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Thread: boiling points

  1. #1 boiling points 
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    hi guys quick question

    i am comparing two compounds and the boiling points...
    just wondering as well as other properties does solubility affect why one would be higher to another?

    thanks


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    Why would solubility affect the boiling point of a pure substance? It is (mainly) down to intermolecular forces and molecular weight.


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  4. #3  
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    Are you asking about azeotropes?

    Edit:Maybe this Wikipedia page about Raoult's law will help.
    Raoult's law - Wikipedia, the free encyclopedia
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  5. #4  
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    Quote Originally Posted by PhDemon View Post
    Why would solubility affect the boiling point of a pure substance? It is (mainly) down to intermolecular forces and molecular weight.
    Why does height affect the boiling point of say, water?
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  6. #5  
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    The boiling point of a liquid is elevated by dissolved particles in the solution. So I would think that if you had two saturated solutions with two different materials dissolved in them, the one with the higher solubility would have a higher boiling point. Wouldn't it? I will defer to PhDemon's superior knowledge on this one.
    Boiling-point elevation - Wikipedia, the free encyclopedia
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    Quote Originally Posted by Write4U View Post
    Quote Originally Posted by PhDemon View Post
    Why would solubility affect the boiling point of a pure substance? It is (mainly) down to intermolecular forces and molecular weight.
    Why does height affect the boiling point of say, water?
    I didn't see anybody mention height, but water boils at lower temperature at higher elevation, because of the lower atmospheric pressure.
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  8. #7  
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    Harold beat me to it, but you seem to have a habit of posting irrelevancies, what does height (or pressure) have to do with the OP or my response?
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  9. #8  
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    Quote Originally Posted by PhDemon View Post
    Harold beat me to it, but you seem to have a habit of posting irrelevancies, what does height (or pressure) have to do with the OP or my response?
    I thought it might be relevant, but apparently height, gravity, and pressure all are irrelevant and can be ignored in context of the OP question. Sorry about that.
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  10. #9  
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    Quote Originally Posted by Write4U View Post
    Quote Originally Posted by PhDemon View Post
    Harold beat me to it, but you seem to have a habit of posting irrelevancies, what does height (or pressure) have to do with the OP or my response?
    I thought it might be relevant, but apparently height, gravity, and pressure all are irrelevant and can be ignored in context of the OP question. Sorry about that.
    Just to close this out, what may help is to appreciate that the boiling point is the point at which bubbles of vapour can form within the body of the liquid. This is possible only once the vapour pressure equals that of the ambient pressure above the surface of the liquid. So, if you reduce atmospheric pressure by moving to higher altitude, boiling can occur at a lower temperature.
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  11. #10  
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    Quote Originally Posted by tecnica View Post
    hi guys quick question

    i am comparing two compounds and the boiling points...
    just wondering as well as other properties does solubility affect why one would be higher to another?

    thanks
    If you speak of solubility you need to say what solvent you have in mind. If you mean water, then I suppose it is true that water, being a polar solvent is able, unlike non-polar solvents such as benzene or n-hexane, to dissolve quite a number of ionic solids, which as a rule have high BPs.

    But then, there are examples of high BP ionic solids with poor solubility in water (BaSO4 springs to mind). And there are also plenty of low BP substances that also dissolve in water very well. Ethanol is a good example.

    So I'm not sure this is a very helpful line of enquiry, though you could make a nice essay out of considering the issues behind it.
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  12. #11  
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    Going back to what Harold put up in post #5.
    I am not sure I quite understand the vapour pressure of the solvent being reduced because it was diluted by whatever was dissolved in it.
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  13. #12  
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    Quote Originally Posted by dan hunter View Post
    Going back to what Harold put up in post #5.
    I am not sure I quite understand the vapour pressure of the solvent being reduced because it was diluted by whatever was dissolved in it.
    The Wiki link he gave explains this. But think of how vapour pressure arises. It is due to the rate at which molecules at the surface of the liquid acquire enough energy to escape from the intermolecular attraction and go into the vapour space above. If some of the molecules at the surface are not solvent molecules but involatile solute molecules, then the rate at which solvent molecules escape is lower, due to the blocking effect of these involatile molecules taking up space on the surface. So only when the mean kinetic energy of the mixture has gone up a bit more will the vapour pressure equal the value for the pure solvent. And higher mean k.e. means higher temperature.

    It's just Raoult's Law in the case where one component has a VP close to zero.
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  14. #13  
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    Quote Originally Posted by tecnica View Post
    hi guys quick question

    i am comparing two compounds and the boiling points...
    just wondering as well as other properties does solubility affect why one would be higher to another?

    thanks
    Getting back to the original question, and some of the additions already made.

