posted by .

how do you find the pH of a titration solution at its halfway point to the equivalence, and how would it affect solutions dealing with strong acids and strong bases, this is an example just to see it quantitatively:
100.0 mL of 0.100 M HF (Ka = 7.2 x 10-4) by 0.100 M NaOH

  • Chemistry -

    The pH at the halfway point of a weak acid/srong base or weak base/strong acid is pH = pKa.
    Look at the Ka expression for a weak acid.
    Ka = (H^+)(A^-)/(HA).
    Now solve this for H^+.
    (H^+) = Ka*[(HA)/(A^-)].
    When you are halfway there, the (HA) = (A^-); therefore, Ka = (H^+). If you take the -log of both sides we get
    -logKa = -log(H^+).
    By definition the left side is pKa and the right side is pH.
    For the titration of a strong acid/strong base, there is no Ka and this rules doesn't apply.
    For your example,
    millimoles HF = 100 mL x 0.1 = 10 mmols initially.
    Halfway there is 50 mL NaOH x 0.1 = 5 mmols.
    So you have 5 mmols of the salt formed (NaF) and you have 10.0-5.0 = 5.0 millimols HF remaining. Plug those into the equation I had above and you see one is in the numerator and one in the denominator so they cancel and (H^+) = Ka.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemisty

    In titrations of acids and bases, what is the difference between the end point of the titration, and the equivalance point?
  2. chemistry

    ) At the equivalence point in the titration of a strong acid with a strong base, do you expect the pH to be acidic, basic, neutral?
  3. AP Chemistry

    Assume that 30.0 mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of a monoprotic strong acid HX. (a) How many moles of HX have been added at the equivalence point?
  4. chemistry

    if 0.4M NaOH is titrated with 0.4M HF, how do we calcualte the ph at equivalence. The book assumes each is 1L, but why do we use 1L * chemistry - Dr.Jim, Thursday, November 11, 2010 at 5:31am HF is a weak acid, so you need the dissociation …
  5. Chemistry

    A concept map was to be created on acids and bases. The concept terms that were given to use were: aqueous solution,bases,acids,ions,weak bases, strong bases, strong acids, weak acids,dissociation, weak electrolyte, strong electrolyte,reaction,salt, …
  6. chemistry

    There is a titration of 5.00 mL .010 M NaOH with .005 M HCl. Indicate the pH of the initial and final solutions and the pH at the stoichiometric point. What volume of HCl has been added at the stoichiometric point and the halfway point …
  7. Chemistry

    HOBr (aq) <----> H+ (aq) + OBr- (aq), Ka = 2.3 x 10^-9 Hypobromous acid, HOBr, is a weak acid that dissociates in water, as represented by the equation. (a) Calculate the value of [H+] in a solution of HOBr that has a pH of 4.95. …
  8. Chemistry

    Hi everyone, I have been trying to figure out this titration equation all day and for some reason I am stumped. Here is the question in full: Potassium hydrogen phthalate, KHP, can be obtained in high purity and is used to determine …
  9. Chemistry - Acids/Bases

    What kinds of compounds are typically strong bases?
  10. Chemistry - Acid and Bases

    In aqueous solution, classify these compounds as strong acids, weak acids, strong bases, weak bases, or other. HNO3 HBr HF CH3COOH H3PO4 NaOH Ba(OH)2 (CH3)3N NH3 NaCl

More Similar Questions