Vapor Pressure of Solutions

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Medgen

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I am a little confused about how vapor pressures of solutions. Here is my understanding: when you have two substances and only one them is volatile, then you can employ a simple application of Raoult's law. The same goes for when you have two volatile substances that do not interact with each other (ideal solution). If the mixing of the solutions is exothermic or endothermic, then you have an azeotrope with a new boiling point that can only be separated by fractional distillation. But in this case of mixing two volatile substances (and you have an ideal solution), there will be a new vapor pressure, so would the liquid mixture boil at a different temperature or would each substance vaporize separately? So in this case, simple distillation could be employed.

Thanks!!!

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I am a little confused about how vapor pressures of solutions. Here is my understanding: when you have two substances and only one them is volatile, then you can employ a simple application of Raoult's law. The same goes for when you have two volatile substances that do not interact with each other (ideal solution). If the mixing of the solutions is exothermic or endothermic, then you have an azeotrope with a new boiling point that can only be separated by fractional distillation. But in this case of mixing two volatile substances (and you have an ideal solution), there will be a new vapor pressure, so would the liquid mixture boil at a different temperature or would each substance vaporize separately? So in this case, simple distillation could be employed.

Thanks!!!

First of all in ideal solutions the two volatile substances do interact it is just assumed that those interactions between the two substances are the same as within themselves.

The mixture will boil at a certain temperature based on its new vapour pressure. What changes and allows distillation is that the vapour will have a different composition than the solution. The vapour will have more of the more volatile substance. So if A is more volatile than B the vapour will have more A than B. This means that the remaining liquid will have more B than A. Since the composition of the liquid has changed it now has a different boiling point. This is the idea behind simple distillation, while fractional distillation repeats this many times. If you keep doing this over and over your going to get a solution pure in B. Azeotropes are points where distillation cannot be used because the composition of vapour and the composition of the solution are the same so its impossible to seperate. This is the reason why 200 proof alcohol doesn't exist. There is an azeotrope in the distillation of alcohol.
 
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