Molar Enthalpy of Solution

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The purpose of this investigation is to practice the scientific and technological skills associated with calorimetry. Before you do the investigation, decide how precise each measurement should be to provide maximum certainty for your experimental result.

Problem

What is the molar enthalpy of solution of an ionic compound?

Experimental Design

Once an ionic compound is chosen, the approximate mass of the compound required to make 100 mL of a 1.00 mol/L solution is calculated and then is measured precisely. Use the MSDS to determine the hazards associated with the compound and take the necessary precautions. The temperature change is measured as the compound dissolves in the water in a calorimeter.

Procedure

1. Set the water value at 100 mL.
2. Choose NaCl from the compound menu.
3. Set the mass of the compound chosen to 5g.
4. Record the initial temperature of the water in the chart provided.
5. Click the Start button to add the compound to the water.
6. Record the final temperature of the water in the chart provided.
7. Repeat the process for all the ionic compounds.

 

 


Chemical Education Research Group, Iowa State University, Ames IA

Observations

Compound Initial Temperature (C) Final Temperature (C)
NaCl    
     
     
     
     
     
     
     
     
     
     
     

Analysis

1. Calculate the change in temperature for each ionic compound.

2. List three assumptions made in student investigations involving simple calorimeters.

3. In a calorimetry experiment such as this, which measurements limit the certainty of the experimental result?

4. In a chemistry experiment, 10g of urea ((NH2)2CO) is dissolved in 150mL of water in a simple calorimeter. A temperature decrease of 3.7C is measured. Calculate the molar enthalpy of solution for urea.

5. List the compounds in order from the most exothermic to least exothermic.