Question #e788e

2 Answers
David Drayer
Jul 6, 2017

A salt solution is not a pure substance because it can be broken down into salt and water by a physical change.

Explanation:

Pure substances can only be separated by a chemical change, and elements not even by a chemical change.

Mixtures and solutions are not pure substances. Mixtures and solutions can be separated by physical changes.

Simon Moore
Jul 6, 2017

Because it contains more than one distinct chemical species.

Explanation:

A pure substance contains only one type of atom, or one type of molecule (or in the case of ionic compounds, one specific ion pair).

So common salt itself is a pure substance (it contains only sodium chloride, NaCl) and pure water (as opposed to sea water, or water with additives in it) is a pure substance, it contains only #H_2O# molecules.

But common salt solution is a mixture of water molecules and solvated #Na^+# and #Cl^-# ions, more than one distinct chemical species, and therefore not a pure substance.

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