# What is the reaction mechanism between a basic oxide and an acid?

For instance in $$\ce{ Li2O (s) + 2HCl (aq) -> 2LiCl (aq) + H2O (l)}$$ I am wondering why the $\ce{Cl}$ displaces $\ce{Li}$ .I figure that oxygen is negatively charged as it pulls the electron from Lithium toward it, and that Chlorine is attracted to the lithium since chlorine is negatively charged, as itself has higher electronegativity than Hydrogen. But why dont lithium and oxygen just stick together, and hydrogen and chlorine stick together as well, instead of swapping places? Maybe it is related to the electronegativities of oxygen and lithium?

## 1 Answer

It's because the oxide ion is unstable in aqueous solutions. You may know that the dissolution of $\ce{H2O}$ into $\ce{H+}$ and $\ce{OH-}$ has a $K_w = 10^{-7}$. Trying to pull one proton off a water molecule is hard enough, pulling another one, well you get the idea.

What basically happens is that once you drop the lithium oxide into $\ce{HCl}$ solution, it dissociates into $\ce{Li+}$ and $\ce{O^{2-}}$,

$$\ce{Li2O -> 2Li+ + O^{2-}}$$

The oxide quickly grabs two protons from the acid solution.

$$\ce{O^2- +2H+ -> H2O}$$

What's left is the $\ce{Li^2+}$ and $\ce{Cl-}$ ions. They simply exist in the aqueous medium as a dissolved ionized salt.

• Thank you for your answer. I was wondering why Li2O dissociates in water? – Mr.Confused Apr 6 '18 at 14:15