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Learning Objectives Model chemical weathering
Distinguish two weathering processes Associate soil with source weathering processes Introduction
Any object which is exposed to weather - even rocks - changes after contact with rain,
wind, and natural processes. When rock changes from its original composition
through chemical, physical, and biological processes, it has been subjected to
the weathering process. Unlike the physical and chemical alteration of rock through
heat-inducing metamorphism, weathering disintegrates or alters rock in its original
location. Often subtle, usually slow, weatherization sculpts rocks and builds new
landforms while tearing down old ones. Weathering usually occurs at the Earth's
surface where exposed rock meets the atmosphere. However, because water can
penetrate the Earth's crust through cracks, fissures, and microscopic holes,
weathering also can take place deep underground. © 2014 eScience Labs, LLC.
All Rights Reserved Chemical weathering affects almost all types of
rocks, especially those with greater amounts of
exposed surface area and rocks subjected to
water. Rocks also usually disintegrate faster in
warmer temperatures because heat triggers
chemical reactions that break apart bonds holding
rocks together. Basically, this is what chemical
weathering does: it breaks the bonds holding the
rocks together causing rocks to fall apart.
Therefore, rocks in warm temperatures with a lot
of rainfall weather more quickly than rock in cold
polar regions. Figure 1: Erosion, as seen here, is a form
of weathering. In any type of chemical weathering, ions are removed or exchanged from minerals,
resulting in either new minerals or destruction of minerals. Note the following
examples of chemical weathering: Oxidation: Oxygen combines with rock minerals. Example: Iron, a common
mineral in rocks, becomes red or rust colored when oxidized.
Hydrolysis: Water combines with rock minerals. Example: A hydrogen or other
ion found in water will exchange with another mineral ion. Silicate minerals in
rocks, during the exchange, can turn into clay minerals.
Dissolution: Water removes ions. Example: If a rock has the mineral halite,
water will dissolve the halite.
Carbonation: Carbon dioxide interacts with water and minerals and forms
weak carbonic acid that dissolves rock, making pits and furrows or even
sinkholes, caves, and caverns. Example: Rainwater with dissolved carbon
dioxide from the atmosphere creates a weak carbonic acid, the most abundant
natural acid on Earth, that wears on rock, particularly limestone. Fossil fuel
burning fuels add nitrogen and sulfur into the atmosphere that strengthen the
environmentally-damaging carbonic acids (acid rain). Knowledge Check
In any type of chemical weathering,
what
is removed
or exchanged from minerals?
© 2014
eScience
Labs, LLC.
All Rights Reserved Pre-Lab Questions
1. List at least three factors that can increase the rate of weathering in rocks. 2. Two internationally-renowned rock climbing areas have limestone rock. El Chorro is in
mainland Spain, and has a dry climate with little precipitation. Tonsai is a beach on
© 2014 eScience Labs, LLC.
All Rights Reserved the coast of Thailand; here, the rock is constantly exposed to moist, salty air. Which of
these climbing areas is known for having fragile rocks that can break and endanger
climbers? Use you knowledge of weathering to explain this phenomenon. 3. What chemical weathering process is linked to the formation of sinkholes, caves, and
caverns? Explain how. 4. What is contained in soil? Experiment 1: Speleology: Understanding Cave Formation
Caves are found all over the world and contribute to a variety of biological and environmental
phenomena. Caves are comprised of a variety of substances, but often contain limestone. In
this experiment, you will view the effect of chemical weathering on limestone and apply that
impact to caves on Earth. Materials 100 mL of Acetic Acid (vinegar, an acid with a
pH of 3), C2H4O2
(3) 250 mL Beakers
100 mL Carbonated Water
2 Chalk Pieces (made of limestone, a naturally
occurring material), CaCO3
Permanent Marker Scale
3 Seashells
*Stopwatch
*100 mL Water, H20
*You Must Provide Procedure
© 2014 eScience Labs, LLC.
All Rights Reserved Part 1
1. Use the permanent marker to label the first beaker as "Water," the second beaker as
“Carbonated Water,” and the final beaker "Vinegar."
2. Pour 50 mL of each liquid into the corresponding labeled beaker.
3. Use the scale to determine the mass of each beaker. Record the initial mass in Table 2.
4. Break two pieces of chalk in half so that you have four pieces of chalk.
5. Place one small piece of chalk in each beaker. Weigh and record the new mass of the
beaker in Table 2.
6. Determine the mass of each piece of chalk by subtracting the mass of the beaker
from the mass of the beaker + chalk. Record your data in Table 2.
7. Formulate a hypothesis to predict what will happen to the chalk in each cup. Record
your hypothesis as the answer to Post-Lab Question 1.
