MadSci Network: Chemistry

Re: Explain how proton balance controls pH.

Date: Fri Mar 6 15:57:04 1998
Posted By: Uncle Al Schwartz, Organic synthetic chemist
Area of science: Chemistry
ID: 888733223.Ch

The "educator?"  Do you know the story "The Emperor's New Clothes?"

Assuming unit chemical activities (dilute solution), pH is the negative
common logarithm of the hydrogen ion concentration (the "p" means "negative
common logarithm of").  There is neither mystery nor romance to it.  It is
merely a concentration of a species in solution.

  1a) You look up the pKa of HOCl.  You now know the Ka.
      You write the hydrolysis equation OCl- + H20 <--> HOCl + OH-
      You write the equilibrium expression from the equation
      You plug in the known concentrations and the HOCl ionization 
      You solve for the unknown [H+] (or [OH-]; they're related)
      You take -log[H+] to get the pH.

It is no different from figuring out the pH of an acetate buffer.          
  1b) Same idea,  You look up the disproprotionation (or 
constant of Cl2 + H2O <--> HOCl + HCl (or the equation in base; whatever).

   2) You could do something daring, going beyond cracking your textbook,
like looking it up in another text (library).  Or confront your instructor
and have it (no gender attribute - politically correct) actually teach
something - as in successfully conveying useful information.

(Ammonia is the least of your worries in millimolar solution.  Worry about
H2Se outgassing.)  Ammonia cannot outgas as the neutral molecule if it is
protonated as the ion.  Under what conditions does that obtain?

Uncle Al Schwartz ("zero" before @)
 (Toxic URLs! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?"  The Net!                                 

Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1998. All rights reserved.