South African physical sciences teachers’ use of formulae and proportion when answering reaction-based stoichiometry calculation questions

Abstract

Stoichiometry calculation competence tends to be particularly poor in the developing world, even among teachers. Various methods, including the unit factor method, have the potential to be effective in developing such competence. To evaluate the likelihood of such a generic proportion method, which downplays traditional formula usage, succeeding in a particular context, it is necessary first to understand teachers’ existing competence with proportion and the extent to which their calculation success relies on the explicit provision of and substitution into formulae in their written solutions. This quantitative survey study of 171 South African Physical Sciences teachers’ use of formulae and proportion found that most teachers failed to recognise the need to use proportion for some of the four reaction-based stoichiometry calculation questions used. Provision of and substitution into a formula in the written solution was found to be valuable in helping participants who underutilised proportion to obtain process marks, but to be largely irrelevant to obtaining the correct answer. The findings suggest that professional development interventions in similar contexts should focus on proportion within stoichiometry, particularly on recognition of its relevance to reaction-based questions. While a generic proportion method is well suited to this purpose, questions are raised concerning the likelihood that teachers would accept such a method in a context where process marks favour traditional formats of formula provision and substitution and where process mark attainment is highly valued. The findings also point to the need for teacher education to address competencies other than proportion.

The efficacy of instruction in application of mole ratios and submicro- and macro-scopic equivalent forms of the mole within the unit factor method

“…These assertions are unsurprising, given that (1) multiple valid methods exist in Stoichiometry, including the collection of methods referred to here as formula and proportion strategies, (2) which most of the teachers who rejected the unit factor method were competent in at the start of the intervention (see Fig. 3), and which is favoured in South African chemistry marking guidelines at the school level (Stott, 2021); (3) teacher development tends to be a slow process (Luft and Hewson, 2014), and learning a new algorithm can be time-consuming, as discussed in the limitations section below.…”

“…South African physical sciences teachers' difficulties with stoichiometry calculations Mathematics competence, particularly regarding use of proportion, largely determines the extent of challenge experienced in performing stoichiometry calculations (Ralph and Lewis, 2018). It is therefore not surprising that South African physical sciences (SA PS) teachers, who are known to have difficulty with mathematics in general (Taylor, 2019), and proportion in particular (Selvaratnam, 2011), largely fail to obtain the correct answer to basic stoichiometry calculation exercises (Stott, 2021). These teachers' failure to recognise the need to use proportion was found to be a considerable contributor to their limited success with stoichiometry calculations (Stott, 2021).…”

“…South African physical sciences examination marking guidelines (Stott, 2021), increases the likelihood that uptake ended at the end of the workshop. Additional limitations have been discussed within the text above.…”

“…The sample used in this research is a subgroup of the 220 teachers who attended these interventions. It consists of the same teachers as included in Stott (2021) on the basis of their completion of the pretest, biographical survey and provision of written informed consent to the anonymous use of their data, minus the 10 of that sample who did not also answer the posttest. Some characteristics of the sample are given in Table 2 to enable judgement of the likelihood that findings from this study may be generalisable to other contexts.…”

“…It is therefore not surprising that South African physical sciences (SA PS) teachers, who are known to have difficulty with mathematics in general (Taylor, 2019), and proportion in particular (Selvaratnam, 2011), largely fail to obtain the correct answer to basic stoichiometry calculation exercises (Stott, 2021). These teachers' failure to recognise the need to use proportion was found to be a considerable contributor to their limited success with stoichiometry calculations (Stott, 2021). This failure is consistent with Gulacar et al's (2021) finding that not knowing what to do in subproblems within the calculation process is a critical contributor to difficulties experienced during stoichiometry calculations.…”