March 28, 2024, 10:49:16 AM
Forum Rules: Read This Before Posting


Topic: acid/ base formulas  (Read 2100 times)

0 Members and 1 Guest are viewing this topic.

Offline Gammagirl

  • Regular Member
  • ***
  • Posts: 18
  • Mole Snacks: +1/-1
acid/ base formulas
« on: March 23, 2018, 04:41:13 AM »
What are the criteria for using,
ph=7-1/2(pKb +log C)
ph=1/2(pKa + log c)

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: acid/ base formulas
« Reply #1 on: March 23, 2018, 08:05:05 AM »
The formula is based on approximations, so first step is to check whether they hold.

http://www.chembuddy.com/?left=pH-calculation&right=pH-weak-acid-base
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: acid/ base formulas
« Reply #2 on: March 23, 2018, 07:30:42 PM »
Derivation of the [itex][H^+] = \sqrt{K_aC_a}[/itex] formula requires some simplifying assumptions - if they are not meet, you can't use the formula.

Whether it is better to calculate [H+] of [OH-] depends on the data you have, as long as the assumptions are meet you can use the formula that better fits the data you have, they are in many ways equivalent.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: acid/ base formulas
« Reply #3 on: March 24, 2018, 08:01:29 AM »
They are described on the page I linked to, have you tried to read it?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links