How can you measure the melting point of a solid in a classroom?

• A. Gradually heat a solid and record the temperature at which it changes to a liquid.
• B. Boil the solid and record the boiling point.
• C. Cool a liquid until it freezes.
• D. Dissolve the solid in water and measure conductivity.

Answer: (A)

Melting point is the temperature at which a solid becomes a liquid. To measure it in class, heat a small sample slowly and in small temperature steps, recording the temperature as soon as the solid begins to flow and, ideally, when it has completely turned into liquid. For a pure substance, melting occurs at a single sharp temperature; impurities usually create a melting range. A common classroom method uses a tiny sample in a capillary tube on a hot stage with a thermometer, but any careful gradual heating works. This approach is about melting, not boiling a solid—which isn’t how melting is defined for most solids—nor about cooling a liquid to freeze or dissolving a solid in water and measuring conductivity, which relate to freezing or solubility, not melting.