The chemical composition of a low-pressure SF6 plasma in a homogeneous magnetic field is studied using a one-dimensional fluid model. This model takes into account the magnetization of electrons and light negative ions F−. The influence of different parameters such as gas pressure, heating power and magnetic field strength is studied within a parameter range of interest for negative ion sources. The scheme of plasma chemical reactions is analysed in order to identify the main reactions responsible for the generation and decay of plasma species. This sensitivity analysis shows that the scheme of reactions can be significantly simplified.