Question

Is removing salt from water by evaporation considered a physical or chemical change?

Answer 1

Physical changes are largely changes of state........

Explanation:

......so removing water from a salt solution by distillation would be regarded as a physical change.

Answer 2

In my opinion, chemical change.

Explanation:

This is where standard school chemistry and things like "Physical change = reversible, chemical change = non-reversible" falls down. The definition of a chemical change is one in which the chemical structure of a substance changes (i.e. there are bonds broken and/or formed).

Dissolving salt in water does in fact cause a change in chemical structure - the crystalline structure of sodium and chlorine ions in a lattice changes to completely separate sodium ions and chloride ions, each fully solvated by water molecules. This is, of course, a change in physical form, but it is also a change to the chemical formula (NaCl (s) changes to Na+ (aq) and Cl- (aq) - the Na+ and Cl- no longer linked).

It is, of course, reversible - heat the solution to drive off the water and you end up with solid NaCl again - but as I mentioned above, it is not the case that chemical changes are nessarily irreversible.

So I would judge this to be a chemical change - it isn't a change you can effect simply by changing physical properties - you need to have the water present too.