Earth Science
Weathering, Erosion & Soil
Name:
Lab # 17 - TEMPERATURE AND CHEMICAL WEATHERING
Introduction: Whether it’s the granite of a New Hampshire mountain breaking down into sand and
clay or the limestone of Kentucky decomposing to form rich soil, all
chemical weathering processes involve water. What effect does the
temperature of the water have on the rate at which chemical weathering
occurs?
As you know, carbonic acid is a weak acid that forms when carbon
dioxide dissolves naturally in rain, in streams, or in groundwater. A
common chemical weathering process is the reaction between carbonate rocks, such as limestone
and marble, with carbonic acid. In this lab activity, you will observe a model of t his reaction. By
changing the temperature of the water, you can model the effect of the temperature on the rate of the
reaction between carbonate rocks and carbonic acid.
Objectives:
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Materials:
To Model a chemical weathering process
To graph the data from the model and to interpret the graph
To predict what will happen when the model is modified
To compare the observed data with the theoretical data
Each group will need the following materials for the lab;
5 – 250 mL beakers
5 thermometers
5 effervescent antacid tablets
Hot water (40o – 50oC)
Ice water
Graph paper
Procedures:
PART 1
1.
Arrange 5 beakers in a row. Assign each beaker a number from 1 to 5. Place a
thermometer in each beaker. Each beaker should contain about 200 mL of
water. The water temperature in each beaker will need to be adjusted to match
the following temperatures (use ice or hot water as necessary to make
adjustments).
Beaker 1
Beaker 2
Beaker 3
Beaker 4
Beaker 5
0o – 10oC
10o – 20oC
20o – 30oC
30o – 40oC
40o – 50oC
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2.
Begin with Beaker 1. Remove any pieces of ice from the water. Check to be sure that
the water is within the correct temperature range and that the thermometer has stopped
changing. Read the temperature of the water in Beaker 1 to the nearest 0 .5 degree and
record it in DATA TABLE A: Actual Data. Remove the thermometer from the beaker
and set it aside in a safe place.
3.
READ THIS ENTIRE STEP BEFORE CONTINUING! Drop one of the antacid tablets
into beaker 1. Start the stop watch at the instant the tablet enters the water. Stop the
stopwatch when the last piece of the tablet dissolves. NOTE: It is not necessary to wait
for all of the bubbling to stop; wait only for all pieces of the tablet to disappear.
5.
Read the time on the stopwatch and record it to the nearest 1.0 second on DATA
TABLE A.
6.
Repeat steps 3 and 4 for each of the remaining beakers.
7.
Using your data from DATA TABLE A, plot a graph for the 5 trials. Label the X-axis
Temperature (0C) and the Y-axis Time (seconds). Connect the 5 points with a smooth
curve. Label the curve Observed Data.
8.
Answer questions 1 – 6 in the Analysis and Conclusions.
PART 2
1.
Copy ONLY your Beaker 1 data from DATA TABLE A to DATA TABLE B. The
remaining values in Data Table B will need to be calculated.
2.
For the temperature values, add 10 o C to the reading for Beaker 1 and record that as
the temperature for Beaker 2. In the same way, continue to add 10 oC to each
temperature reading for Beakers 3, 4 and 5 and record in the table.
3.
For the time values on DATA TABLE B, divide the time for Beaker 1 in half to obtain the
time for Beaker 2 and so on. When you divide the values, round off each result to the
nearest whole second.
EXAMPLE: Beaker 2 Time = Beaker 1 Time ÷ 2
Beaker 2 Time = 25 Seconds ÷ 2
Beaker 2 Time = 12.5 Seconds
Record 13 seconds for Beaker 2
4.
Using the same graph as before, plot the e values from Data Table B. Connect the
points with a smooth curve. Label the curve Theoretical Data.
5.
Answer question #7 in the Analysis and Conclusions.
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DATA TABLE A: Observed Data
Beaker Number
Temperature (0C)
Time (seconds)
1
2
3
4
5
DATA TABLE B: Theoretical Data
Beaker Number
Temperature (0C)
Time (seconds)
1
2
3
4
5
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ANALYSIS and CONCLUSIONS: Answer using your knowledge of weathering & erosion and
the graph completed in this lab. [1 point each]
1.
In which beaker did the reaction occur most slowly? In which beaker did the reaction
occur most rapidly? State the relationship between temperature and the rate of the
reaction.
2.
Based upon your observations, what do you think the relationship is between the
temperature and the rate of natural chemical weathering?
3.
Look at the temperatures you recorded. Are all of these temperatures likely to occur on
Earth’s surface? Explain.
4.
How would the rate of the reaction have been different if the tablets had been ground
into a powder before they were dropped into the water? Why?
5.
Look at the calculated values in Data Table B. (a) On your graph, is the line for the
theoretical data above, below, or the same as your line for the actual data?
6.
What does this mean about the rate of the reaction you observed compared with the
theoretical rate of reaction?
7. Which factor has the least effect on the weathering of a rock?
A) composition of the rock
B) exposure of the rock to the atmosphere
C) the number of fossils found in the rock
D) climatic conditions
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8. Four quartz samples of equal size and shape were placed in a stream. Which of the four
quartz samples below has most likely been transported farthest in the stream?
9. The diagram below shows an outcrop of different layers of sandstone in a region receiving
heavy rainfall.
Which sandstone layer appears to be the
least resistant to weathering?
(1) A
(2) B
(3) C
(4) D
10. Slightly acidic groundwater seeps through cracks and openings in limestone bedrock
producing caves. State whether the type of weathering that produces these caves is mainly
chemical or physical, and identify one characteristic of limestone that allows this type of
weathering to occur.
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