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Trying to settle an arguement

  1. Apr 18, 2009 #1
    Looking for some help with this one...

    I'm having an arguement with a friend of mine, a supposed graduate of Purdue (Aero Eng) who seems to think that all one has to do to make hydrochloric acid (admittedly, a weak one) is to mix table salt with water:

    NaCl + H2O > HCl + NaO

    I admit that it has been a long while since I took engineering chemistry, but this is a ridiculous assertion. First off, the chemical equation isn't balanced, second, there has to be some sort of catalytic reaction to promote this, and third, the most obvious, I'd get acid burns everytime I went to the beach.

    Could someone please give me supported evidence that I can use to convince this guy that just because it is on paper doesn't make it so? Also, is seawater in fact, acidic? At the same time, if I'm wrong, I'd like to know that as well.

    I look forward to hearing from you.
     
    Last edited: Apr 18, 2009
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  3. Apr 18, 2009 #2

    mgb_phys

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    You could argue that you make HCl but at the same time you make an equal amount of NaOH . In fact you make a mix of Cl-, OH-, Na+ and H+ ions
     
  4. Apr 18, 2009 #3

    GCT

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    The first thing that happens is that the sodium and chloride become ions that are hydrated by water , hydrochloric acid is considered to dissociate completely in water ... anyways here is a similar equation except that it is switched

    HCl + NaOH --> H2O + NaCl

    the reverse does not happen basically .
     
  5. Apr 18, 2009 #4

    Borek

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    Pure water contains 10-7mol/L H+. If you dissolve NaCl in the water, you can say you have 10-7mol/L HCl solution.

    At the same time - or exactly the same reason - you will have 10-7mol/L NaOH solution.

    That's just more quantitative way of stating what mgb_phys already wrote.

    But your solution is still perfectly neutral, neither basic nor acidic.

    Well... for nitpickers, it is a little bit acidic, but not because you have added Cl-, but because of the Na+ presence. But that's a slightly different story :wink:
     
  6. Apr 20, 2009 #5
    While I appreciate the answers so far, I was hoping for something a bit less technical. Talking about mols won't do any good with this guy because to him, mols burrow in his yard.

    Can anyone out there answer the question in layman's terms? Again, thanks for the answers, but I need to be able to explain the fallacy of his thoughts...
     
  7. Apr 20, 2009 #6

    mgb_phys

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    In simple terms - you don't make the water acidic because as well as HCl you make an equal amount of NaOH (which is alkali)
    From a chemical definition point of view you don't make any NaOH or HCl anyway because it's not energetically favourable for them to come together like that - you just make a mixture of Na,OH,H,Cl ions
     
  8. Apr 20, 2009 #7
    Another possibility (but just another way to say what others have already said): you could say that both reactions happens:

    1. 2NaCl + H2O --> 2HCl + Na2O

    2. 2HCl + Na2O --> 2NaCl + H2O

    But the second has an *enormously* greater potential to happen than the first, so, at equilibium, you have NaCl and water in an enormously greater concentrations than HCl and Na2O
     
  9. Apr 20, 2009 #8
    Is it TRULY HCl or is it just NaCl molecules suspended in water due to dissolving?

    I always thought there had to be some kind of catalytic action to cause molecules (in this case NaCl and H2O to break apart and combine with different atoms (in this case, HCl and NaOH) forming different molecular compounds. In the absence of that catalyst (be it heat, cold, pressure, whatever), it is nothing more than dissolved salt in water.

    That last two answers were exactly what I am looking for, just need some additional information. Thanks again.
     
  10. Apr 20, 2009 #9

    Borek

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    There is no such thing as NaCl molecule. Perhaps in gaseous phase, but solid NaCl is an ionic crystal, where there are no molecules.

    "Catalytic action" speeds up the reaction, but in general it doesn't change the outcome. Reactions proceed with and/or without catalysts, just much slower. That's not necesarilly true in the case of biochemical processes.

    Presence of water is enough to "break apart" both NaCl crystal structure and water molecules. In both cases you end with ions flowing in the water, surrounded by water molecules. NaCl dissociates completely, H2O only in a tiny amount.

    Now, if you have HCl dissolved, it is fully dissociated - H+ and Cl- (surrounded by water molecules) freely moving in the solution.

    Same about NaCl (Na+ and Cl-).

    Water always contain some tiny amount of H+ and OH- from the autodissociation.

    You will never understand the problem on the level of NaOH + HCl = H2O + NaCl rection equation, as it is not describing things that are really important in this case (that is, H+ + OH- <-> H2O reaction).
     
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