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Mechanical and Chemical Weathering - DOC

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Mechanical and Chemical Weathering - DOC Powered By Docstoc
					                             Weathering Lab
Name: ______________________ Date: ___________ Instructor: ________________

                     Mechanical and Chemical Weathering
Objectives:

              To model mechanical and chemical weathering processes
              To record, analyze and compare data from the different models

        As you know from your reading, weathering is the break-up of rock resulting
from exposure to the earth’s atmosphere. Weathering occurs due to either mechanical or
chemical processes. Mechanical weathering takes place when rocks are broken apart by
physical activities such as ice wedging or biological actions of plants and animals.
Chemical weathering is generally caused by hydrolysis, oxidation or dissolving-chemical
reactions that alter and break down rocks. In this lab, you will conduct two separate
weathering experiments. Part One will model mechanical weathering using limestone
gravel. Part Two will model chemical weathering of the same material under both warm
and cold conditions.
        Erosion plays an important role in the weathering process. By transporting
weathered material away, erosion exposes new surface area to weathering agents. In
these experiments, the erosion process will be modeled in the rinsing procedures. In Part
1, using a plastic screen while rinsing establishes a protocol for what size material would
be eroded away in your model.


                                Part 1: Mechanical Weathering

Procedure: Caution! Read entire procedure before continuing!

       1. Fill a 250ml beaker to about the 200ml level with limestone gravel.
       2. Rinse with water and drain while covering the top of the beaker with a plastic
           screen. Use a paper towel to absorb excess moisture.
       3. Obtain mass of empty plastic bottle (without the cap) using digital scale.
          Record in data sheet.
       4. Add gravel to plastic bottle. Re-mass and record data. Subtract mass of
          empty bottle to obtain mass of gravel. Record this mass as well.
       5. Cap bottle and shake vigorously with a consistent rhythm for 10 minutes.
       6. Re-rinse gravel in the plastic bottle, making sure to get any material that sticks
          to the cap back in the bottle. Again, use the screen to sort which material will
          be rinsed away.
       7. Re-measure the mass of the bottle with gravel. Record in data sheet.
       8. Empty, rinse and dry the bottle. Re-mass to determine whether there has been
           any change in mass for the bottle. Record in data sheet.
       9. Subtract final gravel mass from initial gravel mass and record. This is the
          mass of the material weathered away in this experiment.
                                    Weathering Lab


Prediction Questions:

What factors do you think will affect the rate of weathering in your model?



What protocol can your group implement in order to ensure a consistent rate of
weathering?



How could you change the experiment to test for these variables.(Lack of consistent rate.)




     PART 1 DATA TABLE             Initial Mass   Final Mass     Change in Mass
     Bottle
     Bottle and Gravel
     Gravel                        mi =           mf =           m =

Using the following formula determine the percent change of material in the weathering
model above: (m/mi )100 where m = change in mass and mi = initial mass.




                            Part 2: Chemical Weathering

Procedure: Caution! Read entire procedure before continuing!

       1. Obtain four, clean, dry beakers. Label one beaker “C,” one beaker “C
           Control,” one beaker “W” and the last “W Control.”
           Measure the mass of each beaker and record to data table.
       2. Fill each beaker up to the 50ml level with rinsed and dried marble gravel.
       3. Re-measure and record the mass for each sample.
       4. Fill beaker C with enough cold vinegar to completely cover the gravel.
          Repeat procedure for beaker W using warm vinegar.
       5. Fill beaker “C Control” with enough cold water to completely cover the
           gravel. Repeat procedure for “W Control” using warm water.
       6. Place beaker C and C Control in the plastic basin of ice water and beaker W
          and W Control in the plastic basin of warm water. Allow each sample to
          react for 20 minutes. Gently swirl each beaker every minute. While you wait,
          answer prediction questions.
       7. Re-rinse and dry each sample, taking care not to lose any gravel.


                                            2
                                    Weathering Lab


       8. Measure and record the mass of each sample.
       9. Subtract final mass from initial mass. Enter this on data sheet.
       10. While the experiment progresses, observe and record any differences you
           notice in the beakers.

Prediction Question:

Based on your understanding of earth science, which sample do you expect will weather
more? Why?




DATA            Mass of    Initial Mass     Mass of       Final Mass of   Change in
TABLE           Beaker     of Beaker        Gravel (mi)   Beaker and      Mass (m)
                           and Gravel                     Gravel
Sample C
Sample W
C Control
W Control


Analysis and Conclusion:

Using the following formula determine the percent change of material in each of the
weathering models: (m/mi )100 where m = change in mass and mi = initial mass.




Based on your calculations which model had the highest rate of weathering (Include your
data from part One.)?




Based on your observations, what factors affect rates of weathering?





                                            3
                                     Weathering Lab




Describe an environment that you would expect to have a high rate of weathering.




Describe an environment that you would expect to have a low rate of weathering.




List the environmental factors that affect rates of weathering in our region and explain
how each affects weathering rates.




How do your lab results compare with other lab groups?




Discuss possible sources of error in your lab.




Discuss any difference between your prediction in Part Two and your results in Part Two.




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