Discrepant Events

Discrepant events are occurrences that go against what we would normally think to happen. For example, if we pour water into a cup and then turn the cup upside down, we would normally expect the water to spill out. Therefore, a discrepant event would occur if the water did not pour out, but had instead “disappeared” (or rather absorbed by powder when my college professor performed it for our class).

Discrepant events carry a particular power within the realm of chemistry education. We all enter a chemistry classroom with certain preconceived ideas of what “should” happen or what “should” be true. These “should happens” are often based upon previous experiences that we have had. Therefore, when those previous experiences are challenged by a discrepant event, student interest can be peaked, and a door can be opened for new learning. This can help to begin the process of conceptual change by causing cognitive disequilibrium that encourages us to search for new answers/explanations.

In chemistry, one discrepant event that can be useful when teaching measurements is showing students that 1 cm3 does indeed equal 1 mL. To do so, a square box that has a volume of 1000 cm3 and a graduated cylinder with a volume of 1000 mL are used. The volume of the box can be confirmed by stacking cubes of 1 cm3 in a 10 x 10 x 10 arrangement. Naturally, it looks like the 1000 mL graduated cylinder can hold more water since it appears taller. However, when 1000 mL of water is measured into the graduated cylinder and then poured from the cylinder into the box, it fits exactly. Students smile, and are able to conclude that 1 cm3 does indeed equal 1 mL.

What other discrepant events do you use in your classroom?