Physical changes that involve liquids and aqueous solutions can be studied using a polystyrene calorimeter like the one shown in Figure 1. Such materials can be applied to practical thermochemical systems. For example, when athletes are injured, they may immediately hold an ‘instant cold pack’ against the injury; and over time, the athlete may apply ‘instant hot pack’ to help recover. The medical hot/cold pack operates on the principle that certain salts dissolve endothermically in water, while others dissolve exothermically. The amount of heat per unit mass involved in the dissolving of a compound is a characteristic property of that substance. It is called the enthalpy of solution. The purpose of this experiment is to use calorimetry to determine the enthalpy of solution of an unknown salt, and then to use that value to identify the salt in a medical hot/cold pack, from a list of possible candidates.
This demonstration is an entertaining way to introduce simple chemical reactions and the types of evidence that indicate the occurrence of chemical change, including the production of a gas. A link... read more
Categories: Lab/Student Activity
This activity uses the EdPuzzle platform to assess students understanding of the cell cycle. The students will watch a video through EdPuzzle that has a series of questions embedded in it. They will... read more