Chemical Weathering Lab
Background Information: (Summarize for your lab notebook)
Weathering is a slow, continuous process that breaks rocks at or near the earth’s surface
in response to air, water, living matter, and the force of gravity. Chemical weathering, or
decomposition, is one such process where chemical reactions take place between original
earth materials and water, carbon dioxide, oxygen, and acids. These chemical reactions, in
effect, alter the internal structure of the original minerals in the parent rock. As a result, both
the chemical composition and physical appearance of the rock are changed. Chemical
weathering can involve a number of processes including oxidation, carbonation, and the
creation of plant acids. The rate at which rock materials chemically weather will depend upon
such things as particle size, mineral composition, climate, and level of exposure to plant and
animal activity.
Problem/Objective: Which of the four rock samples below with weather the most in 16 days
(A classes) /15 days (B class)?
Pre-lab Questions:
1. Create and fill in the table below as you think about each of the rock samples.
Sample
Rock Type
Composition
Predicted Change
Marble
Limestone
Sandstone
Granite
Hypothesis:
Write a hypothesis stating which rock sample above you think will chemically weather the
most. Write your hypothesis in the “if…then…because” format.
Materials:
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4 groups of rock samples
glass jars, 8 oz.
graduated cylinder, 100mL
strainer
triple beam balance
water
dilute hydrochloric acid
Procedure:
1. Place a couple of rock pieces of each type in four separate jars.
2. Determine the mass of each jar and record on your data table.
3. Label each jar with the rock type and your names.
4.
5.
6.
7.
Ask the instructor to cover your rocks with dilute hydrochloric acid.
Place your jars on the tray provided. Let sit overnight.
Drain each sample and determine the mass. Record.
Repeat steps 4-6 for 3 days.
Data: Create this data table in your notebook. Include a title.
Rock Sample
Combined Mass
Day 1
Combined Mass
Day 16 (A classes)
Day 15 (B class)
Net Change
(1-3)
Total Mass
Lost
Data Interpretation: Create an appropriate graph using the total mass lost for each rock
sample using the graphing website link. Make sure there is a title, x/y labels and units.
Print the graph, fold in half and staple in your lab notebook.
Data Analysis and Conclusion: Answer the following questions in full sentences in your lab
notebook.
1. Create this table in your notebook:
Chemical Weathering Class Averages
Rock Type
Average Mass Lost
Marble
Limestone
Sandstone
Granite
2. Refer back to your hypothesis. Was it correct? Why or why not?
3. By studying the class average table, discuss the results for each sample. Include which
lost the most and the least and why.
a. Marble:
b. Limestone:
c. Sandstone:
d. Granite:
4. What properties of the samples may have affected the varying resistance to chemical
weathering? What do you think was the most significant?
5. What type of chemical weathering does this exercise most closely simulate?
6. If you were asked to select a building stone to be used in constructing the exterior of
a new office building in a city with heavy industrial emissions and car exhaust, which
of the four samples you tested would prove most durable in this environment? Why?
7. List examples of chemical weathering you may have observed on your school grounds,
and describe what processes may have been responsible for each example.