Explain whether or not each of the following pairs of solvents might be useful as a solvent pair for recrystallization.

(a) ethanol-methanol (b) hexane-cyclohexane (c) acetone-ethanol
(d) water-ethanol (e) water-cyclohexane

You need to solvents one of which is excellent, the other poorer. So it depends on the solute, but I doubt e solvents both dissolve the same solute. The others will depend on the solute.

and, of course, as DrBob just pointed out to me, e solvents are NOT miscible, which they must be.

thanks. i understand why e won't work, but im a little confused on choice a. they both dissolve a wide range of solutes so would it be a great solvent?

well im confused because you said one needs to be great and the other has to be poor. so if you combine both do you get a great solvent or a horrible one?

To determine whether a pair of solvents is useful for recrystallization, we need to consider a few key factors: solubility of the solute at different temperatures, polarity of the solvents, and similarity in boiling points. Here's how each pair can be analyzed:

(a) ethanol-methanol:
Both ethanol and methanol are polar solvents with similar boiling points. This pair can be useful for recrystallization if the solute is soluble in both solvents at high temperatures and less soluble at lower temperatures.

(b) hexane-cyclohexane:
Hexane and cyclohexane are nonpolar solvents with similar boiling points. Generally, recrystallization is not effective with nonpolar solvents because they have low solubility for many organic compounds. This pair may not be suitable for most recrystallizations.

(c) acetone-ethanol:
Acetone is a polar solvent, while ethanol is a slightly polar solvent. This pair can be useful if the solute is soluble in acetone at high temperatures and less soluble in ethanol at lower temperatures. The difference in polarities between the two solvents can help in achieving better purification.

(d) water-ethanol:
Water is a highly polar solvent, while ethanol is a polar solvent. This pair is commonly used in recrystallization since water has a high solubility for many polar organic compounds, while ethanol helps to dissolve polar impurities. The difference in polarities aids in purification.

(e) water-cyclohexane:
As mentioned before, nonpolar solvents like cyclohexane are generally not suitable for recrystallization. Water is highly polar and has a high solubility for many polar compounds. Hence, this pair is not likely to be useful for recrystallization.

In all cases, it is important to consider the solute's solubility characteristics and choose solvents that are appropriate for achieving purification and crystallization. Performing solubility tests at various temperatures can help determine the suitability of a solvent pair for recrystallization.