Problem 22 - Chemistry and Chemical Reactivity

Question

Write balanced equations for the reaction of lithium, sodium, and potassium with \(\mathrm{O}_{2} .\) Specify which metal forms an oxide, which forms a peroxide, and which forms a superoxide.

Step-by-Step Solution

Answer

Lithium forms an oxide, sodium forms a peroxide, and potassium forms a superoxide.

Step 1: Write the Reaction for Lithium with O2

Lithium reacts with oxygen to form lithium oxide. The chemical equation for this reaction is:\[ 4\text{Li} + \text{O}_2 \rightarrow 2\text{Li}_2\text{O} \]This equation shows that lithium oxide is formed when lithium reacts with oxygen.

Step 2: Write the Reaction for Sodium with O2

Sodium reacts with oxygen to form sodium peroxide. The chemical equation for this reaction is:\[ 2\text{Na} + \text{O}_2 \rightarrow \text{Na}_2\text{O}_2 \]This equation indicates that sodium forms a peroxide with oxygen.

Step 3: Write the Reaction for Potassium with O2

Potassium reacts with oxygen to form potassium superoxide. The chemical equation for this reaction is:\[ \text{K} + \text{O}_2 \rightarrow \text{KO}_2 \]This reaction shows that potassium forms a superoxide when it reacts with oxygen.

Key Concepts

Lithium Oxide Formation

Lithium, one of the alkali metals, reacts with oxygen in a straightforward manner to form lithium oxide. In this reaction, oxygen acts as an oxidizing agent, accepting electrons from lithium. The balanced chemical equation for this process is:\[ 4\text{Li} + \text{O}_2 \rightarrow 2\text{Li}_2\text{O} \]### Understanding the Equation

• Four lithium atoms (Li) react with one molecule of oxygen (\(\text{O}_2\)).
• The product is two units of lithium oxide (\(\text{Li}_2\text{O}\)).

Lithium oxide is a simple oxide, meaning that it consists of the metal lithium combined with oxygen in a basic 2:1 ratio. This reaction is typical for lithium due to its relatively strong attraction to oxygen when compared to heavier alkali metals. The production of lithium oxide in this process exemplifies one of the fundamental properties of alkali metals, their ability to react actively with oxygen to form binary compounds.

Sodium Peroxide Formation

In the case of sodium reacting with oxygen, sodium forms a compound known as sodium peroxide. Sodium and oxygen unite to form this compound more complex than lithium oxide. Here's the balanced equation:\[ 2\text{Na} + \text{O}_2 \rightarrow \text{Na}_2\text{O}_2 \]### Key Points about Sodium Peroxide

• Two sodium atoms (\(\text{Na}\)) combine with one oxygen molecule (\(\text{O}_2\)).
• The result is sodium peroxide (\(\text{Na}_2\text{O}_2\)).

Sodium peroxide is an example of a peroxide, a structure where each oxygen atom is singly bonded with another oxygen atom. This formation represents a shift from simpler oxides to compounds that involve more complex oxygen bonding. Sodium's peroxide formation is indicative of its moderate reactivity level within the alkali metals, residing between the simple oxides of lithium and the highly reactive compounds formed by heavier alkali metals.

Potassium Superoxide Formation

Potassium exhibits even more interesting chemistry by forming a superoxide with oxygen. This reaction is described by the equation:\[ \text{K} + \text{O}_2 \rightarrow \text{KO}_2 \]### Characteristics of Potassium Superoxide

• Each potassium atom (K) reacts with one molecule of oxygen (\(\text{O}_2\)).
• The product is potassium superoxide (\(\text{KO}_2\)).

A superoxide contains a unique O₂^- ion, which sets them apart from oxides and peroxides. Potassium superoxide is highly reactive and is used in applications like respiratory devices where it provides oxygen upon decomposition. The formation of a superoxide instead of a simple oxide or peroxide highlights potassium's position among alkali metals as highly reactive, comparable with heavier counterparts like rubidium and cesium. This superoxide formation showcases potassium's unique capability to stabilize this unusual oxygen species.