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We analyse various parameters of chemical models that may severely
affect our attempts to interpret molecular line observations of prestellar
cores. We use the CB17 prestellar core as an example of an isolated
prestellar core for which detailed spectral maps are available. It is
demonstrated that, even when extensive observational datasets are present,
their analysis is not straightforward, as some unknown factors can mimic
other unknown factors. For example, the attempt to estimate the core age
based on the central molecular depletion can be hampered by the unknown
value of the effective sticking probability. Also, in some cases minor
variations in the cosmic ray ionisation rate and the inclusion of surface
chemistry in the model can act in the opposite directions. These and other
ambiguities are discussed in the contribution. Some ways to relax the
degeneracy of modelling results are also presented.
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