Under what condition might the observed melting point of a sample be higher than expected?

The observed melting point of a sample might be higher than expected when using a calibrated thermometer. A calibrated thermometer ensures accurate temperature readings by compensating for any intrinsic errors or deviations that may occur in measurement instruments. If the thermometer is properly calibrated, it provides reliable results, reflecting the correct temperature at which the sample transitions from solid to liquid.

In contrast, if other factors come into play—such as the presence of impurities, inadequate cooling, or excessive sample size—they typically tend to lower the melting point or broaden the melting range. Impurities disrupt the lattice structure of a crystalline solid, which generally lowers the melting point. Inadequate cooling could prevent complete solidification, leading to inaccurate observations. An excessive sample size might also contribute to uneven heat distribution within the sample, affecting melting observations.

Thus, using a calibrated thermometer, which maintains accuracy, can yield a melting point reading that appears higher than expected when compared to standard references that may not take into account any measurement discrepancies.