Is water a solvent in this problem?

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Discussion Overview

The discussion revolves around the classification of water as a solvent or solute in a solution of water dissolved in methanol, specifically when the mole fraction of water is 0.25. The scope includes conceptual clarification related to solution chemistry and definitions of solute and solvent.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether water is a solvent or solute in the given problem, noting the phrasing "a solution of water dissolved in methanol."
  • Another participant suggests that the mole fraction indicates that methanol must be the solvent since it has a higher mole fraction (0.75) compared to water (0.25).
  • A participant reflects on the common rule that the solvent is present in greater quantity, suggesting this scenario may be an exception.
  • Further clarification is provided using the example of a typical aqueous solution, emphasizing the relative concentrations of solute and solvent.

Areas of Agreement / Disagreement

Participants express differing views on the classification of water and methanol, with some suggesting that methanol is the solvent based on mole fractions, while others consider the phrasing of the problem as potentially misleading. The discussion remains unresolved regarding the classification of water in this context.

Contextual Notes

Participants highlight the importance of mole fractions in determining the roles of solute and solvent, but there is no consensus on whether the phrasing of the problem creates an exception to the typical definitions.

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Homework Statement
Determine the molality of a solution of water dissolved in methanol for which the mole fraction of water is 0.25.

Hi all,
I just want to ask if water in this problem is a solvent or a solute!? Is water always a solvent even though they say "a solution of water dissolved in methanol" in the problem? Please help me clear it up.
 
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It appears you've answered your own question. Also, note the mole fraction of water in the solution.
 
naele said:
It appears you've answered your own question. Also, note the mole fraction of water in the solution.

Thanks! Yes, and that's how it get me confused. A solvent is what we have more of, and a solute is what we have less. This appears violating the common rule. I think this is an exception right? what do you think?
 
Last edited:
That's basically how you look at it. Consider a typical aqueous solution, say 1M HCl. That means there's one mole of HCl in one liter of water. But water is at roughly ~55M so there's quite a bit more of it. In this case, we're told that a water/methanol solution has water at 0.25 mole fraction. By extension we know that methanol has to be 1 - 0.25 = 0.75 which of course is greater than 0.25 so we can only conclude that methanol is the solvent here.
 
Yes, that makes sense to me! Thank so much!
 

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