Why can't simple distillation be used to separate two solutes?

[markymark71990]

Can someone explain to me the following answer they are giving me?

Simple distillation is employed to separate two miscible liquids, because they have different boiling points. In attempting to distill one solute from the other, it is likely that the solvent would boil away rather than a solute. The result is that simple distillation cannot be used to separate two solutes.

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[Sammy1024]

Simple distillation is used when the two compounds have a boiling point of greater than 25°C difference. So if in the problem, the two had boiling points that were very close like 10°C apart, you may have to use fraction distillation or some other distillation method.

 

[markymark71990]

All the question asked was "which if the following techniques would be used to separate two solutes" They had distillation crystallization column chromatography and TLC. I chose crystallization. Just a poorly worded question IMO

 

[markymark71990]

would NOT be used**

 

[Sammy1024]

If that's the case, then ya, it's probably a poorly worded question. I don't know how you could tell without any other data.

 

[DrknoSDN]

I'm going to say it's not poorly worded. (sorry), 😵

If you have a solvent that contains 2 other solutes, it would be hard/impossible to separate them out via distillation.
Like it said, distillation is normally used for when the majority of the liquid is one of the two desired liquids. If 2 solutes are dissolved in a third solvent the vast majority of the liquid your attempting to distill is not going to be of interest.

Maybe when you saw 2 solvents you were thinking only 2 liquids by themselves, instead of 2 liquids that are miscible with a 3rd solvent?

 

[markymark71990]

Why exactly is that the case? Do the two individual solutes form a solution with a uniform boiling point?

 

[DrknoSDN]

I don't believe so, but the boiling point of the solutes would be masked by the solvent because of a low percent of solute at the surface that is able to escape as vapor.

Rationalization:
Even a 10/10/80% mixture would only have 10% of surface molecule able to form vapor at the lowest boiling point. Also there would need to be vary different boiling points for all liquids like Sammy said. The Lower BP and higher BP solute would need to be very different, and both much lower than the solvent. That's also assuming a high percent of solutes. A 1/1/98% mixture or lower would be more unreasonable, whereas any percent of two miscible liquids can be separated if adequate BP differences are present.