In the procedure described, what is used to contain the reaction mixture?

The choice of a polystyrene cup to contain the reaction mixture is suitable because polystyrene is an effective insulator, which can minimize heat loss during exothermic reactions. This is particularly important in a chemistry setting where temperature changes can significantly impact reaction rates and outcomes. The lightweight nature of polystyrene cups also makes them easy to handle and less likely to break compared to glass or ceramic options, ensuring greater safety during experiments.

Additionally, polystyrene cups are generally inexpensive and disposable, making them practical for classroom use where multiple experiments may be conducted. They can hold liquids sufficiently for various chemical reactions while providing convenience without the risk of reactions with the materials being tested, as might occur with some plastic containers. The use of glass beakers or ceramic bowls could be valid in different scenarios but may not offer the same insulating properties and convenience, especially for temperature-sensitive reactions.