Earth Science Lab - Porosity

Recommended Grade Level: Middle School

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There are many objects in nature that appear to be non-porous, like a solid rock. However, this is not always the case. Many rocks are actually years of particles compressed together eventually forming a rock - but leaving tiny spaces between these particles. This creates pores in a rock, much like those in a sponge, but much smaller and mostly invisible.

Challenge your students to think more about the world that surrounds them. Rocks are generally considered solid objects, but after investigating more closely, students can discover how pores in these rocks leave more room than you might suspect.

This lab requires only a few supplies: small rocks, sand and soil, 3 500 ml beakers, 100 ml graduated cylinder and some water. As always, please be sure to supervise this activity, as lab safety is very important.

1. Getting Started

Start by filling each beaker to 350 ml with small rocks, sand and soil. Now fill your graduated cylinder with 100 ml of water.

2. Testing your Materials

Next, pour the water into the beaker of rocks until the water reaches the top of the gravel. Be sure to record how much water it took to reach the top of the gravel (if more than the 100 ml of water is needed be sure to record the additional amount used). Do the same for each beaker of sand and soil, carefully recording your observations.

3. Calculations and Conclusions

In groups, or as a class, calculate the percentage of porosity per material using the following equation: (x ml water used)/(350 ml of material in beaker) = y(100) = y % Discuss results as a class.

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