Hands-on activities to improve students' Conceptual understanding of water hardness

Brenda Read-Daily, Elizabethtown College


Hardness removal is a topic typically covered in water treatment courses. Students commonly hold misconceptions about what is meant by hard water. This paper explores hands-on activities centered around hard water to improve students' conceptual understanding of what hardness is and its associated problems. As a pre-assessment, students were asked to define hardness in the context of water quality then describe what problems it causes. They were then guided through two short in-class activities designed to illustrate the impacts of hardness. Students washed dirty glass beakers using soft or hard water using equal amounts of liquid soap. They observed the difference in the quantity of suds generated as well as the buildup on the beaker following rinsing and air drying. Later, in a separate activity, they measured hardness using titration kits using different water samples: bottled water, distilled water, tap water, and water softened using a home water softener. Using the hardness scale, they classified the water samples as being soft, moderately hard, hard, or extremely hard. These activities preceded lectures covering the formal definition of hardness, calculation of total hardness, the lime/soda ash water softening process, and ion exchange. Students enjoyed these activities with some showing increased interest by bringing in additional water samples from home or other locations on campus. Pre-assessment results revealed that a majority of the students were confused about the source of hardness with 0% reporting a completely correct definition, 42.8% a partially correct definition, and 57.2% reporting a completely incorrect definition. However, 64.3% knew that it causes buildup on surfaces. Post-assessment conducted via exams revealed that students' conceptual knowledge improved and from midterm to final exam.