If you recrystallize a compound with a 1/2 ethanol/water mixture and water remains in the compound after recrystallization, would that change the melting range of the pure compound?

Yes.

To determine whether the presence of residual water in a recrystallized compound would affect its melting range, we need to consider the principles behind recrystallization and the properties of the compound in question.

Recrystallization is a commonly used purification technique to obtain a pure compound from an impure mixture. It relies on the differences in solubility between the desired compound and impurities. The compound is dissolved in a suitable solvent at an elevated temperature, and then slowly cooled, forcing the compound to crystallize out of the solvent. In an ideal scenario, all impurities are left behind in the solvent, resulting in a purer compound.

In this case, you used a mixture of 1/2 ethanol and water as the solvent for recrystallization. Water is a relatively polar solvent, while ethanol is less polar. By using a mixture of the two, you create a solvent with intermediate polarity, which can improve the solubility characteristics for a wide range of compounds.

Now, if water remains trapped within the recrystallized compound, it would occupy spaces in the crystal lattice structure. The presence of water molecules within the crystal could potentially alter the packing arrangement of the compound's molecules and lead to changes in the physical properties of the crystal, including the melting range.

However, the extent of the change in the melting range would depend on several factors, such as the amount of residual water, the specific compound being recrystallized, and the crystalline structure of the compound. In some cases, the impact on the melting range may be negligible, while in others, it could be more significant.

To accurately determine the effect of residual water on the melting range, it is advisable to compare the melting ranges of the pure compound (without any residual water) and the recrystallized compound. Conducting a differential scanning calorimetry (DSC) or melting point analysis for both compounds under controlled conditions would provide valuable information about any differences in their melting behavior.

In summary, the presence of residual water in a recrystallized compound could potentially alter its melting range, although the extent of the change would depend on multiple factors. Performing a comparison with the melting range of the pure compound would help assess any variations caused by the presence of residual water.