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!

Calculate the pH of a solution made by dissolving 10.6 g caffeine

  1. Mar 21, 2009 #1

    a.a

    User Avatar

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

    Calculate the pH of a solution made by dissolving 10.6 g caffeine (C8H10N4O2, a weak base, Kb = 4.1 x 10-4) in enough water to make 100. mL of solution.

    2. Relevant equations
    pH = -log [H3O+]
    kb = kw/ka


    3. The attempt at a solution

    I first found conc.:
    MM= 194.2
    m = 10.6
    n = 0.05458 mol
    conc. = 0.5458

    kb = (10^-14)/ (4.1 x 10-4)
    = 2.439*10^11

    kb= x^2 / 0.5458
    ... x = 3.64 *10^-6
    pOH = -log pOH
    pH = 14 - pOH
    = 8.56

    But this is wrong... where did I go wrong?
     
  2. jcsd
  3. Mar 22, 2009 #2

    Borek

    User Avatar

    Staff: Mentor

    Re: pH

    You were already given Kb.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Calculate the pH of a solution made by dissolving 10.6 g caffeine
Loading...