Question

What is the color of anhydrous copper sulphate?

Answer 1

First we need to know what it means by the term anhydrous. When a crystalline substance loses water, the compound is said to be an anhydrous compound. A crystalline substance can lose its water molecule by various methods like heating, freeze-drying, vacuum, desiccators, etc. to form an anhydrous compound.

Complete answer:
Now, crystalline copper sulfate has the formula $CuS{{O}_{4}}.5{{H}_{2}}O$.
Or we can say that when a copper derivative like cupric oxide (CuO), cupric hydroxide ($Cu{{(OH)}_{2}}$), or cupric carbonate ($CuC{{O}_{3}}$) is added to dilute hydro sulfuric acid (${{H}_{2}}S{{O}_{4}}$), the copper is hydrated to form a blue vitriol or hydrated copper (II) sulfate ($CuS{{O}_{4}}.5{{H}_{2}}O$).
This blue vitriol formed is a pentahydrate and has a molar mass of 249.685 g/mol. It is soluble in water and is non-combustible.
Now, when this hydrated copper (II) sulfate ($CuS{{O}_{4}}.5{{H}_{2}}O$) or blue vitriol is heated at high temperatures, it loses its water of crystallization ($5{{H}_{2}}O$) and forms amorphous copper sulfate ($CuS{{O}_{4}}$).
The blue vitriol turns white upon heating.
Hence, the color of amorphous copper sulfate ($CuS{{O}_{4}}$) is white.
Amorphous copper sulfate ($CuS{{O}_{4}}$) has a powdery texture and has a molar mass of 159.60 g/mol. It decomposes at a temperature of 383 K.

Note:
It should be noted that when water is added to the white amorphous copper sulfate ($CuS{{O}_{4}}$), it regains its water of crystallization to form hydrated copper (II) sulfate ($CuS{{O}_{4}}.5{{H}_{2}}O$) or blue vitriol.