The teacher Kelvin was to teach two classes (2A & 2B) about Acids and Alkalis.
He first piqued his students' interest by asking them beforehand to go home and think about what substances in their daily lives are acidic or alkaline, and to bring a small sample of a substance that they thought was acidic or alkaline to the next lesson.
That following lesson, Kelvin had students conduct a trigger experiment on using dragonfruit juice as an indicator to test the pH of certain liquids. He first demonstrated how to extract the dragonfruit juice (this involved mashing and filtering the pulpy residue) and how to test the dragonfruit juice indicator in solutions of different pH (i.e., using droppers, observing colour changes). Students proceeded to conduct the experiment in pairs.
In subsequent lessons, Kelvin facilitated students' insightful discussion on KF (Figs. 1 & 2) regarding the experiment, indicators, pH, acidity and alkalinity.