What are some of the equilibrium expressions that chemists use for weak acid equilibrium?
Chemistry - DrBob222, Saturday, March 30, 2013 at 11:21pm
Ka = (products)/(reactants)
with coefficients becoming exponents.
Chemistry - Anonymous, Saturday, March 30, 2013 at 11:27pm
Are there any more expressions for weak acids equilibrium? It would be helpful in the long run to know what they all are if there are any more.
Chemistry - DrBob222, Sunday, March 31, 2013 at 12:14am
You're question is so general that I didn't know what to write the first time and certainly I don't know what to write now. For a weak acid, such as HA, it ionizes as
HA(aq) + H2O(l) ==> H3O^+(aq) + A^-(aq) in which aq stands for aqueous (as in solution) and l stands for liquid (meaning pure H2O), the
Ka = (H3O^+)(A^-)/(HA)
All follow that same generic Ka. There are some diprotic and triprotic acids but they follow the same rules. For example, H2CO3 is
H2CO3(aq) + H2O(l) ==>H3O^+(aq) + HCO3^-(aq) and k1 for that ionization is
k1 = (H3O^+)(HCO3^-)/(H2CO3)
The second hydrogen then ionizes as
HCO3^-(aq) + H2O(l) ==>H3O^+(aq) + CO3^2-(aq) for which k2 is
k2 = (H3O^+)(CO3^2-)/(HCO3^-)
H3PO4, a triprotic acid, works the same way and it has a k1, a k2, and a k3 in which one H comes off at a time.
If you have a specific problem it would be easier to answer that than trying to stay with general cases.