Question

A student prepares a supersaturated solution by dissolving 60.0 g of ammonium chloride, NH4Cl(s), in 100 g of water at 70 °C. She then gradually cools the solution to 50 °C. Finally, she adds a small seed crystal to the solution. Predict how much ammonium chloride crystallizes out of solution, leaving a saturated solution, explain your answer in words.

Answer 1

3g

When the ammonium chloride solution crystallizes, the oppositely charged ions are brought closer together by the crystal structure. Since formation of a crystal lattice lowers potential energy by placing like charges close together, the system releases the excess energy in the crystallization process. Thus a few grams crystallize