1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

PH concentrations, strong acids and water

  1. Jan 22, 2010 #1
    Hello!
    I was wondering, with questions such as "What is the pH of 0.05 mol dm-3 of HCl?", you specify the pH by simply using the concentration, as it completely dissociates. However, I assume that at such a concentration like this it is not 'pure', and would be present in water. Shouldn't I then have to consider the [H+] and [OH-] concentrations of water?
    Thanks for any help.
     
  2. jcsd
  3. Jan 22, 2010 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    They are in water, that's what mol/dm3 means.
    So in every liter of solution, there is 0.05 mol of HCl. The rest is pure water, which is neutral (in the sense that the concentration of H+ and OH- is equal to great accuracy).
     
  4. Jan 22, 2010 #3
    so shouldn't the [H+] introduced be included with the [H+] of the water for an overall pH value?
    Sorry, it has not been a good day...
     
  5. Jan 23, 2010 #4

    Borek

    User Avatar

    Staff: Mentor

    If concentration of acid is high enough they can be safely ignored. High enough in this context means more than 5*10-7M.

    See calculation of pH of strong acid for more details.
     
    Last edited by a moderator: Aug 13, 2013
  6. Jan 23, 2010 #5
    Ah, many thanks Compuchip and Borek. I looked into calculating pH, and I have covered it in class, I couldn;t find it mentioned on a site, and I don't think it came up in class, although it may have done...
    Once again, many thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: PH concentrations, strong acids and water
  1. Strong acid and pH (Replies: 10)

Loading...