Mixing, especially on molecular scale, is a key parameter for controlling rapid chemical synthesis in liquid media. Macro, meso and micro mixing influence significantly reaction kinetics and thus the particle formation as well as the resulting product properties. In this study, mixing in a static T-shaped mixer is investigated experimentally and numerically by different approaches. Firstly, particle-image-velocimetry (PIV) and laser-induced-fluorescence (LIF) techniques are applied to characterize mixing at different length and time scales. Thereby all relevant flow structures down to the Batchelor length scale are detected by a special high resolution LIF set-up (HR-LIF). Secondly, nanoparticle precipitation is used to quantify the micro mixing efficiency. These experimental approaches deliver two global parameters, namely the mean size and the width of the particle size distribution (PSD), showing explicitly the effect of mixing efficiency on the chemical reaction and on particle formation. Based on the experimental results a theoretical model is developed, which couples the fluid dynamics with the solid formation kinetics. This model predicts accurately the complete shape of the resulting PSD for the precipitation of barium sulfate in a T-mixer and visualizes the relevant kinetic data in three dimensions in the mixer.