Question

Make a general prediction about which of the halogen elements, \(\mathrm{F}_{2}, \mathrm{Cl}_{2}, \mathrm{Br}_{2},\) or \(\mathrm{I}_{2},\) displaces other halogens from a solution of halide ions. Which of the halogens is able to displace \(\mathrm{O}_{2}(\mathrm{g})\) from water? Which is able to displace \(\mathrm{H}_{2}(\mathrm{g})\) from water?

Short answer

Fluorine can displace all other halogens from their halide solutions. Chlorine, bromine, and iodine can displace the halogens below them in the Group 7. None of the halogens can displace oxygen from water. Only fluorine can displace hydrogen from water.

Step-by-step solution

Predicting the Halogen Displacement

Reactivity of halogens decreases down the group. This means, \( \mathrm{F}_{2} \) being at the top of the group is the most reactive and can displace all other halogens from their halide solution. Similarly, \( \mathrm{Cl}_{2} \) can displace \( \mathrm{Br}_{2} \) & \( \mathrm{I}_{2} \), \( \mathrm{Br}_{2} \) can only displace \( \mathrm{I}_{2} \), and \( \mathrm{I}_{2} \) being the least reactive, cannot displace any of the halogens.

Predicting the Displacement of \(\mathrm{O}_{2}(\mathrm{g})\) from Water

None of the halogens can displace oxygen from water. This is because oxygen is a strong oxidizing agent and less reactive than any halogen.

Predicting the Displacement of \(\mathrm{H}_{2}\)(g) from Water

Fluorine, being the strongest oxidising agent among the halogens, is the only one able to react with water to displace \( \mathrm{H}_{2}(\mathrm{g})\) . The reaction is: \(2 \mathrm{F}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 4 \mathrm{HF}(\mathrm{g})+ \mathrm{O}_{2}(\mathrm{g})\)

Key concepts

Displacement Reactions

Displacement reactions involve one element replacing another element in a compound. In the case of halogens, this means a more reactive halogen can displace a less reactive halide ion from a solution. The general rule to predict such reactions is that the higher up the halogen is in the periodic table, the more reactive it is.
This is why fluorine (\(\mathrm{F}_{2}\)) can displace any other halogens from their respective halide ions in solution, due to its high reactivity. Similarly, chlorine (\(\mathrm{Cl}_{2}\)) can displace bromine (\(\mathrm{Br}_{2}\)) and iodine (\(\mathrm{I}_{2}\)), while bromine can only displace iodine.

• Halogens that are more reactive can displace those that are less reactive from solutions.
• Check the position of the halogen in the periodic table to predict reactivity.

Halogen Series

The halogen series refers to Group 17 of the periodic table, which includes fluorine, chlorine, bromine, and iodine. These elements are known for their high reactivity, especially as they get higher in the group. This series shows a clear trend in chemical properties as you go down from fluorine to iodine. The elements become less reactive and have higher melting and boiling points.
Understanding this series is crucial to predict which elements will participate in displacement reactions. For example, fluorine is the most reactive halogen and is on top of the series, making it a strong candidate for displacing other halides.

• The halogen series shows a decrease in reactivity from top to bottom.
• Physical properties like melting and boiling points increase down the group.

Oxidizing Agents

An oxidizing agent is a substance that gains electrons in a chemical reaction, often causing another substance to be oxidized. Among halogens, fluorine stands as the strongest oxidizing agent. It means fluorine can easily accept electrons from other elements or compounds, making it highly reactive and capable of displacing less reactive halogens.
This characteristic allows fluorine to react with water to displace hydrogen gas, as it oxidizes water molecules. Meanwhile, oxygen, although a strong oxidizing agent itself, cannot be displaced from water by any halogens.

• Fluorine is the most potent oxidizing agent among the halogens.
• Oxidizing agents accept electrons during chemical reactions, causing oxidation.

Water Reactions

Water reactions involving halogens are interesting due to the role of the halogens as oxidizing agents. Fluorine is unique among halogens because it can react with water to form hydrofluoric acid (\(\mathrm{HF}\)) and oxygen gas (\(\mathrm{O}_{2}\)). This occurs because fluorine is a powerful oxidizer that can break water into its components and form new substances:
\[2 \mathrm{F}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 4 \mathrm{HF}(\mathrm{g})+ \mathrm{O}_{2}(\mathrm{g})\]No other halogen can undertake this drastic reaction with water due to their lesser reactivity. The ability of fluorine to displace hydrogen gas from water exemplifies its exceptional chemical activity.

• Fluorine can displace hydrogen from water, whereas other halogens cannot.
• Water reactions with halogens illustrate the concept of oxidizing potential.