The crystallographic properties of a commercial potassium acetate powder have been analysed before and after various heat treatments. From X-ray diffraction patterns and scanning electron microscopy it is shown that the initial material is constituted by two chemical compounds which are characterized by tetragonal structures. After heating either by means of a microwave monomode, or under a poor vacuum at low temperature (363 and 413 K), one of these compounds disappears. This one is very likely a hydrated form of the acetate. Additionally, infrared and Raman spectra of the potassium acetate have been recorded. The absorption bands have been compared to those of sodium acetate. Moreover, X-ray absorption spectra (recording of the K edge of potassium) corroborates the desorption of water from the powder maintained under high vacuum.