1. Module 1

1.25. Page 3

Module 1: Lesson 5

Module 1—Thinking Energy

Lesson 5 Lab: Molar Enthalpy of Neutralization

 

Background Information

 

The molar enthalpy for many chemical reactions can be determined experimentally, provided you have appropriate equipment. Earlier you constructed a calorimeter using nested polystyrene cups. In this investigation you will use a calorimeter to determine the molar enthalpy change for a neutralization reaction between aqueous sodium hydroxide and sulfuric acid solutions.

 

Purpose

 

To determine the molar heat of a chemical change (reaction), and to compare the experimentally obtained value with a widely accepted value for the ΔnHm for sodium hydroxide.


Experimental Design

 

The heat of reaction will be measured by combining 30.0 mL of 1.0 mol/L H2SO4(aq)  with 50.0 mL of 1.0 mol/L NaOH(aq). The two reactants will be combined in a simple calorimeter made of two polystyrene cups nested together. Assume that the specific heat capacity of both of these substances is equal to that of water, and that each of these solutions has a density identical to water.

 

Retrieve your copy of the Module 1: Lesson 5 Assignment that you saved to your computer earlier in this lesson. You will record data and complete your analysis in your Lesson 5 Assignment.

 

Materials

  • three polystyrene cups
  • two 50-mL graduated cylinders
  • thermometer
  • mol/L H2SO4(aq)
  • mol/L NaOH(aq)

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 5 Lab: Molar Heat of Neutralization.” If you will not be completing the lab youself, remember to record data and observations as you view the presentation.

 

Procedure

 

Step 1: Nest two polystyrene cups.

 

Step 2: Measure 30.0 mL of 1.0 mol/L H2SO4(aq) solution using a 50-mL graduated cylinder and pour it into the calorimeter.

 

Step 3: Using another 50-mL graduated cylinder, measure 50.0 mL of NaOH(aq) solution.

 

Step 4: Record the temperature of each solution to the nearest 0.1°C.

 

Step 5: Pour the NaOH solution into the calorimeter. Use the third cup as a lid. Insert the thermometer into a hole in the lid, and slowly stir the mixture with the thermometer.

 

Step 6: Record the highest temperature obtained to the nearest 0.1°C.

 

Step 7: Pour the reaction mixture down the sink. The reaction mixture contains dilute excess sulfuric acid and acqueous sodium sulfate, and it does not require specific treatment prior to disposal. Rinse the calorimeter and other glassware used. Put all equipment away.

 

Module 1: Lesson 5 Assignment

 

Retrieve your copy of the Module 1: Lesson 5 Assignment that you saved to your computer earlier in this lesson. Complete Part 1—Lab: Molar Heat of Neutralization. You will receive information later in the lesson on when to complete the rest of the Lesson 5 Assignment and on when to submit your work to your teacher.