The carbon dioxide problem

Chemistry educators worldwide advocate inquiry-based practical work in the secondary school chemistry curriculum. However, good contextualised scientific inquiries for chemistry students are scarce.¹ Here I describe an inquiry-based experiment done by Secondary 4 chemistry students (aged 14-15 years) in Hong Kong. This investigation can provide students with an excellent opportunity to understand part of the global carbon cycle.^2,3

The carbon dioxide problem 

The purpose of this investigation is not for students to arrive at a single, 'correct' answer but to develop inquiry skills. Box 1 illustrates the problem. Students are seldom aware that bacteria and fungi feed on the dead remains of plants and, via respiration, release CO₂ to the atmosphere. Leaf litter decomposition is a key process in the global carbon cycle. Each year, the mass of CO₂ released by decomposing leaves is approximately equal to that released by animal and plant respiration. 

In a trial of the experiment, working with teachers, we divided a class into groups of three-four students based on their abilities. After about 30 minutes, we collected their plans for evaluation. The next day, we invited the students to present their plans to the rest of the class. This is done to turn assessment activities into a teaching-learning activity. Twenty minutes were allocated for each presentation. Each group needed to answer questions raised by other students. After the presentations, students did experiments according to their plans. The problem has been designed to be an open-ended investigation so students should be allowed to try out their own plans.