aqueous cation H₃O⁺, the type of oxonium ion produced by protonation of water
Factsheet
oxonium
Other names
hydronium ion
oxonium
Other names
hydronium ion
Since your solvent is itself water, it makes no difference whether you use 
or 
.
is basically the hydrated form of 
. If you know, the oxygen atom in water contains two lone pairs. When it donates one of the lone pairs to the hydrogen atom which doesn't have any electrons, you get 
.
So,
is not 
is 
This means that the aqueous form of 
is represented as 
In all cases, acids yield protons ( or hydronium ions H3O+) and bases yield OH- (hydroxide) ions in aqueous solutions.
The H3O+ ion is considered to be the same as the H+ ion as it is the H+ ion joined to a water molecule. The proton cannot exist in aqueous solution, due to its positive charge it is attracted to the electrons on water molecules and the symbol H3O+ is used to represent this transfer.
The equation can be written as:
H+ + H2O(l) → H3O+(aq).
This is hydrolysis as it is involving water as a reactant.
Consider the first equation in the question , the ionisation equation of water:
H2O(l) + H2O(l)→H3O+(aq) + OH-(aq)
The H3O+ is the conjugate acid of H2O. So H3O+ is used as a shorthand for a proton in aqueous solution. In a non-aqueous solution the proton would form a different structure.
The second equation:
H2O(l) → H+(aq) + OH-(aq)
Shows that H2O is made up of equal parts H+ and OH- ions and is amphoteric (can be an acid or a base) having a deprotonated form (OH-). The ionic component is at a very low concentration and a water molecule is generally considered covalent with a dipole moment favouring a slight positive charge.
The H3O+ ion concentration in pure water at 25° C is 10^-7 dm^-3. This can be written as:
[H3O+] = 10^-7
where the symbol [ ] means the "molarity of" (units in moles dm^-3).
The number of H3O+ and OH- ions formed by the ionisation of pure water must be equal ( from the equation):
[H3O+] = [OH-] = 10^-7).
This shows that pure water is neither acidic or basic, it is neutral. The product of [H3O+] = [OH-] is the ionic product of water.
[H3O+][OH-]=10^-7 × 10^-7 = 10^-14
shows that in aqueous (water) solutions, whether acidic, basic or neutral, the product of the ion concentrations equals 10^-14.
Acidic solutions contain more H3O+ ions than OH- ions. For basic solutions it is the reverse.
Therefore a water solution is : Neutral when [H3O+]= 10^-7. Acidic when [H3O+] > 10^-7. Basic when [H3O+] < 10^-7.
Videos
I have been reading chemistry books and learned about +\- cations and anions and it got me thinking about water or H2O and I realized by using a positive charged oxygen you would have to bond 3 hydrogen to get 8 electrons. I looked into it and it is called hydronium but I saw its made from (H+)+H2O is it the same chemical? Also how does one H+ make the oxygen positive? I get they can bond because the H+ has zero electrons but how is the charge transferred? Thanks I was just curious.
Hello! What exactly are hydronium ions? I've used them in an activity as a reagent for a proposed reaction mechanism but I'm not sure if it's correct or if I should've used an acid (HCl, HBr, H2SO4) instead as a reagent. Can someone please elaborate? Thanks!
If this matters: I think the reaction we're trying to show is supposed to be electrophilic addition showing hydride shift.