What is the Ionic equation for a metal oxide reaction with acid?

Some reactions of the type need to go to an ionic state before the reaction can be written.

Na2O + 2HCl→ 2NaCl + H2O is hard to resolve in ionic terms, but

Na2O + H2O → 2NaOH can be presented as Na2O(s) + H2O (l) → 2Na+ (aq)+ 2OH- (aq) and the rest done conventionally:

2Na+(aq) + 2OH-(aq) + 2H+(aq) + 2Cl-(aq) → 2Na+(aq) + 2Cl-(aq) + 2H2O(l)

With only the autoionization to about 10^-14 molar, the overall effect is the surprising formation of liquid water, the “precipitate” in this irreversible ionic reaction. This is the net ionic equation.

All metal oxides are basic and as such an acid-base neutralisation reaction takes place with Base + Acid -> Salt + Water.

Take Magnesium oxide (MgO) and Hydrochloric acid (HCl).

The overall reaction is MgO + 2HCl -> MgCl2 + H2O.

But the definition of an iconic equation makes it so that only the ions that are changing are shown so let's write this equation again but with the charges of ions shown in brackets.

Mg(2+)O(2-) + 2H(1+)Cl(1-) -> Mg(2+)Cl2(2-) + H2O(0)

• Magnesium stays constant at 2+
• Cl stays constant at 1- for each ion (there are 2)
• Oxygen (2-) is oxidsed to Oxygen (O)
• Hydrogen (1+) is reduced to H2(0)

So the overall ionic equation for this an incidentally any metal oxide and acid is:

2H(+) + O(2-) -> H2O

For a hydroxide you need one less mole of acid as you gain a H from the hydroxide so those equations look like:

H(+) + OH(-) -> H2O