Page 2 of 2 FirstFirst 12
Results 16 to 18 of 18

Math Help - pKa and pKb calculation

  1. #16
    Newbie
    Joined
    Jan 2008
    From
    Surrey - home / Portsmouth - uni
    Posts
    20
    rightyo I tried to put in values for the equation but I have no idea what goes where ... Don't worry I'll just make up the marks on the organic chemistry bit lol I give up on this stuff
    Follow Math Help Forum on Facebook and Google+

  2. #17
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by Dan167 View Post
    rightyo I tried to put in values for the equation but I have no idea what goes where ... Don't worry I'll just make up the marks on the organic chemistry bit lol I give up on this stuff
    i don't see your hang up, Dan.

    you have x^2 + K_ax - 0.1K_a = 0 there are not many choices of where to put anything. you know that K_a = 3.3 \times 10^{-2}, so just replace K_a with that wherever you see it, so you get

    x^2 + {\color{red}(3.3 \times 10^{-2})}x - 0.1{\color{red}(3.3 \times 10^{-2})} = 0

    so you get x^2 + 0.033x - 0.0033 = 0

    so here your a = 1, your b = 0.033 and your c = -0.0033

    so, x = \frac {-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac {-0.033 \pm \sqrt{(0.033)^2 - 4(1)(0.0033)}}{2}

    and just plug that in your calculator

    when you get the answer, take the logarithm of it and then take it's negative and you have the pH
    Follow Math Help Forum on Facebook and Google+

  3. #18
    Super Member
    Joined
    Oct 2007
    From
    London / Cambridge
    Posts
    591
    If your having difficulty with the qudratic formula just assume that the change in conceration of the acid can be nelgated and use the following formula instead.

    Ka = \frac{x^2}{[Acid]}

    your answer will be a bit off, but your chemistry teachers may not mind, you should ask them is that is allowed on your course (because it is on mine).

    Yeah we have the same general feeling in my chemistry class as well most people make up all the marks on the organic chemistry, I however make up the marks with analytical chemistry .
    Follow Math Help Forum on Facebook and Google+

Page 2 of 2 FirstFirst 12

Similar Math Help Forum Discussions

  1. Help with calculation...
    Posted in the Algebra Forum
    Replies: 1
    Last Post: December 7th 2011, 04:55 AM
  2. Need help with a calculation
    Posted in the Algebra Forum
    Replies: 9
    Last Post: January 8th 2011, 12:02 PM
  3. GDP calculation
    Posted in the Business Math Forum
    Replies: 0
    Last Post: December 1st 2010, 10:33 AM
  4. SST Calculation
    Posted in the Advanced Statistics Forum
    Replies: 4
    Last Post: October 21st 2010, 01:58 PM
  5. Age calculation
    Posted in the Algebra Forum
    Replies: 5
    Last Post: April 8th 2008, 11:27 PM

Search Tags


/mathhelpforum @mathhelpforum