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?
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 this 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
- 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.
Materials
3 -250 mL beakers
thermometer
3 - effervescent antacid tablets
hot water (40 - 50 degrees C)
warm water (20 – 30 degrees C)
ice water (0 - 10 degrees C)
stopwatch
map of Earth's Climates (Classroom Atlas Book)
Procedure
- Arrange 3 beakers in a row. Assign each beaker a number from 1 to 3. Each beaker should contain about 200--mL of water. The water temperature in each beaker will need to be adjusted to match the following: Beaker 1, hot water (40 - 50 degrees C), Beaker 2, warm water (20 – 30 degrees C), and Beaker 3, ice water (0 - 10 degrees C).
- Begin with Beaker 3. 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 3 to the nearest half degree and record it on Data Table A. Remove the thermometer from the beaker and set it aside in a safe place.
- Read this whole step twice before beginning the step. (Continued on next page)
- Drop the antacid tablet into Beaker 3. Start timing (seconds) at the instant the tablet enters the water. Stop the timing when the last piece of the tablet dissolves. (You do not need towait for all of the bubbling to stop; wait only for all pieces of the tablet to disappear.)
- Record the time to the nearest whole second on Data Table A.
- Repeat the steps 2 and 3 for each of the remaining 2 beakers using the correct temperature ranges.
- Copy the temperature results you have for Beaker 1 from Data Table A to Data Table B. The remaining values in Data Table B will need to be calculated. For the temperature values; add 10 to the reading for Beaker 1 and record that as the temperature for Beaker 2. In the same way, add 10 to the beaker 2 temperature and record that as the Beaker 3 temperature.
- Copy the time results you have for Beaker 1 from Data Table A to Data Table B. The remaining values in Data Table B will need to be calculated.For the time values;the time for Beaker 2 will be one half of the time for Beaker 1 and the time for Beaker 3 will be one half of the time for Beaker 2. When you divide the values, round off each result to the nearest whole second.
- Plot a graph of the data. Make sure you know what the independent (y-axis) variable is and what the dependent (x-axis) variable is. “Which variable is dependent on the other one?”
**** You’ll need to work on the Climate Information with the Atlas’ in class and save the graphing part for after you’ve completed the Atlas work!
Name: ______Date: ______Class: ______
OBSERVED DATA (Data Table A)
(Observed = what you actually see happening)
Beaker Number / Temperature (ºC) / Time (s)1-A
2-A
3-A
THEORETICAL DATA (Data Table B)
(Theoretical = what you might see happening in an actual experiment)
Beaker Number / Temperature (ºC) / Time (s)1-B / 1A temp = / 1A time =
2-B / 10 + 1-A temp = / ½ 1-A time =
3-B / 10 + 2-B temp = / ½ 2-B time =
Graph both your Observed and Theoretical Data. Be sure to put the correct variables in the correct places on your graph. You know, Dependent and Independent Variables!!! Which variable depends on the other? Use different colors to show Observed and Theoretical.
Analysis and Conclusions
1.
a)In which beaker did the reaction occur most slowly? ______
b)In which beaker did the reaction occur most rapidly? ______
c)What do you think is the relationship between the temperature and the rate of a reaction in the experiment?
- Based upon your observations, what do you think is the relationship between the climate and the rate of natural chemical weathering?
- Turn to the map of climates on pages 36 and 60 in Classroom Atlas provided. Locate Rio de Janeiro in South America and Seattle in North America. The map key indicates that both cities have climates with abundant moisture.
a)Recall what you know about carbonic acid in rain and in groundwater. Compare the weathering rate of a limestone in Rio de Janeiro with that of a limestone in Seattle. Is there a difference? Explain your answer.
- Now locate Barrow, Alaska, use the map on page 34 in the Atlas to see where Barrow is! Then turn the page (pg 36) to determine the climate in Barrow.
b)Why is a limestone in Barrow likely to weather very slowly
- 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?