Strong as a Rock? The Effects of Extreme Conditions on the Weathering of Rocks
Science Content Link: Weathering and Rocks
Research Question: I wonder if I increase the temperature and other factors of the water, if the rocks (calcium tablets) will weather (dissolve) faster?
Hypothesis: I predict that as I increase the temperature of the water, the amount of acid, the surface area of the tablets, or the amount of agitation, the calcium tablets will dissolve faster.
Manipulated Variable: I will change the temperature of the water, the acidity of the water, the amount of agitation
(stirring) applied, and the surface area of the tablet.
Responding Variable: rate of weathering of the calcium tablet
Controlled Variables: I will control the size of the container, the amount of time the tablet is subjected to the conditions, the size and shape of the tablets, the amount of liquid in the container, tablet is cut into 4 equal pieces, the intensity of agitation, and the temperature and atmosphere of the room.
Materials:
250ml plastic beaker
(10) antacid calcium tablets
Hot water
Thermometer
Knife
Acetic acid
Stirring Sticks
Stopwatch
Paper Towels
Procedure:
1. Fill the beaker with 250ml of cold water.
2. Place one antacid tablet into the water. Start timer. Record temperature of the water.
3. After 6 minutes, record observations and discard water and tablet.
4. Repeat the above steps with hot water and with an acetic acid solution. Record temperature of solution at beginning and end of the 6 minutes.
5. Repeat procedure with a constant stirring motion of 2 stirs per second in hot water and acidic solution.
6. Repeat above variations after cutting a tablet into 4 pieces.
7. Record observations.

Results:
MANIPULATED VARIABLE
Cold Water (Control Group)
Agitation (stirring)
Hot water
Acetic acid solution
Hot water and stirring
Cut up tablet and hot water
Cut up tablet, hot water, stirring
Cut up tablet, 150ml hot water with
100ml acetic acid solution, stirring
TEMPERATURE ( ̊C) RESPONDING VARIABLE (OBSERVATIONS)
10 Tablet had a couple of bubbles but no noticeable change in size. Water in beaker remained clear.
10
72 start, 56 finish
Tablet decreased in size approximately 10%. Water slightly cloudy with dissolved tablet.
Noticeably increased rate of dissolving. 20% dissolved after 6 minutes. Water cloudy.
14
72 start, 59 finish
72 start, 55 finish
72 start, 57 finish
63 start 51 finish
Tablet bubbled much more than in cold water.
Dissolved approximately 10%.
Tablet dissolved completely in 4:10.
Tablet dissolved 80% in 6 min
Tablet dissolved completely in 2:52
Tablet dissolved completely in 2:05
Results Summary: My results showed that the control group trial had the least amount of weathering occurring – it was not a measurable amount. The cold temperature, even with agitation and acid, resulted in only a slight amount of weathering. With the increase of temperature and surface area, the rates of weathering increased significantly. The fastest rate of dissolving was for the trial where the tablet was cut into pieces and stirred into a mixture of hot water and acid, combining all 4 of our manipulative variables.
Conclusion: In this lab, I found that increasing temperature and other conditions did cause the calcium tablet to dissolve faster. This experiment used antacid tablets to simulate the effects of temperature, acidity, agitation, and surface area on the weathering of rocks. I predicted that increasing any of the four variables would result in faster weathering because I had learned that rocks weather faster in hot, moist, acidic environments and when they have greater surface area and agitation. This lab confirmed my hypothesis by showing that increasing each variable increased the rate of weathering. The experiment showed that each variable either increased the amount of the tablet that dissolved or decreased the time required to dissolve it altogether.

Additional Discussion: During this lab, I had a few problems that may have affected my results. The hot water seemed to be a slightly different temperature each time. The tablets were all different colors, and I wonder if that could have affected the rate at which they dissolve. We ran out of acid towards the end, and so my last trial was in only 100ml of acetic acid. We had to go to break in the middle of the stirring in hot water, and our stirring was interrupted. It was hard to estimate the percent of the tablet that had dissolved, and there is likely some error in those estimations. Most of the other students in the class had similar results as we did, showing that weathering occurs faster under these conditions. I suggest that instead of estimating the percent loss of the tablet, that the lab measure the mass of the tablet after 6 minutes to find the actual mass lost. I wonder how we could experiment with ice wedging and abrasion in this lab? Or how different types of acid would cause faster weathering?