Problem 72 - Chemistry The Central Science

Question

(a) One of the alkali metals reacts with oxygen to form a solid white substance. When this substance is dissolved in water, the solution gives a positive test for hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). When the solution is tested in a burner flame, a lilac-purple flame is produced. What is the likely identity of the metal? (b) Write a balanced chemical equation for reaction of the white substance with water.

Step-by-Step Solution

Answer

The alkali metal is potassium (K), and the white substance is potassium superoxide (KO2). The balanced chemical equation for the reaction of KO2 with water is: \(2\, KO_{2} (s) + 2\, H_{2}O (l)\rightarrow 2\, KOH (aq) + H_{2}O_{2} (aq) + O_{2} (g)\).

Step 1: Identify the alkali metal based on given properties

Based on the given information, we know that: 1. The metal reacts with oxygen to form a solid white substance. 2. The resulting substance produces hydrogen peroxide when dissolved in water. 3. The metal produces a lilac-purple flame color when tested in a burner flame. The flame color is a strong indication of the metal's identity. The alkali metal that produces a lilac-purple flame is potassium (K).

Step 2: Determine the white substance formed by the reaction

We know that the reaction involves potassium (K) and oxygen (O), and the resulting white substance is likely a potassium oxide. The most common potassium oxide is potassium superoxide (KO2).

Step 3: Write the balanced chemical equation

We are asked to write the balanced chemical equation for the reaction of potassium superoxide (KO2) with water (H2O). The reaction is as follows: \(2\, KO_{2} (s) + 2\, H_{2}O (l)\rightarrow\) 2 KOH (aq) + H2O2(aq) + O2(g) The chemical equation is now balanced.

Key Concepts

Potassium Reaction

Potassium is a part of the alkali metals group on the periodic table. These metals are well-known for their vigorous reactions with other elements, especially with oxygen. When potassium interacts with oxygen, it forms potassium oxides. Unlike simple oxides, potassium forms a unique compound known as potassium superoxide when it reacts with oxygen. The chemical formula for this compound is KO2. This compound appears as a solid white substance, making it easy to identify in laboratory conditions.

The reason potassium and other alkali metals are so reactive is due to their single valence electron which they are eager to lose to achieve a stable electron arrangement. When potassium loses this electron to oxygen, a highly reactive reaction occurs, producing both heat and light.

• Reacts readily with oxygen
• Forms white potassium superoxide (KO2)
• Highly reactive due to single valence electron loss

Potassium superoxide plays a significant role in chemical reactions. When dissolved in water, it produces hydrogen peroxide, a fact that hints at its oxygen-rich nature. This aspect of its reactivity is crucial for understanding both earth-based and even space-based applications, especially in generating oxygen for enclosed environments.

Flame Test

The flame test is a fascinating method in chemistry used to help identify the presence of certain metal ions based on the color of the flame they produce when heated. Specific colors are produced because of the distinct energy transitions the electrons undergo within the metal ions. When it comes to potassium, it emits a remarkable lilac or purple flame. This signature color is a direct result of electronic transitions within potassium atoms.

As potassium atoms are heated, their electrons are excited to higher energy levels. When these electrons return to their ground state, they release energy in the form of visible light. The wavelength of this light corresponds to the lilac color observed in the flame test. It's important to note that although potassium's flame color may appear faint, it's still quite definitive in the laboratory setting. This fascinating method provides an immediate, visual way to identify potassium among the other alkali metals.

• Lilac-purple flame is distinctive for potassium
• Color results from electronic energy transitions
• Used to identify metal ions quickly and visually

A flame test is not just fascinating but also an invaluable tool in educational settings, demonstrating the varied behavior of elements.

Potassium Superoxide

Potassium superoxide (KO2) is a noteworthy compound due to its formation and functionality. It is produced through the reaction of potassium metal with oxygen, making it an oxide rich in oxygen. The formation of potassium superoxide is quite distinctive because, unlike simpler metal oxides, it incorporates additional oxygen molecules, resulting in a superoxide rather than just a regular oxide. This substantial oxygen presence is a key reason why it can yield hydrogen peroxide when interacting with water.

The balanced chemical equation that represents the reaction of potassium superoxide with water is:\[2\, KO_{2} (s) + 2\, H_{2}O (l)\rightarrow 2\, KOH (aq) + H2O2(aq) + O2(g)\]In this reaction:

• Potassium superoxide (KO2) reacts with water
• Produces potassium hydroxide (KOH)
• Releases hydrogen peroxide (H2O2) and oxygen gas (O2)

This transformation plays a crucial role in chemical and industrial applications, particularly in settings where emergency oxygen supply is vital, such as in submarines or space missions. Understanding this compound's properties has broad implications for both scientific research and practical uses.