Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculate the pH of concentrated hydrochloric acid

  1. Nov 1, 2008 #1

    a.a

    User Avatar

    1. The problem statement, all variables and given/known data

    Calculate the pH of concentrated hydrochloric acid if this solution is 24.8 % HCl by weight and has a density of 1.16 g/mL.

    2. Relevant equations



    3. The attempt at a solution
    \the percentage is throwing me of, can someone explain what it is?
     
  2. jcsd
  3. Nov 1, 2008 #2
    Re: pH

    I'm wildly guessing here, but if "percent by weight" somehow is supposed to mean "percent by mass," it would make things pretty easy; in 1.16g/mL, 28% of 1.16g would be HCl: (1.16g/mL)(0.28) = 0.3248g/mL.

    From there, you can do some converting to eventually get to pH; I'll assume for now that only the percentage was tripping you up.
     
  4. Nov 1, 2008 #3

    a.a

    User Avatar

    Re: pH

    hey, useing what u told me i think i mite be getting somewhere:

    n HCl = (0.248)*(1.16g)/(36.453g/mole) = 0.0789 moles

    The molar concentration is thus [HCl] = (0.00789 moles)/(0.001 lit)

    = 7.89M = [H+]

    pH = -log([H+]) = -0.897

    can someone verify?
     
  5. Nov 1, 2008 #4

    Borek

    User Avatar

    Staff: Mentor

    Re: pH

    Yes and no. Yes - you did your best and that's probably what your teacher wants. No - in such concentrated solutions pH can't be calculated this way. But that's not your fault and you can't do anything about it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook