Experiment 15

Objective

To determine the enthalpy of solution of sodium chloride (NaCl).

Introduction

The enthalpy of solution is the heat change associated with the dissolution of 1 mole or 1 gram of solute in a solvent. For sodium chloride, when 5.85 g (0.1 M) dissolves in water, the enthalpy change can be calculated from the observed temperature difference.

●       Molecular weight of NaCl: 58.5 g/mol

●       Solution concentration: 0.1 M, requiring 5.85 g of NaCl.

Materials

Chemicals

●      Sodium chloride (NaCl)

●      Distilled water

Apparatus

●      250 mL beaker

●      Glass rod

●      Thermometer

●      Stand

●      Balance

Reagents

●      5.85 g NaCl and 87.4 g distilled water in a 250 mL beaker.

Procedure

1.    Weigh 5.85 g of sodium chloride using the balance.

2.    Place the NaCl in a 250 mL beaker.

3.    Suspend a thermometer in the beaker using a stand and record the initial temperature.

4.    Add distilled water to the beaker containing NaCl.

5.    Wait 2–3 minutes for the temperature to stabilize.

6.    Stir the solution with a glass rod to ensure complete dissolution of NaCl.

7.    Record the final temperature of the solution.

Observation

The initial temperature of the solution is 29.5°C, and the final temperature after dissolution is 27.3°C.

Enthalpy of Solution Calculation:

Enthalpy of solution = 0.42 × (29.5−27.3) × 10 kJ / mol = + 13.44 kJ / mol

Questions

1.    What is solution temperature?

2.    What is molarity?

3.    What is the enthalpy of NaCl?

4.    How is enthalpy measured?