What makes an oxide neutral?

An oxide is neutral when it neither exhibits acidic nor basic properties, typically when the oxidation state of the element is at its highest.

In more detail, an oxide is a chemical compound that contains at least one oxygen atom and one other element. Most of the Earth's crust consists of solid oxides, the result of elements being oxidised by the oxygen in the air. Oxides can be categorised as acidic, basic, amphoteric or neutral based on their behaviour in water or in reaction with acids or bases.

Neutral oxides are a class of oxides that do not exhibit either acidic or basic properties. This means they do not react with acids to form salts nor do they react with bases to form salts. They are essentially unreactive with other acids and bases, and they do not dissociate in water to form H+ or OH- ions. Examples of neutral oxides include nitrous oxide (N2O), nitric oxide (NO), and carbon monoxide (CO).

The neutrality of an oxide is often related to the oxidation state of the element. When the element is in its highest oxidation state, the oxide is usually neutral. For instance, carbon monoxide (CO) is a neutral oxide because carbon is in its highest oxidation state (+2). Similarly, nitric oxide (NO) is neutral because nitrogen is in its highest oxidation state (+5).

However, it's important to note that not all elements in their highest oxidation states form neutral oxides. Some elements, like sulfur in sulfur dioxide (SO2), form acidic oxides even when they are in their highest oxidation states. Therefore, while the oxidation state can give us a clue about the acidity or basicity of an oxide, it is not a definitive rule.