Hidden misunderstandings

Chemistry education aims to help students to build conceptual understanding to support competence in problem solving. A key challenge for assessors is to find a way to genuinely test students’ understanding of concepts and their ability to apply this to the problem in hand. It has previously been shown that students are often able to answer questions correctly simply by applying algorithms and rules. Nyachwaya and colleagues have investigated the ways in which college students use such memorised algorithms in tackling questions related to chemical reactions.

The authors previously reported an investigation into students’ understanding of balanced symbol equations at the particulate level by examining drawings made by students to illustrate reactions. This work showed that, while the majority of students correctly balanced a given equation, relatively small numbers could draw appropriate particulate diagrams to illustrate the meaning of the equation.

The current study used interviews (10 students) to probe the reasoning involved in forming answers and drawing the accompanying diagrams. In one example, a student was found to have applied a particularly regimented approach to balancing an equation, which with further questioning was found to be a poorly understood algorithmic method. In another case, a student rationalised the subscript ‘2’ in Ca(NO₃)₂ as being the results of charge transfers from calcium to nitrate, which was attributed to her misinterpretation of the familiar ‘crossover’ diagram commonly taught to support students in working out the formulae of ionic compounds.

Where students had drawn diagrams that correctly illustrated the different sizes of atoms, the interviews uncovered flawed logic. In an illustrative example, a student had correctly shown a water molecule to be v-shaped with a larger central oxygen atom, but stated that she ‘just drew it as a Mickey Mouse’ without understanding why. Where there was a requirement to illustrate what happens when ionic compounds dissolve in water, students often started with a covalent representation before applying the concept of the compound ‘breaking apart’ into ions.

These findings shed light on the specific algorithmic methods applied by students in these contexts and highlight the difficulties in setting appropriate written assessments to judge chemical competence. The authors also note the challenge faced by instructors in teaching students who have previously ‘succeeded’ by applying algorithms and rote-learning, which may have been encouraged by their previous teachers. The authors suggest that a good approach is to expose students to situations where a particular algorithm doesn’t work and to discuss the conditional thinking one should apply in selecting the appropriate strategy required to solve a problem.