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:

·  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.  Ask the instructor to cover your rocks with dilute hydrochloric acid.

5.  Place your jars on the tray provided. Let sit overnight.

6.  Drain each sample and determine the mass. Record.

7.  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.