Acid/Base - Water

[Snorlax]

So there's a question in my chem book that asks:
Write an equation to show each of the following acting as an acid and base with water.
a) H₂O.

Could someone enlighten me on why the answer isn't just 2 H₂O molecules?
Why/How does it become H₃O + OH

[lzxnl]

So there's a question in my chem book that asks:
Write an equation to show each of the following acting as an acid and base with water.
a) H₂O.

Could someone enlighten me on why the answer isn't just 2 H₂O molecules?
Why/How does it become H₃O + OH

H⁺ does not exist on its own in water. We're talking of a tiny positive charge which would be attracted to any negative charge it can find, and that negative charge is the negative oxygen in water. That's why we have H₃O⁺ as the acid, not H⁺

[Snorlax]

H⁺ does not exist on its own in water. We're talking of a tiny positive charge which would be attracted to any negative charge it can find, and that negative charge is the negative oxygen in water. That's why we have H₃O⁺ as the acid, not H⁺

Not sure I still understand.
The only way I can think of an answer to a question that asks H₂O + H₂O = ??  is by the fact it would create 2 molecules of water.

I guess if it says the water must be an acid, and other water molecule must be a base, then yes, I would probably write  H3O + OH, but if i were in a lab, joining 2 water molecules together, would it result in a hydronium ion and hydroxide?

[Limista]

Not sure I still understand.
The only way I can think of an answer to a question that asks H₂O + H₂O = ??  is by the fact it would create 2 molecules of water.

I guess if it says the water must be an acid, and other water molecule must be a base, then yes, I would probably write  H3O + OH, but if i were in a lab, joining 2 water molecules together, would it result in a hydronium ion and hydroxide?

Yup, but because the self-ionisation of water is an equilibrium reaction, you'd simultaneously be producing 2 water molecules in the reverse reaction anyway.

So your equilibrium mixture would consist of H2O molecules, H3O+ ions and OH- ions

That's why we have H₃O⁺ as the acid, not H⁺

Isn't H3O+ the same as H+?

[lzxnl]

Yup, but because the self-ionisation of water is an equilibrium reaction, you'd simultaneously be producing 2 water molecules in the reverse reaction anyway.

So your equilibrium mixture would consist of H2O molecules, H3O+ ions and OH- ions

Isn't H3O+ the same as H+?

Concentrated/effectively pure sulfuric acid does not contain of H⁺ and OH^-. It has H₃SO₄⁺ and HSO₄^- instead as the acid and base.
Similarly, glacial/pure ethanoic acid contains some CH₃COO^- and CH₃COOH₂⁺. Pure hydrofluoric acid also has some H₂F⁺ and FHF^-

I think my point is clear.

Not sure I still understand.
The only way I can think of an answer to a question that asks H₂O + H₂O = ??  is by the fact it would create 2 molecules of water.

I guess if it says the water must be an acid, and other water molecule must be a base, then yes, I would probably write  H3O + OH, but if i were in a lab, joining 2 water molecules together, would it result in a hydronium ion and hydroxide?

You don't have an = sign. It's a double arrow because water plus water only rarely forms hydronium and hydroxide. When a reaction does occur, hydronium and hydroxide are the result.