The demixing effect in a wall-stabilized arc leads to sulphur depletion in the central part of the arc where the ratio between fluorine concentration and sulphur concentration becomes higher than six. We have calculated material functions for different real or fictitious gases , with (specific heat, electrical and thermal conductivities, net emission coefficient) and used them in a one-dimensional model based on Patankar's algorithms. The electric field and the temperature radial profile have been calculated versus the current intensity using 5 mm and 3.2 mm arc diameters. Comparison with experimental results in the literature shows that the influence of demixing on the axis temperature is greater than the experimental error. Thus, we conclude that validating material functions of plasma by comparing experimental and theoretical values of temperature in wall-stabilized arcs needs to take into account demixing effects.