Hard as a Rock

By Pamela Galus and Rebecca L. Kadel


Day 1

Students, individually, are instructed to draw a hydrologic cycle (water cycle). They should include all aspects of the cycle that they can think of. From their individual drawings, students should participate in a discussion of the drawing of a large cycle on a piece of poster board (large paper) to be displayed in the room during this week's activity.

Aspects to include in the drawing

  • Clouds precipitate (rain) and relative humidity are in the atmosphere
  • Rain into streams and ultimately the ocean, evaporation from soil and surface water, transpiration from plant material, sweat and breathing from animals are on the surface
  • Water percolating into the soil (from rain, or animal wastes) to an underground stream, or aquifer are underground sources
  • These are on the bottom of their athletic shoes.....TREDS (T transpiration, R respiration, E evaporation, D drainage through the soil and S storage)

See illustration at http://ga.water.usgs.gov/edu/watercyclegraphic.html

Introduce sources and types of acid rain.

Give each student a watch glass or petri dish to take home. They are to place a small amount of tap water into the dish and leave it sit for two days (until all water is evaporated). Bring this back to school for discussion.

  • What is left in the dish?
  • How did it get there?
  • What if the pH of the water were changed? Would the amount and/or nature of the matter increase or decrease?

Day 2 - Lab

Instructor Information:

Lab Station 1:

(This lab station should have a small amount of steel wool in a test tube with a small amount of water - for rust to occur, this test tube may need to be set up a day or two in advance. In another test tube, place a small amount of steel wool with no water. Also, place a sample of Dakota sandstone. Each sample should be labeled.)

  1. Record observations of the substances in the test tube.
  2. Record two observations on the Dakota sandstone. What elements would be prominent in areas where this sandstone formed?

Lab Station 2:

(This station will have three samples of sedimentary rock such as limestone, shale and breccia, which are labeled and submerged in white vinegar in different beakers. One limestone sample should have a 50 mL beaker with an eyedropper beside it.)

  1. Different types of rock undergo chemical weathering at different rates.
    Examine the three rock samples in the beakers that have been submerged in acid. Is there evidence that any of these samples have undergone chemical weathering? Explain.
  2. Use the eyedropper to place one drop of acid on the dry limestone sample and record your observations.
  3. Is a chemical reaction occurring? Explain.

Lab Station 3:

(At this station, place small rock samples (with a volume of 3 cm3 or less) that have high clay content with test tubes and water.)
Take a small sample of the rock and place it in the test tube. Add 20 mL of water to the rock in the test tube. Place your thumb over the opening and shake the test tube vigorously for several minutes.

  1. Record observations and explain what is occurring.
  2. Set the test tube in the stand and wait a minute. Why does the water remain cloudy?

Lab Station 4:

(Place a sample that shows evidence of ice wedging; could simply be a large rock with several pieces broken off.) Water invaded the cracks of this rock and by alternately freezing and thawing, broke off small pieces.

  1. Has chemical or physical weathering occurred? Explain.
  2. Is the chemical composition of the parent rock the same as the pieces? Explain.

Lab Station 5:

(Place a rock sample -- or several samples -- that has been rounded by running water; river rock.)

  1. Compare this sample with the pieces of rock you saw at lab station 4. How are they different?
  2. What caused the edges of this rock to be rounded?

Lab Station 6:

(Place a rock sample that has a pothole. Potholes form when small rocks are in an indentation in a rock and a wave causes the rock to spin; like sandpaper, the rock drills a hole. To give the students a hint, add a small rock fragment to the hole.)

  1. What caused the hole to form in this rock sample?

Lab Station 7:

(Use a ring stand to suspend a two-liter bottle that has a pin hole in the bottom above a bar of hand soap - or a very soft rock such as one that contains a large amount of chalk or talc. The bottle should provide about a drip a second. The instructor may want to drill a hole in the sample to make it appear that weathering has occurred but the edges should be kept smooth. In this instance, either chemical or physical weathering could be occurring - what matters is the reasoning students use to arrive at their answer which will reflect their understanding.)

  1. Compare this hole to the hole in the rock at lab station 8. Record two observations (how are they alike and different).
  2. Is this chemical or physical weathering? Explain.

Lab Station 8:

(Place rock that has a plant growing in the crack. The instructor may need to find a rock with a crack and place a plant in it.)

