Porosity and Permeability: classroom activity directions

Are you teaching your students the difference between porosity and permeability? While these two properties of soils and rocks are related, they are not the same! And what better way to understand the difference between porosity and permeability than a hands-on lab activity!?

In this lab experiment, compare the porosity and permeability of three sediments: gravel, sand, and clay/silt. These activities are easy to complete with common household items.

In this post, you will learn how to set up a porosity and permeability activity in your classroom. You can also get print-formatted versions of these directions, worksheets, handouts, and classroom posters to use during this lab in my Soil Science Unit!

Pre-lab Activity

Place a small amount of each sediment on three trays. Allow students to examine and touch the sediments. Ask students to consider:

Rub the material between your fingers. Describe how it feels. Coarse? Gritty? Fine? Sticky? Stiff? Loose?
Describe the material. Can you see individual grains? How large are they? What color(s) do you see?
Make a prediction: Which soil sill have the highest porosity? Which will have the lowest porosity?
Make a prediction: Which soil sill have the highest permeability? Which will have the lowest permeability?

Gather Your Materials

Gather the following materials for the demo. You will need:

Porosity Lab Activity Materials:

Dry gravel (~100 mL)
Dry sand (~100 mL)
Dry silt or clay (~100 mL)
3 small containers of equal size (e.g., 150 mL beakers)
Extra beaker or liquid measuring cup
Water
Student lab handouts (1 set per student)

Permeability Lab Activity Materials:

Dry gravel (at least 100 mL)
Dry sand (at least 100 mL)
Dry silt or clay (at least 100 mL)
Graduated cylinder (200 mL or larger)
400+ mL funnel to sit atop the graduated cylinder
3 filter papers (e.g., pieces of coffee filters)
Scissors
Permanent marker
Beaker or liquid measuring cup
Water
Stopwatch
Student lab handouts (1 set per student)

Directions

Porosity Directions:

Pass out the materials to the lab groups.
Demonstrate the method with the gravel: Measure ~100 mL of gravel into a container and gently shake the container so that the surface of the gravel is flat.
Record the total volume of the gravel on the lab worksheet.
Fill a beaker with 100 mL of water.
Slowly and gently, pour the water into the gravel, until the water level reaches the surface of the gravel.
It may take some time for the water to “soak through” to the bottom of the beaker. You may need to pour a little water at a time and then wait before pouring some more.
Record the volume of the pore space. This is equal to the volume of water you poured into the gravel.
Students will repeat the procedure with the sand and the silt/clay.
After students collect their measurements, show the students how to calculate the porosity:

Permeability Directions:

Pass out the materials.
Demonstrate the method with the gravel: Balance the funnel on top of the graduated cylinder and place a filter paper into the funnel to cover the stem hole.
Fill the funnel approximately half way up with gravel. Do not fill the funnel all the way up to the top.
Tap the funnel lightly to make the surface of the gravel flat.
Use the marker to mark the level of the surface of the gravel on the funnel.
Put 200 mL of water in the beaker or measuring cup.
Start the stopwatch as you pour all 200 mL of water over the gravel.
At regular intervals, record the time and the volume of water in the graduated cylinder.
The water may pass through some sediments very rapidly. You may only have time to record a few volume measurements before the water is done passing through.
After students finish the procedure with the gravel, they will repeat the procedure with the sand and the silt/clay. Fill the funnel to your previous mark with the other sediments.
Look at the recorded data. Which sediment did the water pass through most quickly? This soil has the highest permeability.

Reflection Questions

In your own words: what is the difference between porosity and permeability?
What are some possible sources of error in the porosity lab?
What are some possible sources of error in the permeability lab?
During rain, water seeps down into the soil through its pores. Which soil will water pool on top of first: a soil with high permeability or a soil with low permeability. Which size grains would this soil likely have a lot of?
You are potting a plant that needs a soil with high porosity. What size grains might help give a soil a high porosity?

This lab comes from my Soil Science Unit!

Your students will love the illustrated learning materials, plus you’ll support Wild Earth Lab with your curriculum purchase!