A student wants to find out whether a sample of a white solid is a pure substance or a mixture. Describe how the student could use melting point data to determine this, and explain what results would be expected for a pure substance compared to a mixture.

Heat the solid and record the temperature at which it begins to melt. A pure substance will melt at a single, sharp temperature – a narrow range of about 1 °C. A mixture will melt over a broader range of temperatures, showing a gradual change from solid to liquid. Compare the measured melting point with the known value for the suspected pure substance; if they match and the transition is sharp, the sample is pure. If the measured point is lower or shows a range, the sample is a mixture.