Where the
world gathers for metal finishing
Q&As since 1989


-----

Different colors of CuSO4

2002

Dear Sir,

Why is hydrated copper sulphate [on eBay or Amazon] blue in colour, while anhydrous copper sulphate has a white colour? How is the formation of a crystalline structure, upon hydration give CuSO4 the blue colour?

Thank you,

Sushila [last name deleted for privacy by Editor]
- Salmiya, Kuwait

---

The blue colour is due to the water of crystallization (CuSO4.5H2O). When this is removed by heating, basic copper sulphate is left (CuSO4.H2O) and this can be further broken to simple CuSO4. It is essential you realise the water is not there as free liquid, but as a molecule in its own right and it is bound to the copper atom. These molecules fulfill a structural role in as much as they fill voids in the crystal structure and let the salt ions take up a regular and therefore crystalline, shape of minimal energy content. In the case of all transition metals, the water of hydration is linked to the d (or higher) orbitals and these distort slightly, thereby causing a band energy shift that is characterised by the colour. In the case of copper this shift is in the 600-900 nm region and this is where the blue-green colours occur. The envelopes of these bands are generally unsymmetrical and encompass several overlapping transitions.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2002

Four out of the five water molecules held per formula unit of the salt CuSO44.5H2O are attached by coordinate covalent bonds to the copper ion. The fifth water molecule is attached to the sulphate ion but by a different mechanism. I want to know how a molecule might be bonded to a sulphate ion.

Bushier Zubair Dauda
industrial trainer - UNIVERSITY CITY, SHARJAH, UAE
2004

How is lime carried through rock?

Matthew Li
- Australia, Victoria, Melbourne
2004

---

2005

Dear sir/madam

Can anyone tell me how copper(ll)sulphate is produced? or can someone tell me from what reactions it comes?

Please tell me.

Thank you,

Andrea Djezen
- Amsterdam, Noord Holland, Netherlands

What sort of bonding occur when copper sulphate is hydrated and is this then a complex? If so why is there a dot before the 5 and not brackets being used?

Crystallia Adams
- Nassau, Bahamas
2006

Why the CuSO4.5H2O is In blue color,and without water in CusO4 is in green color?

Hemalatha
- Tirupati, Andhra Pradesh, India
2006

How does the structure of the CuSO4 crystal change after the water has been lost?

Haley Bloom
- Plainview, New York
2007

After the copper sulphate has been heated it goes to amorphous powder, it is no longer a crystal and it changes from blue to white.

Shauna Ebanks
- Long Bay, Portland Jamaica
March 4, 2008

---

March 23, 2008

hello one and all... I am Sathwik Gowda, pursuing my master degree in management at BMS college, Bangalore.

I would like to know how the crystal CuSO4 is produced and what are the main and other possible uses of it. As I am at the end of my course, I want to be a self employed person. I want to be a job creator rather a job seeker.

ThanQ ALL....

Sathwik Gowda
- Bangalore, Karnataka, India

To produce CuSO4 add excess (more than needed) CuO and heated H2SO4, filter to remove excess CuO and the heat to drive off the water rinse the salt and dry,

Eva Joseph
- New York
May 11, 2009