Thermal Transitions in Copper Sulphate Pentahydrate Molecular Rotation and the Dehydration of Hydrates

Abstract

A study of the thermal transitions in copper sulphate pentahydrate has been made from warming curves obtained by a differential thermocouple method. Small transitions were observed at 29°C, 35°C, 53.7°C, and dehydrations at 96.5°C, 102°C, and at 113°C. The first three of these may be interpreted as transitions from oscillation to rotation of the water molecules in the crystal. The last three are associated with the stepwise dehydration to the tetra‐, tri‐, and monohydrates, respectively. The existence of the tetrahydrate, not previously known, has been demonstrated. A discussion of the dehydration in the light of its crystal structure is given. A mechanism of dehydration by heat, based on the concept of molecular rotation, has been suggested.