Abstrakt
The ability to solve chemical calculation problems is a key prerequisite for a number of chemical disciplines as well as laboratory activities within chemistry teacher education (Srougi & Miller, 2018). However, previous results (Rusek et al., 2021) showed students have not mastered these at upper-secondary schools was proved not to be accurate.
Specific problematic areas were therefore searched for. For this reason, this research aimed at students' ability to solve specific types of chemical calculations and the influence of the assignment type on their performance.
In order to find out what areas need to be addressed in the corresponding university course, a sample of freshmen pre-service chemistry teachers (N = 22) took two tests at the very beginning of the winter semester 2020 and at its end. The research tool (test) included: dilution problems, mass fraction, molar concentration, calculations from chemical equations and calculation of pH.
Two tasks for each calculation type were included in the test: word-problem and a form of values and quantities. The test was assessed by an expert panel (N = 8).
Also, 12 students chosen based on their performance were also interviewed after passing the course. The results showed, the students' initial skills were rather poor.
Only the mass fraction and molar concentration tasks were solved by the majority of the students. Only up to one third solved the pH or chemical equation calculation tasks.
Considering the level of the tasks, this pointed to their unsatisfactory upper-secondary school preparation. The mistakes stemmed mostly from the students' use of a memorized formulae they only tried to substitute numbers in.
Second the most common reason for their failure were numerical errors, in case of logarithm students' inability to convert pH to c. Only in case of the calculations from chemical equations, a significant difference with a small effect-size between the word-problem and values-formulated task was found (p = .02, r = .297).
As far as the post-test - pre-test difference was concerned, students did significantly better on the post-test showing they learned something in the course. Statistically significant difference with a large, resp. medium effect-size was found for all types of calculations except from the already well-solved mass fraction tasks (p < .001, r = .728 for pH, p < .001, r = .728 for dilution problems; p = .006, r = 498 for molar concentration and p = .006, r = .495 for chemistry equations calculations).
In the interviews, the students mentioned learning to "use the formulae" rather than think about the problems. They also expressed their satisfaction with the course on the basis of the teachers' attitude as well as clarifications which help them understand the principles.
The results revealed upper-secondary school chemistry education could be improved in the way chemistry calculations are being taught. Also, the university course's focus on particular calculation types can be changed as students master some of them already and more time needs to be dedicated to more problematic ones.