  White dwarfs correspond to the final stages of stellar evolution of
solar-type stars. In these objects, production of energy by nuclear burning has
ended which means that a white dwarf simply cools down over the course of the
next billion years. It is now known that white dwarfs spend some of their
cooling history in an instability strip. The pulsating white dwarfs with an
hydrogen atmosphere (called DAV or ZZ Ceti stars) show non-radial oscillation
modes with periods in the range 100 - 1200s. In this work we try to illustrate
how the oscillation p-mode frequencies of idealized white dwarf models change
as the result of a different chemical composition in the core, with the
ultimate goal of determining the chemical stratification from seismic
observations. The presence of acoustic glitches in the internal structure
results in a periodic signal in the frequencies. We find that this signal
depends on the chemical stratification/composition of the core in a form that
can be analytically modelled.
