Chemistry - Is dehydrating copper(II) sulphate pentahydrate a chemical or physical change?

Solution 1:

The traditional answer is that it's a chemical change when bond-making and bond-breaking is involved. The material certainly changes appearance, and heating copper sulphate somehow releases bound water.

That said, bonding in metal-aquo complexes runs the gamut from very weak to exceedingly strong - exchange rates span 15 orders of magnitude (Fig. 1 in Jan Reedijk, Metal-Ligand Exchange Kinetics in Platinum and Ruthenium Complexes. Platinum Metals Rev. 2008, 52, 2–11. DOI: 10.1595/147106708X255987), and where do you draw the line between a "physical" electrostatic interaction (in, say, $\ce{Na(OH_2)_6^+}$) and a chemical bond (as seen in $\ce{Cr(OH_2)_6^3+}$?

Solution 2:

You heated copper(II) sulfate until it turned white. This is a quite simple chemical reaction:

\begin{align} \ce{\underset{(blue)}{CuSO4.5H2O} &->[][100 ^\circ C] CuSO4.H2O + 4 H2O}\\ \ce{CuSO4.H2O &->[][> 200 ^\circ C] \underset{(white)}{CuSO4}} \end{align}

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Solution 3:

According to one text,^[1] a change in color, release of a gas (and some other changes), are indications of a chemical reaction. Since water vapor is released and the solid changes color, this should be considered as a chemical reaction, not a physical change.

[1] Wikibooks, General Chemistry/Properties of Matter/Changes in Matter