We have applied photoelectron spectroscopy to investigate the surface composition after different surface treatments involving Br-2-H2O mixtures in order to study wet chemical etching. Emersion experiments from Br-2.H2O solution are compared with model experiments, in which Br-2-H2O adsorbate and coadsorbate mixtures react with clean GaAs(110) surfaces. Our results indicate that Ga- and As-bromides formed initially are hydrolyzed to form the respective oxides. Without addition of Br-2, only slight oxidation of the surface takes place, There is an enrichment of Ga due to loss of As both in adsorption as well as in emersion experiments. Since in emersion experiments only a final situation is analyzed, the relative influence of surface reactivity and subsequent solvation effects cannot be distinguished easily, while model experiments give clear information on reaction products formed intermediately. However, model experiments differ in environment and temperature from the real solid-liquid interface. The presented results demonstrate that a combination of emersion and model experiments provide valuable insight into the mechanism of wet chemical etching on a microscopic level.