November, 2002, Chemistry Experiment:

Classic Endothermic Reaction:
Alka-Seltzer® & Water

- Purpose
- Background Information
- Equipment & Supplies
- Software & Probeware Setup
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions

PASPORT Temperature Sensor
(PS-2125)

ScienceWorkshop
Temperature Sensor
(CI-6505B)
Purpose:

Students will measure the temperature change resulting from the endothermic reaction of Alka-Seltzer tablets with water. They will also observe physical evidence of the reaction and determine if the temperature of the water causes a difference in the rate of reaction.

Background Information:

Alka-Seltzer neutralizes the acids in the gastrointestinal system by combining with hydrochloric acid in the stomach. It reduces gastric acidity and thereby reduces the activity of pepsin. Alka-Seltzer contains both citric acid (C6H8O7 -- anhydrous) and sodium bicarbonate (baking soda -- NaHCO3). When you drop a tablet in water, the acid and the baking soda react, producing the famous fizz. You can think of an Alka-Seltzer tablet as compressed baking soda mixed with a little aspirin.

Endothermic reactions absorb heat energy. Because of this, the surroundings lose heat to the reaction and a temperature decrease can be recorded.

Hypothesize: What affect does the temperature of water have on the rate of reaction and temperature change when combined with Alka-Seltzer?

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Equipment and Supplies:

For each lab group:

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Software and Probeware Setup:

  1. Ensure that your USB Link, Xplorer or ScienceWorkshop 500 interface is connected to the computer.

  2. Click on one of the links below to download a pre-configured DataStudio file for this experiment and then open the file.

    PASPORT users: PS Windows (.zip file) or PS Macintosh (.sit file)

    ScienceWorkshop 500 users: SW Windows (.zip file) or SW Macintosh (.sit file)

    When the file is opened, you should see a Graph Display of Temperature vs. Time, as well as a Digits Display of Temperature.

  3. Connect the Temperature Sensor to the Xplorer or USB Link (PASPORT users), or plug the Temperature Sensor into the 500 Interface (ScienceWorkshop 500 users).

    If you are using the ScienceWorkshop 500 Interface, be sure the interface is turned on and the Temperature Sensor is associated correctly in the Experiment Setup window.

  4. Resize and arrange the displays as needed so you can see them all.

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Experimental Procedure

Reaction Preparation:

  1. Pour 100mL of water into each beaker.

  2. Place one of the beakers into a refrigerator for approximately 30 minutes. The other beaker can be left at room temperature.

Data Collection & Recording:

  1. Conduct the first experiment with the beaker of room temperature water. After completing steps 2-6 repeat the same procedure using the beaker of refrigerator-chilled water.

  2. Click the Start button ( ) to begin collecting data.

  3. Drop one Alka-Seltzer tablet into the beaker of water.

  4. Monitor the temperature for several minutes until no further change is observed, then click the Stop (  ) button to end data collection.

  5. Record the starting and ending temperatures in your data table.

  6. Observe the chemical reaction and record any observations in your data table.


Data Analysis:

  1. Examine the Graph Display to view your data, using the Scale to Fit button ( ) in the Graph toolbar to resize the axes as needed.

  2. Use the Smart Tool ( ) to pinpoint the starting and ending temperatures for each reaction. Record this information in your data table below.

  3. Compare the two Temperature runs and observe the differences in temperature extremes and any variations in the rate of reaction.

    4. Sample Data Table:
    ROOM TEMP WATER
    Observations:
    Temperature Data:
    (°C)
    Start of Reaction:    
    End of Reaction:  
        T for reaction: _____

    COLD TEMP WATER
    Observations:
    Temperature Data:
    (°C)
    Start of Reaction:    
    End of Reaction:  
        T for reaction: _____

Conclusions and Extensions:

  1. What happened to the temperature in the first reaction? Is this evidence of a physical change or a chemical change?

  2. What happened to the temperature in the second reaction? Is this evidence of a physical change or a chemical change?

  3. Is there a correlation between the rate of reaction and the water temperature? Why?

  4. What do you think the result would be if hot water is used?