Soil Chemistry
Name:
Purpose: The purpose of this activity is to determine if a soil is a Pedalfer or Pedocal
soil.
Soil- a mixture of minerals, organic matter, water, and air that has a definite
structure and composition.
Pedalfer- a soil that has an accumulation of Iron (Fe) and Aluminum (AI). These
soils are also characterized by a lower pH and the presence of silicate rock particles.
Pedocal- a soil that has an accumulation of Calcium (Ca). These soils are often
characterized by a higher pH and the presence of carbonate rock particles. Iron is
not found in Pedocal soils.
Introduction: In this laboratory activity you will perform three different tests on
your soil. In the first test you will test the pH, which indicates whether your soil is
acidic or alkaline. In the second test you will test your soil for the presence of Iron
and in the third test you will test rock particles in your soil to determine if they are
silicates or carbonates
Data table:
pH
Iron test (+ or -)
Acid test (+ or -)
Test 1 pH
1. Place a small amount of soil into a clean test tube. (1/8 full)
2. Fill the test tube with the soil about half full with sink water.
3. Stopper the test tube, place your thumb over the stopper and shake until mixed.
Always keep the test tube pointed away from your classmates.
4. Remove the stopper. Place test tube into the test tube rack and allow soil to settle
to bottom. (5-10 minutes)
5. Dip a small amount of pH paper into the water for analysis.
6. Record your results on the data table provided.
Test 2 Iron Test .
1. Place a small amount of soil into a clean test tube. (1/8 full)
2. (Do not pour HCl from the beaker. If any acid gets onto your skin, rinse with water
and notify your teacher.)
3. With your test tube and soil in the test tube rack, carefully add the 3mI of HCl
(about half full).
4. If the acid reacts with the soil, contact the teacher before proceeding.
5. Stopper the test tube and shake to mix contents. Place your thumb over the
stopper while mixing.
6. Remove the stopper and place the mixture into the test tube rack until the soil
settles to the bottom. (5-10 minutes) .
7. Use your pipette to carefully transfer 10 drops of the clear liquid from above the
soil to a clean test tube.
8. Add ammonia to the test tube until the pH of the solution is greater than 8. (start
with 15 drops) test the pH…still lower than 8? Then add more ammonia and test
again until you get to a pH higher than 8.
9. If iron is present, a reddish-brown precipitate will appear in the solution once the
pH is greater than 8.
Test 3 carbonates or Silicates
1. Place three (3) rock particles from your soil onto the glass plate provided.
2. Use the pipette to carefully place 1-2 drops of HCI onto each particle. .
3. Carbonate particles, which indicate a Pedocal soil will react with the HCl by
fizzing and bubbling. Silicate particles, found in Pedalfer soils, will not react with HCl
Conclusion: Write a brief summary of your results (is your soil pedalfer or
pedocal?) and give your opinion of this activity.