EXPERIMENT 5.2

PURPOSE:

To observe endothermic or exothermic reactions and determine which absorb or release the most energy.

MATERIALS:

• Beaker or a clear glass
• Water
• White vinegar
• Baking soda (A fresh box will work best.)
• Salt substitute (Morton Salt Substitute, Nu-Salt, or NoSalt are brands you can find at your grocery store.)
• Epsom salts
• Hydrogen peroxide
• Steel wool
• Quick rising dry yeast (A new packet—check the expiration date—that has been kept refrigerated will work best.)
• Thermometer
• Tablespoon
• Timer
• Eye protection such as goggles or safety glasses
• Optional—Acetone (Some fingernail polish removers contain acetone. You may be able to find it at a drug or grocery store, read the labels for ingredients.)
• Optional—Styrofoam packing peanut

BACKGROUND INFORMATION:

A way to measure heat energy of a reaction is to measure the temperature change with a thermometer. An endothermic reaction will show a decrease in temperature as the reactants absorb energy from the surrounding area. An exothermic reaction will show an increase in temperature as the products give off energy into the surrounding area. In this experiment you will make solutions in which chemical reactions occur and measure the temperature change.

QUESTIONS:

Which reactions will be endothermic? Which reactions will be exothermic? Why?

HYPOTHESES:

Write your prediction of which combinations of reactants from Table 5.6 will be endothermic reactions and which will be exothermic reactions.

PROCEDURE:

1. Table 5.6 has a list of solvents to combine with solid solutes. Starting with the first combination, fill the beaker or glass with ½ cup room temperature liquid.
2. Insert the thermometer in the solvent and record the initial temperature in your data table. Leave the thermometer in the beaker.
3. Add the solid solute and mix. Record your observations.

3-Minute Timer for Temperature Measurement

3:00

Start Timer Reset 🔊

Ready to start 3-minute timing
4. Wait 3 minutes and record the final temperature of the solution. It's important to measure the temperature of each solution at three minutes. Taking the temperature measurements at the same time for each trial allows you to compare the combinations.
5. Discard the solution, rinse and dry the beaker, thermometer, and tablespoon.
6. Repeat steps 1-5 for each of the combinations 2-4 (and combination 6 if you're doing it) in Table 5.6. (If you are doing combination 6, make sure to do it outside or near an open window as the acetone fumes can be strong.) Record your temperatures and observations.
7. For combination 5, place the steel wool pad in the beaker and cover it with vinegar. Let it set for 2 minutes.

2-Minute Timer for Steel Wool Soaking

2:00

Start Timer Reset 🔊

Ready to start 2-minute timing
8. After 2 minutes take the steel wool pad out of the vinegar and squeeze out any excess liquid. Drain the vinegar and dry the beaker.
9. Wrap the steel wool pad securely around the base of the thermometer and place the steel wool wrapped thermometer back into the empty beaker. Cover the beaker with a paper towel. Record the initial temperature as soon as you set them in the beaker. Wait 3 minutes.

3-Minute Timer for Steel Wool Temperature Reading

3:00

Start Timer Reset 🔊

Ready to start 3-minute timing
10. After 3 minutes record the temperature of the steel wool.
11. Clean up and put everything away. Throw away the steel wool and rinse and dry the beaker, tablespoon, and thermometer.
12. For each trial, calculate the change in temperature of the reaction by subtracting the initial temperature from the final temperature. Record this change in your data table. (Note that some of your answers will be negative numbers. That just means the temperature dropped.)
13. Clean up and put everything away.
14. Graph your results. Make a bar graph for each reaction. Temperature change should be the y-axis with 0 at the origin. Since you will have negative temperature changes and positive temperature changes you will have numbers above and below the x-axis. Remember to label each bar with the reactants.

DATA TABLE:

INTERACTIVE SIMULATION:

Watch this video demonstration of the vinegar and baking soda reaction to see an endothermic reaction in action.

CONCLUSIONS:

Were your predictions correct? Which reactions were endothermic and which reactions were exothermic? How were you able to tell? Write a conclusion paragraph explaining your results and graph in terms of exothermic and endothermic reactions. Make connections to the text.

SUBMIT YOUR RESULTS: