Question

2 multiple choice 1 point in mixed-solvent recrystallization, why must the two solvents be miscible? to avoid phase separation and allow uniform solubility adjustment to decrease boiling point drastically to increase melting point of crystals to ensure they form layers during filtration

Explanation:

• For the option "To avoid phase separation and allow uniform solubility adjustment": In mixed - solvent recrystallization, if the two solvents are miscible, they form a single phase. This prevents phase separation, and since they are uniformly mixed, we can adjust the solubility of the solute in a controlled and uniform way by changing the ratio of the two solvents.
• For "To decrease boiling point drastically": The miscibility of solvents in recrystallization is not related to drastically decreasing the boiling point. The main goal of recrystallization solvents (miscible or not in the context of the wrong option) is about solubility of the solute, not boiling point reduction.
• For "To increase melting point of crystals": The miscibility of the two solvents in the recrystallization process does not have a direct relation to increasing the melting point of the crystals. The melting point of the crystals is an inherent property of the solute compound, and the solvents are used for dissolving and recrystallizing, not altering the melting point in this way.
• For "To ensure they form layers during filtration": If the solvents were immiscible, they would form layers, but in mixed - solvent recrystallization, we want a homogeneous mixture (so miscible solvents) to control solubility, not to form layers during filtration. Layers during filtration would be a problem as it would disrupt the recrystallization process.

Answer:

A. To avoid phase separation and allow uniform solubility adjustment