Question

\(\mathrm{Li}_{2} \mathrm{O}_{2}\) is formed when: (a) \(\mathrm{LiOH}\) is heated in an atmosphere of \(\mathrm{O}_{2}\) (b) Li is heated strongly is excess of air. (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) and alcohol are added to a solution of \(\mathrm{LiOH}\) in water. (d) Both (a) and (c).

Short answer

Option (b) is correct: Li heated in excess air forms \( \mathrm{Li}_2 \mathrm{O}_2 \).

Step-by-step solution

Analyzing Option (a)

The reaction of lithium hydroxide \( \mathrm{LiOH} \) heated in the presence of \( \mathrm{O}_2 \) typically does not directly form \( \mathrm{Li}_2 \mathrm{O}_2 \). Heating \( \mathrm{LiOH} \) in \( \mathrm{O}_2 \) usually results in the decomposition to form lithium oxide (Li2O), not lithium peroxide \( \mathrm{Li}_2 \mathrm{O}_2 \).

Analyzing Option (b)

When lithium \( \mathrm{Li} \) is heated strongly in an excess of air, it reacts with the oxygen in the air to form lithium peroxide \( \mathrm{Li}_2 \mathrm{O}_2 \). The general reaction is \[ 2 \mathrm{Li} + \mathrm{O}_2 \rightarrow \mathrm{Li}_2\mathrm{O}_2 \]. This is a feasible condition for formation of \( \mathrm{Li}_2 \mathrm{O}_2 \).

Analyzing Option (c)

Mixing \( \mathrm{H}_2 \mathrm{O}_2 \) and alcohol with a solution of \( \mathrm{LiOH} \) in water can form \( \mathrm{Li}_2 \mathrm{O}_2 \). This is due to the reaction involving \( \mathrm{H}_2 \mathrm{O}_2 \), which can provide the necessary peroxide component to generate \( \mathrm{Li}_2 \mathrm{O}_2 \).

Conclusion on Option (d)

Evaluating both options (a) and (c), only (c) is valid for directly forming \( \mathrm{Li}_2 \mathrm{O}_2 \). However, given option (b) is correct, the answer is neither (a) nor (d) can be correct simultaneously.

Key concepts

Lithium Peroxide

Lithium Peroxide, represented chemically as \( \mathrm{Li}_2 \mathrm{O}_2 \), is an inorganic compound that consists of lithium and peroxide ions. Lithium peroxide is typically formed under specific conditions and reactions.
One common method to produce lithium peroxide is by heating lithium metal in the presence of an excess of air, or more specifically, in an atmosphere with plenty of oxygen. This reaction can be represented as:

• \( 2 \mathrm{Li} + \mathrm{O}_2 \rightarrow \mathrm{Li}_2 \mathrm{O}_2 \)

The lithium metal directly reacts with oxygen, leading to the formation of lithium peroxide. This compound is interesting due to its use in applications like oxygen generation systems, where it releases oxygen upon decomposition. Understanding the chemical properties and formation of lithium peroxide helps us utilize it effectively in industrial applications.

Lithium Hydroxide

Lithium Hydroxide, or \( \mathrm{LiOH} \), is another important lithium compound predominantly known for its role in chemical reactions. Although \( \mathrm{LiOH} \) itself doesn’t form lithium peroxide directly when heated in oxygen, it is crucial in several processes.
When \( \mathrm{LiOH} \) is exposed to heat in an oxygen-rich atmosphere, it tends to decompose, forming lithium oxide \( \mathrm{Li}_2 \mathrm{O} \) instead. This compound consists of lithium and oxide ions, and the reaction can be outlined as follows:

• \( 4 \mathrm{LiOH} \rightarrow 2 \mathrm{Li}_2 \mathrm{O} + 2 \mathrm{H}_2 \mathrm{O} \)

However, mixing \( \mathrm{LiOH} \) with hydrogen peroxide \( \mathrm{H}_2 \mathrm{O}_2 \) under aqueous conditions can lead to the formation of lithium peroxide. This highlights the versatility and adaptability of \( \mathrm{LiOH} \) in chemistry to participate in multi-step processes.

Chemical Reactions with Lithium

Lithium, a highly reactive alkali metal, participates in a multitude of chemical reactions, showcasing its reactivity and forming various compounds.
One of the hallmark reactions of lithium is its interaction with oxygen to form lithium peroxide \( \mathrm{Li}_2 \mathrm{O}_2 \). When lithium is heated in the presence of excess air, it readily combines with oxygen:

• \( 2 \mathrm{Li} + \mathrm{O}_2 \rightarrow \mathrm{Li}_2 \mathrm{O}_2 \)

Besides reacting with oxygen, lithium can react with water, acids, and other substances, illustrating its chemical versatility.
An important reaction is lithium's interaction with water, which produces \( \mathrm{LiOH} \) and hydrogen gas. This can be represented as:

• \( 2 \mathrm{Li} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{LiOH} + \mathrm{H}_2 \)

These reactions underscore lithium's capability to engage with different elements and compounds, resulting in diverse chemical formations.