Item #: PF2051
In this lab experience, students investigate the energy changes that accompany the dissolution of common laboratory salts in water and apply the results to design a hand warmer that is reliable, safe and inexpensive. Based on temperature measurement results, students will determine that dissolution of NaOH and CaCl2 releases heat energy, whereas dissolution of NaCl and NH4Cl absorbs heat from the surroundings. Then they will explain the results, based on differences in the strength of ionic bonds in the solid compounds, intermolecular water forces, and the interactions between ions and water molecules in solution. Finally, students will propose the design of hand warmers using a solution of CaCl2 or NaOH in water and instant cold packs using aqueous NH4Cl.
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