ALKA SELTZER LAB: HOW DOES TEMPERATURE AFFECT RATE OF CHEMICAL WEATHERING?
NAME ______________________________
DATE ____________
In this investigation, you will observe a model of a weathering reaction. You will also observe the affect of temperature
(in this case, water temperature) on the rate at which the reaction occurs.
HYPOTHESIS: How will water temperature affect the rate at which an antacid tablet dissolves in water? Explain your
reasoning. ______________________________________________________________________________________
_______________________________________________________________________________________________
MATERIALS: graduated cylinder, plastic beaker, 250 mL beaker, thermometer, antacid tablet, water in the specified
temperature range, electronic balance, graph paper, timer
PROCEDURE
1. Each team will be assigned a water temperature range. Circle the range assigned to your team: 0 – 10oC
10 – 15°C 15 – 20oC 20 – 25°C 25 – 30oC 30 – 35°C 35 – 40oC 40 – 45 °C 45 – 50oC 50 – 55°C 55 – 60oC
2. Measure the mass of an antacid tablet. Record it on the Data Table.
3. Use hot water, cold water, ice, etc. as necessary to adjust the temperature of a water sample to within the range
assigned to your team. Aim for a temperature near the middle of the range. Mix and measure water in the large
plastic beaker. When you achieve the proper temperature, be sure it is a stable temperature. (Leave the
thermometer in the sample for a minute or two and be sure the temperature does not continue to rise or fall.)
Measure the temperature to the nearest half-degree. Record it on the Data Table. Use the graduated cylinder to
measure 200 mL of water and pour it into the 250 mL beaker.
4. READ THIS STEP BEFORE DOING ANYTHING!!!
You will measure the time it takes for the antacid tablet to dissolve in the water sample. Start timing as soon as the
tablet hits the water. DO NOT STIR! Stop timing as soon as the tablet is completely dissolved. DO NOT WAIT
for all the bubbles to disappear, just until the tablet is gone. (It may be helpful to observe through the bottom of the
beaker.) Record the time to the nearest second on the Data Table.
5. Empty and rinse the beaker. Clean up the lab area.
6. Calculate the rate of reaction by dividing MASS of tablet (in grams) by TIME (in seconds) that it took the tablet to
dissolve. Record the answer on the Data Table.
7. Record your team’s data on the Class Data Table at the front of the room. BE SURE TO RECORD THE DATA IN
THE CORRECT COLUMN ON THE TABLE!
8. Copy the results for all the other groups in the class. There will be more than one set of data for some temperature
ranges. COPY ALL DATA.
9. Prepare a graph of Temperature versus Time. Plot temperature on the y-axis beginning with 0oC. Plot time on the
x-axis beginning with 0 seconds. Plot ALL points and draw a smooth BEST-FIT CURVE.
DATA TABLE
0-10oC
A
B
Mass of tablet
(grams)
Water temperature
(oC)
Time to dissolve
(seconds)
Rate of reaction
(grams/second)
10-20 oC
A
B
20-30 oC
A
B
30-40 oC
A
B
40-50 oC
A
B
50-60 oC
A
B
QUESTIONS – Answer in complete sentences. USE YOUR TEXT, CHAPTER 14, AS A REFERENCE.
1.
Examine your graph and data table. DESCRIBE your graph. Then explain what it illustrates about the general
relationship between temperature and rate of reaction. Is there a direct correlation between the two? Were the
results of the experiment consistent with your prediction?
2.
Were there any data points that did not fit well on the curve?
Describe some SOURCES OF
ERROR that could influence the accuracy of results obtained by different groups. Consider all the steps in the
procedure. Give more than one reason for errors.
How could the experiment and/or data collection be improved to obtain better data?
3.
This experiment modeled a
(mechanical or chemical?) weathering process.
4.
How could you increase the rate of reaction in the coldest water without changing the water temperature? (Hint:
read the section called “Amount of Exposure” in the weathering chapter of the text.) Explain WHY it would make
the reaction faster.
5.
Climate plays an important role in determining natural rates of weathering. Based on the results of the lab, what
can you infer about the relationship in nature between temperature and weathering rates? Would you expect
chemical weathering rates to be faster in a warm or cold climate? What other climate factor(s) influence rates?
6.
All of the temperature ranges tested in this lab occur somewhere on Earth’s surface. Suggest some specific
geographic locations where the warmest and the coldest temperature ranges might occur.
7.
Seattle, Washington is located at 43oN latitude. Rio de Janeiro, Brazil is located at 23oS latitude. Both locations
have SIMILAR humidity. Both have limestone (composed of calcite) bedrock near the surface. What chemical
weathering process specifically affects limestone?
At which location, Seattle or Rio de Janeiro, will limestone weather more rapidly? EXPLAIN WHY.
8.
Barrow, Alaska (70°N) also has limestone bedrock. Explain why limestone weathers very slowly in Alaska. Use
evidence from the lab to support your answer.
9.
Examine the pictures of Cleopatra’s Needle in the textbook (or look it up on-line). Why did the carvings on the
granite obelisk weather rapidly when moved from Egypt to New York? What mechanical and chemical
weathering processes were involved?
0 – 10°C
A
10 – 20°C
A
20 - 30°C
A
0 – 10°C
A
10 – 20°C
A
20 - 30°C
A
0 – 10°C
B
10 – 20°C
B
20 - 30°C
B
0 – 10°C
B
10 – 20°C
B
20 - 30°C
B
0 – 10°C
A
10 – 20°C
A
20 - 30°C
A
30 – 40°C
A
40 – 50°C
A
50 – 60°C
A
30 – 40°C
A
40 – 50°C
A
50 – 60°C
A
30 – 40°C
B
40 – 50°C
B
50 – 60°C
B
30 – 40°C
B
40 – 50°C
B
50 – 60°C
B
B
A
A
B
10 – 20°C
0 – 10°C
B
A
A
B
10 – 20°C
0 – 10°C
B
A
B
20 – 30°C
A
20 – 30°C
B
A
B
30 – 40°C
A
30 – 40°C
B
A
B
40 – 50°C
A
40 – 50°C
B
A
B
50 – 60°C
A
50 – 60°C
Rate of
reaction
(g/sec)
Time to
dissolve (sec)
Water temp.
(°C)
Mass of
tablet (g)
Rate of
reaction
(g/sec)
Time to
dissolve (sec)
Water temp.
(°C)
Mass of
tablet (g)