Conclusion
The hypothesis for the experiment was; if limestone is chemically and mechanically weathered, than the limestone will weather faster than granite, sandstone, and shale because the limestone is more susceptible to weathering than the other rocks. Based on the results during the two week period, the experiment supports the hypothesis that limestone will weather chemically and mechanically faster than granite, sandstone, and shale.
Supporting results include that all 14 days the ph level of the lemon juice with the limestone changed and the lemon juice’s pH of all the other rocks stayed the same. For the mechanical weathering part, the limestone was changed the most out of the four rocks by the sandpaper and some pieces also fell off from the hammering and dropping. A larger piece fell off the granite from the hammering, but no change was seen by the sandpaper or dropping. Small amounts of weathering was seen on the sandstone and shale from the sandpaper, but little to none from the hammering and dropping.
Students could expand this experiment by using other rocks; such as basalt, gypsum, coal, obsidian, pumice, and rhyolite against limestone to observe if limestone still weathers faster than the others. This way there would be a larger variety of rocks to compare the limestone with.
Based on the data, limestone would not be a good material to build on, because it weathered the quickest in both the chemical and mechanical experiments. The experiment was only for a two week period and weathered greatly with just lemon juice. Imagine if a house was being built on top of limestone, the limestone would slowly deteriorate causing the house to sink.
Also, the background paper mentioned how karst topography, such as sinkholes, can be formed on limestone bedrock when there is chemical weathering present. The data shows how this can happen, because the limestone was weathered the most by the lemon juice.
Data Gaps
During the experiment the jar with the limestone filled up to the top with lemon juice. The jar had to be emptied some so there was room left to add more lemon juice for future days when the pH level changed. The jars could have been larger to hold all of the juice without having to dump some out. Dumping out the lemon juice may have altered the results slightly. In table 1 and graph 1 the pH of limestone shot up and went to 4, unlike the other days with a pH of 3. This changed my results because I had to add more lemon juice to maintain the pH level of 3.
Also all of the rocks except granite came from the same place. The granite was from a sample of a counter top slab, therefore one of the sides was smoothed down already. This may have caused the results from both the chemical and mechanical experiments to change .
During the mechanical weathering part of the experiment, the granite rock was a little smaller than the other types and a piece broke off on the first day, so this could have been because of the size difference. The pieces that broke off the rocks were hit, dropped, and sanded along with the original piece of the rock and it was noticed that they broke again into other pieces very easily, so this also contributes to the size possibility. If the experiment was done again, the rocks would have been closer in size.
Also, one of the experimenters had to do the mechanical weathering in two different locations, so the setting and ground hardness could have affected and changed the weathering of the rocks.
The Effect of Chemical and Mechanical Weathering on Rocks 