  1. Over time, would you expect this crack in this rock to become larger or stay the same? Explain.
  2. Is this chemical or physical weathering? Explain.

Lat Station 9:

(At this station, there should be two set ups exactly the same with a two-liter bottle on a ring stand that is dripping water at a rate of approximately one drop per second. Cut off the bottom (about 4 cm from bottom) of another two-liter bottles to make a funnel and place a piece of filter paper in the funnel. Invert and suspend the funnel from a ring stand ring below the dripping water. Below the funnel, place a beaker that is large enough to catch the water. Students will need wide range pH paper that goes from 1 to 14, or from 7-14. This station should be set up an hour or so prior to the activity and if necessary, the cap can be used to slow the water down in the funnel so that the samples will be saturated. One funnel should be filled with sandstone and the other will be filled with limestone that has been crushed so that the grain size is approximately equal to the sand.)

  1. You will test the pH of the water going into and out of both the sample of limestone and sandstone. Predict whether or not the pH of water will be changed in each sample. Record your predictions BEFORE you proceed.
  2. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping water in the top two-liter bottle in sample 1. Record the pH.
  3. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping beneath the funnel in sample 1. Record the pH.
  4. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping water in the top two-liter bottle in sample 2. Record the pH.
  5. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping beneath the funnel in sample 2. Record the pH.
  6. If there was a difference between the two pH readings, explain why the difference occurred. (If there was no difference, explain why the pH didn't change.)

Lab Station 10:

(At this station, there should be three rock samples that are very different labeled 1, 2 and 3. There will also be one soil sample in a petri dish that is open for students to touch. The soil should have tiny fragments from one of the rock samples mixed in. It should be very obvious which rock produced the fragments that are mixed in the soil.)

  1. Which rock sample was most likely in the area when this soil formed? Explain how you know.
  2. How might the soil in an area be impacted by the type of rock in an area? Explain.

Student Copy:

Background:

Weathering involves the break-up of rocks. There are two main types of weathering, mechanical and chemical weathering.

Mechanical weathering occurs when rocks split into smaller pieces; the smaller pieces have the same chemical composition as the parent rock. One way mechanical weathering occurs is ice wedging. When water freezes in the cracks of rocks it can take up 10 percent more space; alternating freezing (expanding) and thawing (contracting) cause the rocks to split further. Another way mechanical weathering occurs is by repeated wetting and drying which breaks up rocks that contain clay since clay swells when it is wet. Small plants can also grow in the cracks of rocks and the roots may split the rock. In a process called exfoliation, large sheets of exposed rock break away sometimes forming rounded mountain peaks.

Chemical weathering occurs when rocks are changed into something different; the rocks are changed chemically. Chemical weathering results mostly from the action of rainwater, oxygen, carbon dioxide and plant decay. When rocks react chemically with water it is called hydrolysis. Oxidation occurs when oxygen reacts chemically with substances in rocks. When rain moves through the atmosphere, it combines with other substances and can form a weak acid. When rain reacts with carbon dioxide it forms carbonic acid, which acts on many minerals (feldspar, hornblende, augite, biotite mica) dissolving elements out of the rock, which changes the original rock into a clay mineral. Some other minerals such as calcite, dissolve completely while others such as gypsum and halite dissolve slowly. Acids also form when plant and animal material are dissolved in rainwater.

Mechanical and physical weathering are two distinct categories but they rarely occur alone. A rock sample may be broken into smaller pieces (mechanical weathering) and then chemical weathering may act on the pieces to change them into something completely different.

Lab Station 1:

Record observations of the substances in the test tube.

  1. Record two observations on the Dakota sandstone. What elements would be prominent in areas where this sandstone formed?

Lab Station 2:

  1. Different types of rock undergo chemical weathering at different rates.
    Examine the three rock samples in the beakers that have been submerged in acid. Is there evidence that any of these samples have undergone chemical weathering? Explain.
  2. Use the eyedropper to place one drop of acid on the dry limestone sample and record your observations.
  3. Is a chemical reaction occurring? Explain.

Lab Station 3:

Take a small sample of the rock and place it in the test tube. Add 20 mL of water to the rock in the test tube. Place your thumb over the opening and shake the test tube vigorously for several minutes.

  1. Record observations and explain what is occurring.
  2. Set the test tube in the stand and wait a minute. Why does the water remain cloudy?

