Chemical Weathering Lab. 4th grade PSI

Transcription

1 Chemical Weathering Lab 4th grade PSI Teacher s Notes: Having students conduct Mohs Hardness Test requires a lot of preparation. Rock samples and the materials used to test them need to be collected and ready. Divide students for this activity however you think will work best and depending on the number of supplies you have. Make sure you are very familiar with the procedure of the Mohs Hardness Test before you lead this lab, so you will be able to circulate and help students as they work.

2 Chemical Weathering Lab Name: 4th grade PSI Lab Question How does chemical weathering affect different types of rocks? Before You Begin How might carbonated water be like acid rain? Purpose: During this experiment, you will create a model of chemical weathering. This experiment will span two class periods but at least four days; the first day you will create your model and take some measurements, and the second day of the experiment you will take more measurements after you have waited for the chemical weathering to occur. While you are conducting the lab, make sure to fill out the charts for Mohs Hardness Test as you work. There are separate charts for Day 1 and Day 2. Conclusion Questions should be answered after the lab is complete. Materials: package of plastic 8 oz drinking glasses or cups 1 liter bottle of club soda or seltzer water masking tape clock or watch 3 fragments of each of the following rock samples: limestone, marble, granite, and sandstone

3 1 copper penny 1 steel nail 1 piece of quartz Procedure: Day 1 1. Fill four cups or glasses three-fourths full of carbonated water (club soda or seltzer water) 2. Fill four cups or glasses three fourths full of tap water. 3. Place masking tape on the cups and label them: limestone and carbonated water limestone and tap water marble and carbonated water marble and tap water granite and carbonated water granite and tap water sandstone and carbonated water sandstone and tap water 4. Place the appropriate rock sample fragments into each labeled cup. Set aside a fragment of each type of rock for a control. These jars will sit for 3 or more days. 5. Perform the Mohs Hardness Test (instructions below) on the control samples that you set aside and record your results on the chart below. Procedure: Day 2 (3 or more days later ) 1. Remove the rocks from the jars and perform the Mohs Hardness Test on each, including your control fragments. Record your results on the chart below.

4 Mohs Hardness Test Procedure: 1. Put each mineral sample on top of its name on the chart. 2. Starting with the first mineral, test how hard it is by trying to scratch it. First try to scratch it with your fingernail, then the copper, then the nail, then the quartz. Be careful! Sometimes something that s much softer than something else will leave a line of powder that looks a lot like a scratch. If you think you have a scratch, rub at it with your thumb. If it s just powder, it ll rub off, but if it s really a scratch, it ll still be there. 3. If you can scratch the mineral with your fingernail, put an X in the Fingernail column. If not, leave it blank and go on to the next column. If you can scratch the mineral with copper, put an X in that column. Keep going until you have tried to scratch the sample with all of your hardness testers. If nothing makes a scratch, leave all of the columns blank. 4. Your testing materials will leave a scratch if they are the same hardness as or harder than the sample. If you get a scratch, the hardness of the mineral is probably somewhere between the hardness of that testing material and the one before it. So, for example, if the quartz and the nail leave scratches on a sample but the penny doesn t, the hardness of the sample is most likely somewhere between copper, hardness 3, and steel, hardness 5.5. So split the difference and call it a 4 on Mohs Hardness Scale. Write this number down in the Hardness column. 5. If not even the quartz will make a scratch, your sample is harder than quartz (7), so write >7 in the Hardness column. If all of the tests produce a scratch, your sample is softer than fingernails (2.5), so write <2.5 in the Hardness column.

5 6. Repeat this procedure for all of your samples. 7. When you re done, list the rock samples in order of hardness, from softest (lowest number) to hardest (highest number). You now have a relative hardness scale of your samples. MINERAL Fingernail (2.5) Copper (3) Steel (5.5.) Quartz (7) Hardness Limestone Marble Granite Sandstone Day 1 ROCK NAME HARDNESS hardest - - softest

6 Day 2 (3 or more days later) MINERAL Fingernail (2.5) Copper (3) Steel (5.5.) Quartz (7) Hardness Limestone Marble Granite Sandstone ROCK NAME HARDNESS hardest - - Conclusion Questions softest 1. Were the fragments that had been immersed in tap water softer than the control samples you tested on the first day of the lab?

7 2. Were the fragments that had been immersed in carbonated water softer than the samples that were immersed in tap water? Were they softer than the control samples? 3. How do you think this experiment is like chemical weathering in nature? 4. How is it different?

8 Chemical Weathering Lab Answer Key Conclusion Questions 1. Were the fragments that had been immersed in tap water softer than the control samples you tested on the first day of the lab? Samples may be slightly softer than the control samples. 2. Were the fragments that had been immersed in carbonated water softer than the samples that were immersed in tap water? Were they softer than the control samples? Yes, they were softer than the control samples and the tap water samples. 3. How do you think this experiment is like chemical weathering in nature? The water that weathers the rocks is not pure water. Chemical weathering changes what a rock is made of. 4. How is it different? In nature it takes more time. Water is usually moving, not soaking a rock on all sides at all times.