The hydrodynamics of bubbly flows is dominated by bubble-induced turbulence and bubble-bubble interactions. Both phenomena influence the gas-liquid mass transfer as well as the mixing of reactants. If the time scales of mass transfer and mixing are in the same order as the time scales of a parallel-consecutive reaction, the yield and selectivity will be affected by the local hydrodynamics. An experimental setup is presented that enables the investigation of mass transfer during well-defined and adjustable bubble collisions. The influence of CO2 bubble collisions on mass transfer is measured and modeled with a modified Sherwood number correlation. Further visualization of the concentration field in the vicinity of O-2 bubbles by means of laser-induced fluorescence demonstrates the dependency of mass transfer from a chemical reaction and permits the development of a first model approach.