8. Add one piece of chalk to each beaker. Immediately begin timing the reaction. After
one minute, evaluate the beakers and record your observations in Table 3. Continue
to observe the beakers for five minutes, and record all observations in one minute
intervals.
9. Thirty minutes after adding chalk to each beaker, re-mass each beaker on the scale.
Record the final mass values in Table 2.
10. Calculate the change (Δ) in mass for each piece of chalk by subtracting the initial mass
from the final mass.
11. Calculate the percent change in the mass using the following formula:
(Δm/mi ) 100 where Δm = change in mass and mi = initial beaker + chalk mass.
Record your percent change answers in Table 2. Table 2: Part 1 Experiment Data
Beaker Beaker
Mass (g) Initial Beaker
+
Chalk
Final Beaker + Δ Mass
Δ Mass (%)
Chalk Mass Mass (g) Chalk Mass (g)
(g)
(g) Water
Carbonated
Water
Vinegar © 2014 eScience Labs, LLC.
All Rights Reserved Table 3: Beaker + Chalk Observations
Time (minutes) Water Carbonated Water Acetic Acid 1
2
3
4
5 Part 2
1. Rinse out the beakers used in Part 1. Pat them dry with a towel or allow them to air
dry.
2. Repeat Part 1, Steps 2 - 10. This time, use a seashell rather than a piece of chalk.
Record your data and observations in Tables 4 and 5. Don’t forget to record a
hypothesis stating what you predict will happen to the seashell when placed in each
beaker; record this in Post-Lab Question 2. Table 4: Part 2 Experiment Data
Beaker Beaker
Mass (g) Initial Beaker Shell Mass Final Beaker + Δ Mass
Δ Mass (%)
Shell Mass (g)
(g)
Shell Mass (g)
(g) Water
Carbonated
Water
Vinegar Table 5: Beaker + Seashell Observations
Time (minutes) Water Carbonated Water 1
© 2014 eScience Labs, LLC.
All Rights Reserved Acetic Acid 2
3
4
5 Post-Lab Questions
1. Record your hypotheses from Part 1, Step 7 here. 2. Record your hypotheses from Part 2 here. 3. Compare and contrast the reaction of chalk pieces in each of the lab liquids. 4. Based on this experiment, explain how a limestone cave forms. Incorporate the
following terms in your description: chemical weathering, carbonic acid, calcite 5. How is the effect of a weak acid on a seashell and chalk related? 6. What environmental factors could affect rates of weathering where you live? © 2014 eScience Labs, LLC.
All Rights Reserved Experiment 2: Rocks into Soil
pH is a commonly measured factor in soil analysis and can reveal information about the
organic and inorganic content of the soil. For example, high concentrations of aluminum and
manganese can significantly lower a soil’s pH. Conversely, if a soil is rich in calcium or sodium
carbonate minerals, it will be basic. In this activity, you will measure the pH of soil and
observe chemical reactivity. Materials 100 mL Acetic Acid (Vinegar), C2H4O2
(3) 250 mL Beakers
2 T. Calcium Bicarbonate (Baking Soda),
NaHCO3
100 mL Graduated Cylinder
Permanent Marker 200 mL Soil Sample
*100 mL Water, H20
*You Must Provide Procedure
1. User the permanent marker to label each beaker as “Sample 1,” Sample 2,” or
“Sample 3.”
2. Transfer one-third (approximately 70 mL) of the soil sample into each beaker.
3. Mix baking soda into Sample 1. Baking soda is a basic (alkaline) material. Observe the
results, and consider what that means. For example, if the sample fizzes, is it likely to
be acidic or basic? Record your observations and conclusions in Table 6.
4. Use the 100 mL graduated cylinder to measure and pour 30 mL acetic acid to Sample
2. Observe and record your conclusion in Table 6.
5. If you did not observe a visible reaction in Step 3, proceed by adding 30 mL water to
the Sample 3. Observe the results, and consider what they mean. For example, what
can you infer about the pH of the soil if neither sample displays a visible chemical
reaction? Record all observations and conclusions in Table 6. © 2014 eScience Labs, LLC.
All Rights Reserved Table 6: Soil + Acid and Water Observations
Sample Observations 1
(Soil + Baking Soda )
2
(Soil + Acid)
3
(Soil + Water) Post-Lab Questions 1. Acidic soil may require the addition of lime, and alkaline soil benefits from organic
matter such as decomposed tree leaves. What would your soil require to be more pH
balanced? 2. Extension activity: Local Cooperative Extension offices affiliated with land-grant
universities often test soil samples for pH for free. Consider having one test your soil
or obtaining a soil examination kit from a hardware store or gardening store. What
type of results did they provide? Did the data surprise you? Explain your answer. © 2014 eScience Labs, LLC.
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