Presenters' pedagogical choices are strongly affected by whether they view knowledge as coherent or fragmented. This mixed-methods survey study seeks to contribute to epistemological discussions and associated pedagogical suggestions in the context of mole ratio related mistakes evident in stoichiometry calculations performed by in-service teachers in a developing world country. Physical sciences teachers in South Africa were asked to solve four stoichiometry calculation questions, and their written solutions (361 sets) were analyzed for consistency of various types of mole ratio related mistakes. The study found high levels of inconsistencies in each observed mistake, supporting the view that most participants' knowledge lay closer to the fragmented end of the coherent-fragmented epistemological continuum. Evidence is presented for differential cognitive load, overgeneralization, and intuitive heuristics as possible explanations for these mistakes. Pedagogical suggestions are made for addressing such errors in in-service chemistry teacher workshops about stoichiometry calculations, although these may only be applicable where teacher subject matter knowledge tends to be low, such as within the developing world.