Dissolving Salt in Water: Chemical or Physical Change?

When you dissolve table salt (sodium chloride, also known as NaCl) in water, are you producing a chemical change or a physical change? Well, a chemical change involves a chemical reaction, with new substances produced as a result of the change. A physical change, on the other hand, results in a change of the material’s appearance, but no new chemical products result.

Why Dissolving Salt Is a Chemical Change

When you dissolve salt in water, the sodium chloride dissociates in Na+ ions and Cl ions, which may be written as a chemical equation:

NaCl(s) → Na+(aq) + Cl(aq)

Therefore, dissolving salt in water is a chemical change. The reactant (sodium chloride, or NaCl) is different from the products (sodium cation and chlorine anion).

Thus, any ionic compound that is soluble in water would experience a chemical change. In contrast, dissolving a covalent compound like sugar does not result in a chemical reaction. When sugar is dissolved, the molecules disperse throughout the water, but they do not change their chemical identity.

Why Some People Consider Dissolving Salt a Physical Change

If you search online for the answer to this question, you’ll see about an equal number of responses arguing that dissolving salt is a physical change as opposed to a chemical change. The confusion arises because of one common test to help distinguish chemical changes from physical ones: whether or not the starting material in the change may be recovered using only physical processes. If you boil the water off of a salt solution, you’ll obtain salt.

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