    Stuff that affect boiling point are outer pressure, hydrogen bonds, material purity, presence of nucleation sites, acceleration or gravity, and the mass.

    Heat shakes a molecule/atom until the bonds, or the gravity or whatever force keeps the fluid together fails, and chunks fly off in a gaseous state. Sometimes a material will oxidize before vaporizing, so that material will either have an estimated boiling point, or it was simply boiled in a nitrogen/argon atmosphere.
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  15. #14  
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    I think volatility of the solute is the property that may affect the boiling point, not solubility. Solubility just describes how much of the solute will dissolve in amount solvent.
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  16. #15  
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    Volatility is quantified as the vapour pressure, this is pressure exerted at a particular temperature by a vapour in equilibrium with a condensed phase. The boiling point is temperature at which the vapour pressure equals the ambient atmospheric pressure so the boiling point and volatility are obviously related. Edit, I see exchemist gave this information earlier...
    Last edited by PhDemon; August 29th, 2014 at 03:11 AM.
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  17. #16  
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    If you upset a redhead, you will learn all about boiling points.
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  18. #17  
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    Seriously, all I know is that at higher elevations it takes longer.
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  19. #18  
    Bullshit Intolerant PhDemon's Avatar
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    What takes longer? At higher elevations, boiling points are lower as the ambient atmospheric pressure is lower, this means the vapour pressure of a substance equals the ambient pressure at a lower temperature than at sea level.
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  20. #19  
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    Quote Originally Posted by babe View Post
    Seriously, all I know is that at higher elevations it takes longer.
    Your right it does take a lot longer to cook something at higher altitudes.

    This is because the vapor pressure becomes equivalent to the lower atmospheric pressure (lower atms than what we experience at sea level) at a much quicker rate. With less input of energy, therefore the boiling point of water at a higher elevation (<1atm) occurs at a much lower temperature than 100 C.

    Thus it takes longer to fully cook your meal!
    Last edited by AndresKiani; August 29th, 2014 at 04:44 AM.
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  21. #20  
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    Quote Originally Posted by PhDemon View Post
    What takes longer? At higher elevations, boiling points are lower as the ambient atmospheric pressure is lower, this means the vapour pressure of a substance equals the ambient pressure at a lower temperature than at sea level.
    She's right though, it does take a longer to prepare food at a higher elevation.
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  22. #21  
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    Quote Originally Posted by AndresKiani View Post
    Quote Originally Posted by PhDemon View Post
    What takes longer? At higher elevations, boiling points are lower as the ambient atmospheric pressure is lower, this means the vapour pressure of a substance equals the ambient pressure at a lower temperature than at sea level.
    She's right though, it does take a longer to prepare food at a higher elevation.
    That has been my experience when in altitudes having been before car wreck, a major downhill skier. Cooking always took longer!!!
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  23. #22  
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    Yes she is but, it wasn't clear what she was talking about...
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  24. #23  
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    I suppose the effect of increased altitude is the opposite of a pressure cooker. Since childhood, I have wondered what the pressure did [directly] to help cook the food, but I see now it's the wrong line of thought. I see now that the pressure allows the temp to increase beyond 212F/100C, thus shortening the cooking time. Aha!
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  25. #24  
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    Yep, that's it.
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    Quote Originally Posted by jrmonroe View Post
    I suppose the effect of increased altitude is the opposite of a pressure cooker. Since childhood, I have wondered what the pressure did [directly] to help cook the food, but I see now it's the wrong line of thought. I see now that the pressure allows the temp to increase beyond 212F/100C, thus shortening the cooking time. Aha!
    Yeah, at high enough altitudes, you can not even boil a potato without using a pressure cooker. BTW, I LOVE pressure cookers. Time and energy efficient for sure.
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    I use big time high tech pressure cooker for my tuna and marinara.....trust me......but never at an altitude.
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    Quote Originally Posted by babe View Post
    I use big time high tech pressure cooker for my tuna and marinara.....trust me......but never at an altitude.
    Not in the same dish, right? I am not so sure tuna goes all that well with marinara?
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  29. #28  
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    Quote Originally Posted by babe View Post
    If you upset a redhead, you will learn all about boiling points.
    Of course, red heads have higher body temperature and it takes very little to reach boiling point.
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  30. #29  
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    Quote Originally Posted by Write4U View Post
    Quote Originally Posted by babe View Post
    If you upset a redhead, you will learn all about boiling points.
    Of course, red heads have higher body temperature and it takes very little to reach boiling point.

    We tend to blow up...but making up is
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