Question

(a) Suggest products for the reaction of \(\mathrm{Li}_{3} \mathrm{N}\) with water. Write a balanced equation for the reaction. (b) \(\mathrm{A}\) compound \(\mathbf{A}\) was isolated from the reaction between a group 1 metal \(\mathrm{M}\) and \(\mathrm{O}_{2} .\) A reacts with water to give only MOH, while M reacts in a controlled manner with water giving \(\mathrm{MOH}\) and another product, B. Suggest identities for \(\mathrm{M}, \mathrm{A}\) and \(\mathrm{B}\). Write equations for the reactions described. Compare the reaction of \(\mathrm{M}\) with \(\mathrm{O}_{2}\) with those of the other group 1 metals with \(\mathrm{O}_{2}\)

Short answer

For (a), the products are \( \mathrm{3LiOH} \) and \( \mathrm{NH}_3 \). For (b), \( \mathrm{M} \) is lithium, \( \mathrm{A} \) is \( \mathrm{Li}_2\mathrm{O}_2 \), and \( \mathrm{B} \) is \( \mathrm{H}_2 \).

Step-by-step solution

Understand the Reaction in Part (a)

Lithium nitride \( \mathrm{Li}_3\mathrm{N} \) reacts with water to produce ammonia (\( \mathrm{NH}_3 \)) and lithium hydroxide (\( \mathrm{LiOH} \)). This is because lithium nitride reacts with water to form ammonia gas and a metal hydroxide.

Write the Balanced Equation for Part (a)

The balanced chemical equation for the reaction of lithium nitride with water is:\[ \mathrm{Li}_3\mathrm{N} + 3\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{3LiOH} + \mathrm{NH}_3} \]

Identify Compound A in Part (b)

Compound \( \mathbf{A} \) is a peroxide because it results from the controlled reaction of a group 1 metal with \( \mathrm{O}_2 \) that reacts with water to form a single hydroxide. For lithium, \( \mathbf{A} \) is \( \mathrm{Li}_2\mathrm{O}_2 \), lithium peroxide.

Determine the Metal M in Part (b)

The metal \( \mathrm{M} \) is lithium \( \mathrm{Li} \). This is because lithium forms \( \mathrm{LiOH} \) and hydrogen gas \( \mathrm{H}_2 \) when it reacts with water, and forms \( \mathrm{Li}_2\mathrm{O}_2 \) when it reacts with \( \mathrm{O}_2 \).

Identify Product B in Part (b)

Product \( \mathrm{B} \) is hydrogen gas \( \mathrm{H}_2 \), which is released when \( \mathrm{Li} \) reacts with water in a controlled manner.

Write Equations for Reactions in Part (b)

1. Controlled reaction of \( \mathrm{Li} \) with water: \( 2\mathrm{Li} + 2\mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{LiOH} + \mathrm{H}_2 \) 2. Reaction of \( \mathrm{Li} \) with \( \mathrm{O}_2 \) to form \( \mathrm{Li}_2\mathrm{O}_2 \): \( 2\mathrm{Li} + \mathrm{O}_2 \rightarrow \mathrm{Li}_2\mathrm{O}_2 \)3. Reaction of \( \mathrm{Li}_2\mathrm{O}_2 \) with water: \( \mathrm{Li}_2\mathrm{O}_2 + 2\mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{LiOH} + \mathrm{H}_2\mathrm{O}_2 \)

Compare Reactions with Other Group 1 Metals

Lithium reacts with \( \mathrm{O}_2 \) to form a peroxide (\( \mathrm{Li}_2\mathrm{O}_2 \)), while other group 1 metals like sodium and potassium react to form superoxides or peroxides, such as \( \mathrm{Na}_2\mathrm{O}_2 \) and \( \mathrm{KO}_2 \), respectively. The nature of the product differs due to the size and ionization energy of the metals.

Key concepts

Lithium Nitride Reactions

Lithium nitride (\( \mathrm{Li}_3\mathrm{N} \)) is a fascinating compound, especially when it reacts with water. This reaction is notable for its ability to produce two distinct substances: ammonia \( (\mathrm{NH}_3) \) and lithium hydroxide \( (\mathrm{LiOH}) \). To understand this better, let's go through it step by step.
When \( \mathrm{Li}_3\mathrm{N} \) is added to water, it breaks down in such a way that the nitrogen atom forms ammonia gas while the lithium atoms form lithium hydroxide. Here is the balanced chemical equation for this process:

• \( \mathrm{Li}_3\mathrm{N} + 3\mathrm{H}_2\mathrm{O} \rightarrow 3\mathrm{LiOH} + \mathrm{NH}_3 \)

The beauty of this reaction lies in its simplicity and the straightforward formation of products.Understanding and predicting such reactions provides insight into the chemistry of alkali metal nitrides, and the production of ammonia serves as a classic example of inorganic synthesis.

Peroxides and Superoxides

Peroxides and superoxides are unique forms of oxygen compounds that differ in their structure and reactivity. This difference primarily hinges on the number of oxygen atoms and their coupling with alkali metals.
For lithium, when it reacts with oxygen, it tends to form a peroxide—a compound known as lithium peroxide \( \mathrm{Li}_2\mathrm{O}_2 \). This particular behavior is characteristic of lithium due to its relatively small atomic size and high ionization energy.
However, as we delve into other group 1 metals like sodium and potassium, the mode of reaction changes. Sodium typically forms a different compound called sodium peroxide \( \mathrm{Na}_2\mathrm{O}_2 \), while potassium often forms a superoxide known as potassium superoxide \( \mathrm{KO}_2 \).
So, what's the difference? A superoxide features one oxygen atom as \( \mathrm{O}_2^- \), whereas a peroxide contains two oxygen atoms bonded together, as seen in \( \mathrm{O}_2^{2-} \). These differences influence the way these compounds react with water, ultimately affecting the products they form. This understanding is crucial for predicting outcomes in chemical reactions involving group 1 metals with oxygen.

Chemical Equations Balancing

Balancing chemical equations is essential in chemistry. It ensures that the same amount of each element is present on both sides of the equation.
Consider the lithium nitride reaction with water; writing it correctly requires knowing both reactants and products, then ensuring that atoms balance out:

• Start with \( \mathrm{Li}_3\mathrm{N} \), which means there are 3 lithium (Li) atoms and one nitrogen (N). Water \( (\mathrm{H}_2\mathrm{O}) \) introduces hydrogen and oxygen.
• Products \( \mathrm{LiOH} \) take up one lithium atom, one hydroxide (OH), and \( \mathrm{NH}_3 \), which balances the nitrogen and adds to the hydrogen count.
• Thus, 3 molecules of water balance 3 molecules of hydroxide and one ammonia.

Balancing brings a sense of satisfaction; it's like solving a puzzle that relies on the principle of conservation of mass. Once mastered, it becomes second nature in handling complex reactions and equations. It's not just about numbers; it's about understanding the underlying processes in chemical transformations.