Why does Basic Copper Sulphate Change its Color?


Any change in color of a substance tells us about chang […]

Any change in color of a substance tells us about changes happening in its structure since the latter is responsible for the color itself. As clearly seen from an initial Basic Copper Sulphate formula CuSO4*5H2O, this blue crystal compound, besides copper sulfate, also contains water. Such solid substances comprising water in their composition are often called hydrates.

Water is bound to copper sulfate in a specific way. When hydrate is heated, water is being removed from it, just as boiling water from a kettle. Obviously, this process breaks bonds between water molecules and copper sulfate, causing the compound change in color.

A Molecule of water is polar, i.e. charges are unevenly distributed within it. What does it mean? Simply put, it means that there is an excess of positive charge on the one end of a molecule and an excess of negative charge – on the other end. When they are summed up, the resulting charge is zero, as molecules are not normally charged. Still, certain parts of such molecules may carry a positive or a negative charge.

Oxygen atoms attract negatively charged electrons much stronger than hydrogen atoms do. As a result, a negative charge in a water molecule is focused on oxygen, while a positive charge – on hydrogen atoms. Combined with the certain geometry of a molecule, this uneven charge distribution makes water molecules dipole (from the Greek dis, meaning “two,” and polos, meaning “pole”).