Lab Station 4:

Water invaded the cracks of this rock and by alternately freezing and thawing, broke off small pieces.

  1. Has chemical or physical weathering occurred? Explain.
  2. Is the chemical composition of the parent rock the same as the pieces? Explain.

Lab Station 5:

Compare this sample with the pieces of rock you saw at lab station 4. How are they different?

  1. What caused the edges of this rock to be rounded?

Lab Station 6:

  1. What caused the hole to form in this rock sample?

Lab Station 7:

Compare this hole to the hole in the rock at lab station 8. Record two observations (how are they alike and different).

  1. Is this chemical or physical weathering? Explain.

Lab Station 8:

  1. Over time, would you expect this crack in this rock to become larger or stay the same? Explain.
  2. Is this chemical or physical weathering? Explain.

Lab Station 9:

  1. You will test the pH of the water going into and out from both the sample of limestone and sandstone. Predict whether or not the pH of water will be changed in each sample. Record your predictions BEFORE you proceed.
  2. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping water in the top two-liter bottle in sample 1. Record the pH.
  3. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping beneath the funnel in sample 1. Record the pH.
  4. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping water in the top two-liter bottle in sample 2. Record the pH.
  5. Take a piece of pH paper that is about 2 cm long. Place the strip under the dripping beneath the funnel in sample 2. Record the pH.
  6. If there was a difference between the two pH readings, explain why the difference occurred. (If there was no difference, explain why the pH didn't change.)

Lab Station 10:

  1. Which rock sample was most likely in the area when this soil formed? Explain how you know.
  2. How might the soil in an area be impacted by the type of rock in an area? Explain.

Day 3

Place students in small groups (3-4) to brainstorm on the influence that increasing greenhouse gases, resulting in change in acid rain, will have on (1) earth's surface (rocks), (2) society (cultures) and (3) economics (import, export, crops, clothing, housing, etc.). Specific aspects to look at would be temperature increase, changes in global wind patterns, and changes in global precipitation.
If you preferred, this could even be divided into smaller groups, each group brainstorming one of the above numbered topics and then, as an entire class, make on big "concept map"
With either method used, there should be a concluding map with all of the class' ideas included. This will be very messy, with arrows going every which way!!!

This is only a tiny example of the interconnectedness of the systems of the world to a change in the production of greenhouse gases.


Day 4

The instructor should ask students to help generate a list of questions generated from the learning so far. What would students like to know more about? How weathering impacts soil?
For example:

  • How does 'acid' rain effect how soil forms?
  • For places that have different types of rocks (granite, limestone, sandstone), which areas will be most affected if the pH of rain continues to decline?
  • What do the rocks in an area have to do with the composition of lake water?
  • What impact do manmade structures have on acid rain (if the water runs through gutters, will the pH change)?
  • What impact does weathering have on your own school building?

The instructor should allow a time at the end of the discussion to begin allowing students to discuss with their team how a valid experiment could be conducted to find evidence to support a question that interests them. Students will, of course, be limited to obtainable equipment. The activities should be timed so that all necessary supplies are in the classroom on Friday, ready to be set up on Monday. Students who will be growing plants need to start their labs on Friday as it takes three days for parakeet seed (which is what we recommend you use since it is inexpensive and easily obtainable) to germinate.

The requirements for this assignment are:

  1. Students need to present their plan to the class orally and critique each other's design. Begin by stating your title and hypothesis. Each design has to follow proper scientific procedure; the group must state their hypothesis and their plan to control variables. The group should be able to explain how the independent variable was expected to impact their experimental group and how their dependent variable would respond.
  2. Each group needs to have some way to collect data that can be displayed graphically.
  3. The students should write up their laboratory activity to communicate their results, present their findings orally to the class, and suggest further experimentation that could be conducted by next year's students as a follow-up.

The following is one example of a student created lab:

Hypothesis:

If 50 mL of an aqueous solution with a pH of 5 is poured into 500 mL of soil that contains 50 grams of limestone, the water that drains through the soil will have a pH of 7.

