Кислотно/основні властивості оксидів

What are Oxides?

An oxide is a molecule or compound with an oxygen atom bonded to one element. The bond can be either ionic or covalent. It depends on the electronegativity difference between oxygen and the other element. Do you remember seeing oxides before? Way back, we studied oxoanions. They're oxide ions and are typically the conjugate bases of strong acids.

Oxides as Acids

Many oxides form acids. But, which oxides are acidic? The acidic oxides form between oxygen and non-metals. For example, consider carbon dioxide, $CO_{2}$. What happens when it reacts with water? Let's write a chemical equation. $CO_{2} + H_{2}O \rightarrow H_{2}CO_{3}$. We produce carbonic acid! It's a weak polyprotic acid.

Let's consider another example. Let's react nitrogen dioxide with water. Its balanced chemical equation is $3NO_{2} + H_{2}O \rightarrow 2HNO_{3} + NO$. In this case, we've generated nitric acid. It's a strong Arrhenius acid! So, it will lower our pH significantly.

Oxides as Bases

What oxides are basic? We know the non-metal oxides are acid. So, we could reason that the metal oxides are basic. And our reasoning is correct! Specifically, the alkali and alkaline-earth metal oxides are very basic. For example, let's consider the reaction between magnesium oxide and water. Its chemical equation is $MgO + H_{2}O \rightarrow Mg^{+} + 2OH^{-}$. We produced two moles of hydroxide ions! So, our solution is basic and will have a very low pOH.

Amphoteric Oxides

Some oxides are amphoteric. They can be acidic or basic. Many of the amphoteric oxides are transition metals or group 3 metals. Let's look at tin (IV) oxide as an example.

In acidic conditions:

$SnO_{2} + HCl \rightarrow H_{2}SnCl_{4} + 2H_{2}O$

• The reaction between tin and hydrochloric acid is unique. The chlorine replaces the oxygen. At the same time, it neutralizes the hydrogen ion.

In basic conditions:

$SnO_{2} + 2NaOH \rightarrow Na_{2}SnO_{3} + H_{2}O$

• Again, the reaction is notable. The sodium adds to the tin. The reaction neutralizes the hydroxide ion.

Neutral Oxides

A handful of oxides are neutral. They do not react with either acids or bases. Generally, they are very stable covalent compounds with multiple bonds. For example, carbon monoxide and nitrogen monoxide are triple bonded. Another example is dinitrogen monoxide. It's stabilized by having two resonance structures.

(Video) 3.2 Bonding and acid-base properties of the period 3 oxides (SL)

By Mike Sugiyama Jones

In this quick video, Mike Jones explains the properties of the period three oxides. You'll see examples of acidic, basic, and amphoteric oxides. You'll also learn how their bonding affects their acid-base character. This is a great quick video for exploring oxides!

(Video) Acidic and Basic Oxides

By Chemistry Demo Lab Ohio State University

In this video, the Chemistry Demo Lab at Ohio State shows you how different oxides can be acidic or basic. They use a Yamada pH indicator. So, it's blue under basic conditions and orange under acidic conditions. You'll see a couple of ionic and covalent compounds and how they differ. This video is a fascinating demo that will help you visualize the pH of oxides.