  The next generation of space and ground-based solar missions aim to study the
magnetic properties of the solar chromosphere using the infrared Ca II lines
and the He I 10830 {\AA} line. The former seem to be the best candidates to
study the stratification of magnetic fields in the solar chromosphere and their
relation to the other thermodynamical properties underlying the chromospheric
plasma. The purpose of this work is to provide a detailed analysis of the
diagnostic capabilities of the Ca II 8542 {\AA} line, anticipating forthcoming
observational facilities. We study the sensitivity of the Ca II 8542 {\AA} line
to perturbations applied to the physical parameters of reference semi-empirical
1D model atmospheres using response functions and we make use of 3D MHD
simulations to examine the expected polarization signals for moderate magnetic
field strengths. Our results indicate that the Ca II 8542 {\AA} line is mostly
sensitive to the layers enclosed between $\log$ $\tau=[0,-5.5]$, under the
physical conditions that are present in our model atmospheres. In addition, the
simulated magnetic flux tube generates strong longitudinal signals in its
centre and moderate transversal signals, due to the vertical expansion of
magnetic field lines, in its edge. Thus, observing the Ca II 8542 {\AA} line we
will be able to infer the 3D geometry of moderate magnetic field regions.
