from chemical weathering.
  9. Compare the amount of sediment left on each plate and record your observations.

Data Collection

Observation Point Water + Chalk Vinegar + Chalk
Initial reaction (first drop)
After 5 drops
After 10 drops
Sediment left on plate
Changes to chalk appearance

Analysis Questions

1. Which liquid caused more noticeable changes to the chalk? Why do you think this happened?

2. How does this experiment demonstrate chemical weathering? Explain the chemical reaction that occurred.

3. In nature, what substances might act like vinegar to weather limestone? Give examples.

4. How is the weathering observed in this experiment different from mechanical weathering?

5. What natural landforms or features might result from chemical weathering of limestone? Research and explain.

Conclusion

Summarize what you learned about chemical weathering from this experiment. Explain how this relates to real-world geological processes and landform development.

Extension Activities

Try these additional activities to further explore chemical weathering:

  1. Test other acidic substances like lemon juice or soda on chalk and compare their effects.
  2. Research how acid rain affects buildings and monuments made of limestone or marble.
  3. Investigate how chemical weathering contributes to the formation of caves and sinkholes.
  4. Design an experiment to test how temperature affects the rate of chemical weathering.