Module 1

Module 1—Thinking Energy

Module 1: Lesson 7 Lab—Applying Hess’ Law

 

Purpose

 

To use Hess’ law to determine the molar enthalpy of combustion for a reaction that cannot be determined experimentally with available equipment.

 

Problem

 

What is the molar enthalpy of combustion for magnesium?

 

Prediction

 

The accepted value for this reaction is –601.6 kJ/mol of magnesium reacted.

 

Retrieve your copy of the Module 1: Lesson 7 Assignment that you saved to your computer earlier in this lesson. You will record data and complete your analysis in your Lesson 7 Assignment.

 

Materials

• lab apron
• eye protection
• magnesium ribbon
• magnesium oxide powder
• mol/L hydrochloric acid (100.0 mL for each trial)
• three polystyrene cups
• thermometer
• 100-mL graduated cylinder
• scoopula and weighing boat or paper
• steel wool
• electronic balance
• ruler

If you have access to the materials listed, you may be able to perform this investigation.

If you do not have access to these materials and a supervised laboratory, or if you would like to see the lab performed before you attempt it, view the virtual investigation “Lesson 7 Lab: Applying Hess’ Law.” If you will not be completing the lab yourself, remember to record data and observations as you view the presentation.

 

Procedure

 

Part A

 

Step 1: Construct a calorimeter by nesting two polystyrene cups.

Step 2: Measure 100.0 mL of HCl(aq) and pour it into the calorimeter.

Step 3: Record the temperature of the contents of the calorimeter.

Step 4: Use the ruler to measure approximately 15 cm of magnesium ribbon.

Step 5: Use the steel wool to remove the coating from the magnesium ribbon.

Step 6: Measure and record the mass of the magnesium ribbon using the electronic balance.

Step 7: Add the magnesium ribbon to the calorimeter, and gently stir the calorimeter contents using the thermometer.

Step 8: Place the lid on the calorimeter, and record the highest temperature of the calorimeter contents.

Step 9: Empty the calorimeter into the appropriate waste container, and rinse the calorimeter with water.

 

Part B

 

Step 1: Measure 100.0 mL of HCl(aq) and pour it into the calorimeter.

Step 2: Record the temperature of the contents of the calorimeter.

Step 3: Measure and record approximately one gram of magnesium oxide.

Step 4: Add the magnesium oxide to the calorimeter, and gently stir the calorimeter contents using the thermometer.

Step 5: Place the lid on the calorimeter, and record the highest temperature of the calorimeter contents.

Step 6: Empty the calorimeter into the appropriate waste container and rinse the calorimeter with water.

Step 7: Return all materials to their place in the lab.

 

Module 1: Lesson 7 Assignment

 

If you have not already done so, retrieve your copy of the Module 1: Lesson 7 Assignment that you saved to your computer earlier in this lesson. Complete the Assignment and save it in your course folder. Submit a copy of your completed Module 1: Lesson 7 Assignment to your teacher.

 

Make sure you have saved a summary of what you’ve learned in Lesson 7 in your course folder. You will need this summary to complete the Lesson 8 Assignment.

 

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