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Do pH levels carry on thorugh evaporation?

  1. Feb 16, 2005 #1
    I need to know:

    In a closed system sealed off from outside air, if water from a mass of basic water evaporates, will the pH of the air be affected? If so, when the air condenses, how wil the pH of soil in the closed system be affected?

    Thanks for the help.
     
  2. jcsd
  3. Feb 16, 2005 #2

    Gokul43201

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    "Is the pH of the air affected ?" No, it is not. You do not have free ions in the vapor - at least, not that I'm aware of.

    To answer any more will require that the question be restated more clearly providing more information about the system of interest, as well as what your specific concern is.
     
  4. Feb 16, 2005 #3

    dextercioby

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    That's an interesting part with the "pH of the air"...U'll have to specify what the chemical composition of that air is:normally,for open air,the pH is very,very close to 7,coming from the acid part..,due to various acid anhydrides (from industrial area) and water molecules...But the way you set the problem,i highly doubt that the air in a closed system in which water eveporates contains anything but N_{2},O_{2} & water vapors...Sure,it's CO_{2} as well (that tiny "regulamentar" bit of 0.03%) which would make the pH not exactly 7,but 6.very many nines.

    Daniel.
     
  5. Feb 17, 2005 #4

    Gokul43201

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    Dexter, I can't see how having carbon dioxide in the air reduces its pH (in fact, I can't see how you could sensibly define pH for a gas, in a manner that is useful). Where are the hydrogen ions coming from ? And how do you define their concentration ? (per liter of air ?) Now if you have CO2 dissolving in rain water, then this rain water will be acidic because the dissolved CO2 aids in ionization.

    I have never heard of pH in gases, and this may just be a due to my rather unstructured education. If you know of some link, I'd like to look at it.
     
  6. Feb 17, 2005 #5

    dextercioby

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    Yes,you're right...Misthinking with the parallel with acid rains...Which as you said,imply gases dissolving in water and creating very weak acid sollutions...

    Yes,by definition pH is for solutions,which means that gases would have to fit in only by dissolving into a solvent.

    Sorry.My affirmations were not as accurate as they were intended...

    Daniel.
     
  7. Feb 17, 2005 #6

    Monique

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    It would depend on what the CO2 concentration of the air is, and how it is affected by the basic water.

    CO2 in air will dissolve over time into water and created [H2CO3], which is an acid. I've seen this affect where dH2O water that starts with pH7.0 will over time acidify due to dissolving CO2.

    So, the water won't change the pH of air: there are no free hydronium (H3O+) in air. But indirectly it might change the CO2 concentration.. but I'm not sure whether more CO2 would dissolve in basic water than in acidic water.
     
  8. Feb 17, 2005 #7

    GCT

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    pH usually pertains to the acidity (or basicity rather) in aqueous solutions, that is the ability of a specific compound in water to affect the following net equation:

    H+ + 0H- --->H20, pH is derived from the K of this equation.

    Thus when referring to pH, it is specifically for aqueous solutions. I believe that considerable amount of water is required if one wishes to consider the pH in aq solutions; that is if we wish to apply Ka.......in which water is neglected.

    For instance, one could propose that high concentrated sulfuric acid, will have a higher pH. However, it does not.......can you guess why? After you answer this questions, apply it to your situation in the context of water vapor.
     
  9. Feb 17, 2005 #8

    GCT

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    Yeah, in addition to Moniques explanation, C02 is an acidic oxide, frequently acidic are oxides of a non-metallic element and as you can guess basic oxides-metals-and amphoteric oxides exist also. With the proposal that C02 increases pH of an aqueous solution, on can guess that it would dissolve better in basic solutions, one way to expalin this is by common ion effect (if you can trace process out in the long run, you'll see that having a basic solution can indirectly affect the solubility of C02). This is all in theory, my opinion, an expert might disagree stating a factor which I have not heard of.
     
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