How do you get pH and pOH given pka or pkb?

If you are given pKa use the Henderson-Hasselbalch equation to find pH:

pH = pKa + log(conc. of base / conc. of acid)

To convert pKb to pKa or vice versa use the following equation:

pKa x pKb = 1 x 10^-14

And use this equation to convert between pH and pOH:

pH + pOH = 14
Given pKa or pKb you can get Ka and Kb not pH or pOH.

For example pKa (HF)= 3.17

To get Ka = 10^- 3.17 =0.000671

If you want to get pH you have to know initial concentration HF.
We suppose = 0.1 M

HF <> H+ + F-

let x= moles/l HF that dissolve at equilibrium

Concentration HF = 0.1 - x
Concentration H+ = Concentration F- = x

Ka = 6.71 10 ^-4 = (x)(x) /0.1-x

x = 0.00819 M

pH = - log 0.00819 = 2.09

The answer of sureshma is valid ONLY for buffer solutions
who cares
It is very easy with the following formula.

log Ka = log [H+] + log [A--]/[HA]


HA --------> H+ + A—
(Weak Acid) (proton) (conjugate Base)
Ka (acid dissociation constant) = [H+]* [A--]/[HA]
log Ka = log [H+] + log [A--]/[HA]
--log [H+] = --log Ka + log [A--]/[HA]
pH = pKa + log [conjugate base]/[acid]
Henderson Hasselbach equation
pH = -log[H+] and pKa = --log Ka
When [A-]= [HA]
pH = pKa + log [HA]/[HA] or pH = pKa + log 1
So pH = pKa
if the concentration of the conjugate base and your weak acid are equal, than your pKa is you pH and visversa

The answers post by the user, for information only, does not guarantee the right.

More Questions and Answers:
  • The compound formed as a result of oxidation of ethyl benezene by KMnO4 is?
  • Which of the following are true for the Crystal Field Model of an octahedral complex ion? Consider ions to be?
  • Chemistry Questions?
  • One of the half-reactions for the electrolysis of water is given below.?
  • What are the various CHALLENGES facing hydrogen fuel cell technology??
  • Super hard impossible pH question...?
  • If you mix table salt with water what is the solvent and which is the solute?
  • Atomic no. of this element is 50?