Final answer:
Reusing a sample for melting point determination can introduce impurities, thus affecting the accuracy of the results. It might also violate laboratory safety protocols designed to prevent cross-contamination.
Step-by-step explanation:
When considering why a sample should not be reused in a melting point determination, there are multiple reasons that could affect the results. A key concern with reusing a sample is the introduction of impurities which can lower the melting point, as impurities disrupt the regular lattice structure of a crystalline solid and require less energy to melt. This concept is supported by historic experiments, such as those conducted by Hall and Heroult with aluminum compounds, showing that a 5% mixture of Al2O3 in cryolite significantly reduced the melting point.
Moreover, reusing samples in a melting point apparatus may be prohibited if the samples are designed to be single-use. This prevents cross-contamination and maintains laboratory safety protocols. It's important to ensure samples are pure and that safety guidelines are followed to obtain accurate melting points and avoid any laboratory accidents.