Chemical Weathering (Nadia Chocron)


Research Question and Hypothesis

How do rocks become weathered chemically?

If acid is applied to rock, then the rocks will show evidence of weathering by decreasing in mass.  

Standards

6.2

Topography is reshaped by the weathering of rock and soil and by the deposition and transportation of of sediment.  

Experimental Design

Rocks that contain carbonate are weathered when exposed to acids.  Not all rocks and minerals have carbonates.  When carbon dioxide is dissolved in water, Carbonic acid s formed.  Carbonic acid builds up on rocks and can lead to chemical weathering.  Certain rocks will be weathered by the carbonic acids creating caverns.  


Independent variable

The independent variable is time of exposure.  Time will be measured by days.  

Dependent variables

The dependent variable is the mass of the rocks.  The mass will be measured by using a digital scale.  

Series

The series will be the type of acid being tested.  We will use vinegar and 10% Hydrochloric acid.  

Constants and Controls

For a control, there will be each type of rock sitting in pure distilled water.  

For a constant, the same amount of liquid and rock will be placed in the container.  

Materials

  • 9 small containers or test tubes
  • labeling tape
  • 3- 15 g samples of granite
  • 3- 15 g samples of marble
  • 3- 15 g samples of pyrite
  • 10 % HCl solution
  • White vinegar
  • distilled water
  • digital scale

Procedures

1.  Place a 15 g sample of each rock type in a container with 50 mL of distilled water.  Label with tape.  

2.  Place a 15 g sample of each rock type in a container with 50 mL of HCl.  Label with tape.  

3.  Place a 15 g sample of each rock type in a container with 50 mL of vinegar.  Label with tape.  

4.  Place all samples in the same place in the classroom and allow to sit for 1 day.  after 1 day, record observations about the appearance of the solution.  

5.  After 2 days, rinse the rocks with water and measure on a digital scale.  Record measurements and replace in containers with fresh liquids.  Each liquid should be 50 mL.  Repeat every 2 days for a total of 10 measurements (including initial mass). 

6.  Graph results.   

Sample data and graphs

Chemical Weathering


Pyrite


Granite


Marble 



Analysis & Conclusions

1.  What did you notice about the weathering of the different rock types?
2.  Which rock was weathered the most by the acids?
3.  Which acid had the biggest effect of weathering?
4.  What did you notice about the rocks versus the mineral?
5.  What acid would likely erode marble in nature?

Photos 

This is the set up of the rocks in the two different acids.

This is pyrite in vinegar on the left and Hydrochloric acid on the right.  

This is marble in vinegar on the left and Hydrochloric acid on the right.  

This is granite in vinegar on the left and Hydrochloric acid on the right.  

References

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