This team of researchers used two plastic, 500 mL beakers. In both, they placed the exact same amount of soil, collected from the same place at the same time. In their experimental group, they added limestone chips to the soil and nothing was added to the soil in the control group. Holes were punctured in the bottom of both plastic beakers (the same size in the same place) and the beakers were set inside another 500 mL plastic beaker so that the water would be captured in the bottom container. The students added the acid solution to the experimental beaker, the same amount of distilled water to the control beaker, and then tested the pH of the fluid that was captured after moving through the soil in both beakers. The purpose of this experiment was to determine if the limestone found naturally in the soil and around lakes in our area was actually protecting our waters from drastic changes result from rain with a lowered pH. Students designed this experiment because we do not have massive fish kills in our area as one would expect if the pH changed drastically after a heavy rain and the most likely reason is because something in the soil neutralizes the acid (and that something could be limestone).

Assessment:

Assessment of the discussion is informal. The instructor should only identify potential problems and attempt to guide students but should not provide solutions. If the students do not correct problems in experimental design in advance, they should be allowed to attempt the experiment and discover the problems as they progress.


Day 5

Student Information:

You will present your experimental design to the class for a critique. You should prepare a brief synopsis of your experiment including the title, hypothesis, brief description of your planned experiment including your control and experimental groups, your independent variable, how you will control other variables, and the anticipated results.

As the process commences, the receiver must realize that the other class members are trying to help. However, some individuals are better than others at providing feedback; the feedback should be positive and focus mainly on the strengths of your design. You are in control of the feedback session. That is, you may call on whomever you wish (since everyone is required to raise their hand to request permission to speak) and you may end the feedback session when it ceases to be useful to you, when you begin to feel angry or frustrated, or when, for whatever reason, you have decided that the feedback is no longer useful. Plan for about five minutes; the instructor will cut in when the time has elapsed or when it appears that things have reached a climax.

If you would like negative feedback from the class, you should specifically request it. You may want to ask something like, "How can I improve my hypothesis?" or "Can anyone think of a variable that I haven't considered?" You need not agree with the replies, take the information you want and leave the rest - just accept them all with a polite nod, thank your classmates for their help, and move on when you have what you need.

From the instructor, you will receive the following:

  • Name of team members:
  • General Plan:
  • Variables controlled:
  • Variables not controlled:
  • Strengths:
  • Things to consider:

After students have constructed their final experimental design, the instructor should determine and provide students the following:

  • Name of team members:
  • General Plan:
  • Variables controlled:
  • Variables not controlled:
  • Strengths:
  • Things to Consider:
    • Hypothesis stated correctly
    • Feasibility of experimental design
    • Data collection technique
    • Control present

Day 6

You will correct any errors in your experimental design and review the process of science. YOU must give a list of the materials you will need for your lab to the instructor TODAY (this is your responsibility and you are accountable for any materials you do not ask for). You may need to purchase unusual items yourself. Everything needed for the lab must be in this room tomorrow. If you will be growing plants, they should be started the Friday prior to the activity, as three days are required for germination.


Day 7-11

You will set up your lab and record data for five full days. EACH student must keep a record of the results; if you have no data, you have nothing and will need to repeat the experiment.

Instructions for Formal Laboratory Write-up: As you work on the written portion, remember that the purpose of the laboratory write-up is to inform the reader of your results and allow them to set up the experiment the exact same way and get the exact same results.

  • Title: The title of your experiment should be informative; it reveals the content of the Experiment.
  • Hypothesis: Remember that a hypothesis is a testable statement. It must be a concise, accurate, informative statement that suggests the experiment. The hypothesis is often posed as an 'if …. then' statement.
  • Materials: This section must include a complete list of the supplies the researchers used to perform the experiment from beaker size to solution amount.
  • Procedure: In the procedure, explain exactly what you did and how you did it (step by step); include amounts, size and materials used. Assume your reader has no idea how
    to perform this experiment. You must identify the variable and state how they were controlled. You must also state how you controlled your experiment. The reader must know what data you collected and how it was collected. This section does not contain data.
  • Data: This section has just the facts; just data, no analysis, no conclusions. Include
    your observations, measurements, charts and graphs.
  • Analysis and Conclusion: What was the result? What did you learn? If there were problems, identify and explain them. Never alter data; if something went wrong just
    explain what it was and how the problem should be corrected. What went well? Did you prove or disprove your hypothesis? Keep in mind that not all hypotheses will be correct. Finally, explain what you have learned as a result of the experimentation.

Resources that are helpful to locate background information:

  • National Atmospheric Deposition Program
  • Environmental Protection Agency
  • United States Survey Division