Understanding dissociation constants


by sodium.dioxid
Tags: constants, dissociation
sodium.dioxid
sodium.dioxid is offline
#1
May6-12, 11:15 PM
P: 51
Ka = [H+][A-]/[HA]

Is the term "[HA]" referring to its initial concentration or its equilibrium concentration?
Phys.Org News Partner Chemistry news on Phys.org
Space-tested fluid flow concept advances infectious disease diagnoses
New, more versatile version of Geckskin: Gecko-like adhesives now useful for real world surfaces
Researcher develops novel wastewater treatment fabric
Borek
Borek is offline
#2
May7-12, 01:57 AM
Admin
Borek's Avatar
P: 22,683
All concentrations are equilibrium concentrations. Initial concentration of acid (sometimes called formal or analytical) is [HA]+[A-].
sodium.dioxid
sodium.dioxid is offline
#3
May7-12, 05:52 PM
P: 51
OK, another question: why is it necessary to have both [H+] and [A-] on the numerator? It seems like we could have done just as fine using the definition "Ka=[A-]/[HA]" or "Ka=[H+]/[HA]" instead of "Ka=[H+][A-]/[HA]". Is this conventional or am I missing something?

Borek
Borek is offline
#4
May8-12, 01:48 AM
Admin
Borek's Avatar
P: 22,683

Understanding dissociation constants


As both H+ and A- are products of the reaction changing concentration of either one shifts the equilibrium, so you need both.


Register to reply

Related Discussions
Dissociation constants of NaCl/KCl Chemistry 3
Rate Constants From Equilibrium Constants Biology, Chemistry & Other Homework 6
Understanding Equilibrium Constants With No Denominator Biology, Chemistry & Other Homework 1
Detemination of dissociation constants of weak acid Biology, Chemistry & Other Homework 3
Detemination of dissociation constants of weak acid Biology, Chemistry & Other Homework 0