Problem 104
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 the reaction of the white substance with water.
Step-by-Step Solution
Verified Answer
(a) The metal is potassium. (b) \( 2 \text{KO}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{KOH} + \text{H}_2\text{O}_2 + \text{O}_2 \).
1Step 1: Identifying Alkali Metal from Flame Test
The lilac-purple flame test suggests that the alkali metal is likely potassium (K), as potassium ions are known to produce a lilac or pink flame when burned.
2Step 2: Determine the Metal Oxide
Given that the alkali metal in question is potassium, the metal oxide formed by reacting potassium with oxygen should be potassium superoxide, which is denoted as \(\text{KO}_2\). This is consistent with the observation of a white solid that gives a positive test for \(\text{H}_2\text{O}_2\).
3Step 3: Write the Reaction for the Metal Oxide with Water
When potassium superoxide reacts with water, it forms potassium hydroxide (\(\text{KOH}\)), hydrogen peroxide (\(\text{H}_2\text{O}_2\)), and oxygen gas (\(\text{O}_2\)). The balanced chemical equation for this reaction is: \[ 2 \text{KO}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{KOH} + \text{H}_2\text{O}_2 + \text{O}_2 \]
Key Concepts
Flame TestAlkali MetalsPotassium Superoxide
Flame Test
The flame test is a simple yet effective method to identify certain metal ions based on the color they emit when heated. During this test, a sample of a compound is introduced into a flame, and the resulting color can be used to determine the presence of specific metals. This occurs because when the metal's electrons get excited by the heat, and then return to their original energy levels, they emit light of specific wavelengths, resulting in different colors. For instance, sodium shows a strong yellow flame, while lithium gives off a crimson red.
Potassium, the focus of our exercise, is unique for producing a lilac or pink flame. This distinct color is a key indicator of the presence of potassium ions in a compound. When analyzing unknown substances, scientists can rely on the flame test to quickly pinpoint the presence of alkali metals like potassium.
To perform the test, you generally need a clean wire loop, which you dip in hydrochloric acid and then into the substance being tested. You place the wire loop in the flame and look for the characteristic color. Though a simple procedure, the flame test is a powerful tool in the chemist’s toolkit for identifying metal ions within unknown compounds.
Potassium, the focus of our exercise, is unique for producing a lilac or pink flame. This distinct color is a key indicator of the presence of potassium ions in a compound. When analyzing unknown substances, scientists can rely on the flame test to quickly pinpoint the presence of alkali metals like potassium.
To perform the test, you generally need a clean wire loop, which you dip in hydrochloric acid and then into the substance being tested. You place the wire loop in the flame and look for the characteristic color. Though a simple procedure, the flame test is a powerful tool in the chemist’s toolkit for identifying metal ions within unknown compounds.
Alkali Metals
Alkali metals are a group of chemical elements found in Group 1 of the periodic table. This group includes lithium, sodium, potassium, rubidium, cesium, and francium. These metals are known for their high reactivity, especially with water and oxygen, making them fascinating yet challenging to use and store.
One striking characteristic of alkali metals is their soft texture and low densities, with some being light enough to float on water. They also have low melting points compared to most other metals, which is another reason for their vigorous reactions.
Because of their high reactivity, alkali metals are not found free in nature, but instead as salts or other compounds. Among them, potassium stands out due to its ability to form compounds like potassium superoxide, used in the absorption of carbon dioxide and generation of oxygen.
Despite their reactivity, alkali metals have essential roles in various chemical processes and daily applications. For example, sodium is crucial for biological functions, and lithium has applications in rechargeable batteries. Their unique properties make these metals a subject of continuous study and interest in the field of chemistry.
One striking characteristic of alkali metals is their soft texture and low densities, with some being light enough to float on water. They also have low melting points compared to most other metals, which is another reason for their vigorous reactions.
Because of their high reactivity, alkali metals are not found free in nature, but instead as salts or other compounds. Among them, potassium stands out due to its ability to form compounds like potassium superoxide, used in the absorption of carbon dioxide and generation of oxygen.
Despite their reactivity, alkali metals have essential roles in various chemical processes and daily applications. For example, sodium is crucial for biological functions, and lithium has applications in rechargeable batteries. Their unique properties make these metals a subject of continuous study and interest in the field of chemistry.
Potassium Superoxide
Potassium superoxide (\( ext{KO}_2\)) is an important compound formed when potassium reacts with oxygen. It belongs to a class of compounds known as superoxides, which contain an extra oxygen atom in comparison to ordinary oxides. This additional oxygen imparts unique characteristics to superoxides.
The chemical formula for potassium superoxide, \( ext{KO}_2\), can be broken down: it consists of potassium (\( ext{K}\)) and the superoxide ion (\( ext{O}_2^-\)). This compound forms a yellow or white solid and is particularly useful because of its ability to generate oxygen when reacted with water, a reaction that also produces potassium hydroxide and hydrogen peroxide.
As noted in the exercise, hydroxide and peroxide creation demonstrates its practical uses. Potassium superoxide provides life-supporting scenarios such as enclosed spaces or submersibles, where it can scrub carbon dioxide from the air and release oxygen, sustaining breathable environments.
The chemical formula for potassium superoxide, \( ext{KO}_2\), can be broken down: it consists of potassium (\( ext{K}\)) and the superoxide ion (\( ext{O}_2^-\)). This compound forms a yellow or white solid and is particularly useful because of its ability to generate oxygen when reacted with water, a reaction that also produces potassium hydroxide and hydrogen peroxide.
As noted in the exercise, hydroxide and peroxide creation demonstrates its practical uses. Potassium superoxide provides life-supporting scenarios such as enclosed spaces or submersibles, where it can scrub carbon dioxide from the air and release oxygen, sustaining breathable environments.
- Potassium superoxide's reaction with water is represented by the equation: \[2 ext{KO}_2 + 2 ext{H}_2 ext{O} \rightarrow 2 ext{KOH} + ext{H}_2 ext{O}_2 + ext{O}_2\]
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