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Homework Help: PH of Hydroclauric acid

  1. Jul 26, 2006 #1
    I want to ask that there is any situation that the solution of Hydroclauric acid and water can make the pH of this solution gretater than 7.
  2. jcsd
  3. Jul 26, 2006 #2
    Yes, to some extent. At pH 7 there is no abundance of H+ or OH-.

    However, water has the following reaction:

    H2O -> H+ + OH-

    So strickly theoretically speaking, if the acid is very diluted, your water isn't pure and the conditions are favourable, why not?
  4. Jul 26, 2006 #3
    [tex]2H_2O \longrightarrow H_3O^+ + OH^-[/tex]

    The self-ionization of water is endothermic (see reaction above). If you low the temperature, the concentration of [tex]H_3O^+[/tex] will diminish and the pH will be greater than 7 for a pure water. If you add very dilute hydrochloric acid at this conditions it is very probable that the pH of this solution is greater than 7.
  5. Jul 28, 2006 #4
    Not really. HCl, Hydrochloric Acid can only ADD H+ ions, and LOWER the pH.
    If you really want to nit pick, however...
    At temperatures below 25 degrees C, the pH of pure water is slightly higher than 7.0. At 15 C, it's about 7.16, for example. So if you take cold water, and any such a tiny amount of HCL that it won't lower the pH below 7.0, you can have an HCL solution with a pH above 7.00. (But adding the HCl still lowered the pH a bit).
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