What is the conjugate base of HF?


How do I determine the conjugate base of HF?

There are three definition for an acid.  The one that works here is Arrhenius:  acids are proton donors (H+).  HF has a proton to donate and when it does, all that's left is an F- (no, not the grade, a fluoride!).  Fluoride in water will seek to get the proton back that it lost.  It will even take it from water.  If you take a proton from H2O, you have OH- (hydroxide).  Donating hydoxide to water is another way of identifying a base (or causing one to form, in this case).  SO:  F- is the conjugate base of  HF.    TL;DR – Take the H out of an acid and you get its conjugate base


Actually Bronsted Lowry is the one that covers conjugate acid base pairs. Arrhenius works fine for the H ion (proton) because it is same in both Arrhenius and Bronsted Lowry. But the Arrhenius base is one that makes OH- ion in water through dissociation as its definition. Bronsted Lowry definition is 'proton acceptor'. So the Bronsted Lowry 'proton acceptor' definition is the reason we have conjugate acid and base pairs. Since an acid HA is a proton donor when it loses it's proton it can accept that proton back which is the reverse reaction of HA donating a proton. A- accepting a proton is the reverse reaction. Bronsted Lowry expands the defition of bases to go broader than those that dissociated in water to form hydroxide eg. KOH, Ca(OH)2 etc... And then the third category of classification of acids and bases is Lewis Acid and that expands the definition of acid to to electron acceptor and can be more broad than just an H ion.

Any reaction is which a proton trasfer takes place from one substance to another is an acid-base reaction.More specifially the proton transfer view is know as the bronsted-lowry defincation of acids and base.

In an acid-base reaction:

An Acid : donates a proton .So, any substance that gives up the proton to another substance is an acid.

A base : accepts a proton from anoother substance . Any substance that accepts a proton from another substance is a base.

In case of HF when HF reacts with H2O it will act as an Acid and donates its H+ ( hydronium ion) so, it will act as an acid , lets look here :


HF    +   H2O <----->    F-  +    H3O +

Since HF has donated a proton HF is an acid , H20 has accepted a proton so water is a base .F- can accept a proton so F- is a base but we will call it conjugate base of HF beacuse it is generated by removing a proton from the acid HF so it is the conjugate base to the acid HF and similary , the H2O has accepted the proton so it is a base and H3O+ is the conjugate acid to the base H2O since it is generated when the H2O accpeted the proton and H3O+ can now donate the proton so it is an acid.

So, conjugate base to acid HF is F-.

I hope this make sense to you now.

F- is the conjugate base of HF, because HF is an acid. The conjugate base of an acid is formed when the acid donates a proton. 

For further clarification log on to website worldofchemicals.