Difference between H+ and H3O+

[horizon]

Hi there,

Is there any difference at ALL between the H+ ion and the hydrodium ion, H3O+?
Why do I see the H3O+ used more? Like in acid and base reactions etc...

Thank you

[REBORN]

H+ becomes H30+ when placed in water. H+ on its own is just a proton.

[Aurelian]

Almost always, H+ is simply neater notation to use, and actually represents H30+

In acid/base chemistry, H30+ is often use moreso because it more faithfully represents dissociation equations.

Thus, you might see the same acid/base reaction written two different ways;
1. HCl (aq) ---> H+ (aq) + Cl- (aq)
2. HCl (aq) + H20 (l) ---> H30+ (aq) + Cl- (aq)

For all intents and purposes, equation 1 will suffice, but equation 2 is more 'correct' with respect to what's actually going on.

However, in other areas, such as electrochemistry, where you can get quite messy redox equations, H+ is preferred for simplicity's sake.

[pi]

H+ becomes H30+ when placed in water. H+ on its own is just a proton.

Are you sure this is entirely correct? I don't think you can just add protons to water by itself...

[REBORN]

I stand corrected then. I always thought H+ was just a proton and when added to water gives H30+

[dc302]

H+ IS just a proton...but what's the question here? Yes, you don't add 'just a proton' to water but since when did we ever have to do that? o_O

[Aurelian]

Are you sure this is entirely correct? I don't think you can just add protons to water by itself...

H+ IS just a proton...but what's the question here? Yes, you don't add 'just a proton' to water but since when did we ever have to do that? o_O

When acids dissociate, under the Bronsted-Lowry definition of an acid, the acid will donate a proton to the solution; this proton then 'reacts' with water molecules to make hydronium ions.

Moderator action: removed real name, sorry for the inconvenience

[horizon]

Thanks guys!
Just want to clarify this since I'm a bit confused with the different opinions:

H+ becomes H30+ when placed in water. H+ on its own is just a proton.

Is this true?

[Hellrocks]

The H becomes H3O+ when reacted with water, not the H+.

E.g. H2O + H-Cl => H3O+ + Cl-

So the oxygen on in the H2O grabs the H in the H-Cl, the H bonded to the Cl is not existing as a H+. Although it is an acidic hydrogen.

[Hamdog17]

You can add H+ in the form of a pure acid like HCl bubbled through water. The acid will dissociate with water to form hydronium H+ + H2O <-----> H3O+ as shown. This reaction is reversible and is very rapid occurring thousands of times a second. The H+ although technically present isn't really there for very long.

[Hellrocks]

In solution the bare hydrogen ion doesn't exist, and there is no driving force to make that process of dissociation occur if H2O was not to take part in the reaction.

[VivaTequila]

A H+ ion is a H+ ion. I'd imagine you'd only find this in nuclear physics.

ssNake was 100% correct for the reasons that Aurelian mentioned - Redox reactions use H+ to avoid equations getting messy.

A H3O+ molecule exists. It is not a lone proton. Therefore it is different to H+.

For VCE 3/4 Chemistry's sake you can prescriptively say that the H+ ion is simply shorthand for H3O+ when in reality they are completely different.

Edit: To clarify, all that is used in 3/4 Chemistry is H3O+. In Redox reactions, including H3O+ can become quite complicated. For the sake of simplicity, H+ can substituted to simplify the chemical expression. It can also be substituted in acid/base reactions because for simplicity's sake as well, but it should really be kept to H3O+.

A H+ ion undoubtedly exists, but it would be incredibly reactive and I'd imagine only come about in the realms of nuclear physics. Not VCE 3/4 Chemistry.

[dc302]

You guys are over complicating things: you DON'T just 'randomly' interchange H+ and H3O+

Why is it that sometimes you see H+ in an equation, and H3O+ in others? H+ is when you have an ionic equation in general, H3O+ is used for full equations in general. Sometimes you may see both in the same equation but that's different.

ionic equation: HCl (aq) ---> H+ (aq) + Cl- (aq)
full equation: HCl (aq) + H20 (l) ---> H30+ (aq) + Cl- (aq)
other case: H2O + H+ <--> H3O+ (altho you will hardly see these so it doesn't matter).

Now what's the OTHER case where you may see H+ and H3O+ interchange? When you are talking about CONCENTRATION.

[H+] = [H3O+] is commonly assumed, so this is why you may see it interchanged. H+ and H3O+ are not the same, and they are not randomly interchanged for convenience sake either, except in the case of concentration. Feel free to add if I have left cases out.

[Mao]

other case: H2O + H+ <--> H3O+ (altho you will hardly see these so it doesn't matter).

This does not happen. H+ and H2O cannot coexist due to the vast difference between their internal energy.

[dc302]

other case: H2O + H+ <--> H3O+ (altho you will hardly see these so it doesn't matter).

This does not happen. H+ and H2O cannot coexist due to the vast difference between their internal energy.

Sorry, take away the reverse sign.

H2O + H+ --> H3O+