Experiment C20: Endothermic and Exothermic Reactions
(Temperature Sensor)

Concept: reactions & energy

Time: 30 m

SW Interface: 300, 500 & 700

Macintosh® file: C20 Endo-Exo Reactions

Windows® file: C20_ENDO.SWS

Adapted by Terri Case, J.I. Case High School, Racine, WI, from Chemistry with Computers, by Dan D. Holmquist and Donald L. Volz, distributed by Vernier Software, 8565 S.W. Beaverton-Hillsdale Hwy., Portland, OR 97225-2429, (503) 297-5317.

EQUIPMENT NEEDED

ï Science Workshop™ Interface

ï temperature sensor

ï balance (to measure mass)

ï beaker, 250 mL

ï graduated cylinder, 50 mL

ï apron and safety goggles

 Chemicals and Consumables ï baking soda (NaHCO3)

ï citric acid (H3C6H5O7), 1.5 Molar

ï hydrochloric acid (HCl), 0.5 Molar

ï magnesium ribbon (Mg)

ï Styrofoam cup

ï weighing paper

 PURPOSE

The purpose of this laboratory activity is to study the energy released during certain types of chemical reactions.

THEORY

Many chemical reactions give off energy. Chemical reactions that release energy are called exothermic reactions. Some chemical reactions absorb energy and are called endothermic reactions. You will study one exothermic and one endothermic reaction in this experiment.

First, you will study the reaction between citric acid solution and baking soda. An equation for the reaction is:

H3C6H5O7(aq) + 3 NaHCO3(s) ---> 3 CO2(g) + 3 H2O(l) + Na3C6H5O7(aq)

Next, you will study the reaction between magnesium metal and hydrochloric acid. An equation for this reaction is:

Mg(s) + 2 HCl(aq)---> H2(g) + Mg Cl2 (aq)

SAFETY PROCEDURES

1. Wear an apron and safety goggles while handling or working near chemicals.

2. Follow your teacherís directions for the handling and disposal of all chemicals and solutions.

 PROCEDURE

For this activity, the temperature sensor measures the temperature of different solutions during chemical reactions. The Science Workshop program records and displays the data.

PART I: Computer Setup

1. Connect the Science Workshop interface to the computer, turn on the interface, and turn on the computer.

2. Connect the DIN plug of the temperature sensor to Analog Channel A on the interface.

3. Open the Science Workshop file titled as shown;

 Macintosh: C20 Endo-Exo Reactions

Windows: C20_ENDO.SWS

ï The document has a Graph display with a plot of the Temperature (C) versus Time (sec).

ï Note: For quick reference, see the Experiment Notes window. To bring a display to the top, click on its window or select the name of the display from the list at the end of the Display menu. Change the Experiment Setup window by clicking on the "Zoom" box or the Restore button in the upper right hand corner of that window.

4. The "Sampling OptionsÖ" for this experiment are as follows: Periodic Samples = Slow at 1 measurement per second and Stop Condition is Time = 250 seconds.

5. The vertical axis on the Graph (Temperature) is scaled from -10 Celsius (C) to 40 C. The horizontal axis on the Graph (Time) is scaled from 0 to 250 seconds.

 PART II: Sensor Calibration and Equipment Setup ï You do not need to calibrate the temperature sensor. The temperature sensor produces a voltage that is proportional to temperature (10mV = 1.0 Celsius). The default calibration is 110.000 C = 1.100 V and -10.000 C = -0.100 V.

1. Place a Styrofoam cup into the 250 mL beaker as shown in the diagram. Put 30 mL of 1.5 Molar citric acid into the cup. Place the temperature sensor into the citric acid solution.

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2. Weigh out 10.0 g of solid baking soda on a piece of weighing paper.

 PART IIIA: Data Recording - Reacting Citric Acid and Baking Soda ï Get ready to record data. The temperature sensor must be in the citric acid solution for a few seconds before you begin recording data.

1. When everything is ready, click on the "REC" button to begin data recording.

2. After about 20 seconds have elapsed, add the baking soda to the citric acid solution.

3. Gently stir the solution with the temperature sensor to ensure good mixing.

4. Record data until a minimum temperature has been reached and temperature readings begin to increase.

5. Click on the "STOP" button to end data recording or let the computer automatically end it after 250 seconds.

ï "Run #1" will appear in the Data list in the Experiment Setup window.

6. Dispose of the reaction products as directed by your teacher. Rinse the cup.

 PART IIIB: Data Recording - Reacting Magnesium and Hydrochloric Acid 1. Measure out 30 mL of HCl solution into the Styrofoam cup. Place the temperature sensor into the HCl solution.

2. Obtain a 20.0 cm piece of shiny magnesium metal from the teacher.

3. Get ready to record data. Note: The temperature sensor must be in the HCl solution for a few seconds before you begin recording data.

4. When everything is ready, click on the "REC" button to begin data recording.

5. After about 20 seconds have elapsed, add the magnesium ribbon to the acid solution.

6. Gently stir the solution with the temperature sensor to ensure good mixing.

7. Record data until a maximum temperature has been reached and temperature readings begin to decrease.

8. Click on the "STOP" button to end data recording or let the computer automatically end it after 250 seconds.

ï "Run #2" will appear in the Data list in the Experiment Setup window.

9. Dispose of the reaction products as directed by your teacher. Rinse the cup.

 ANALYZING THE DATA 1. Click on the Table display to make it active. Save your data by selecting "Save AsÖ" from the File menu.

2. The Table has two columns. Both show Run #2. Use the DATA menu button in the first column to select "Run #1".

3. Click the Statistics button in the left hand area of the Table display.

4. In the Statistics area that opens at the bottom of the Table, find the minimum and maximum values for temperature for Run #1. Record these values in the Data Table.

5. Find the minimum and maximum values for temperature for Run #2. Record these values in the Data Table.

6. Calculate the temperature change for each reaction by subtracting the initial temperature from the final temperature.

 DATA TABLE
Ý Run #1 Run #2
Final temperature (C) Ý Ý
Initial temperature (C) Ý Ý
Temperature change (C) Ý Ý
QUESTIONS
1. Which reaction had a negative ÆT value? Is the reaction endothermic or exothermic? Explain.

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2. For each reaction, describe three ways you could tell a chemical reaction was taking place.

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    1. Which reaction took place at a greater rate? Explain your answer.