Problem 58 - Chemistry The Central Science In Si Units

Question

The following reactions (note that the arrows are pointing only one direction) can be used to prepare an activity series for the halogens: $$ \begin{aligned} \mathrm{Br}_{2}(a q)+2 \operatorname{Nal}(a q) & \longrightarrow 2 \mathrm{NaBr}(a q)+\mathrm{I}_{2}(a q) \\ \mathrm{Cl}_{2}(a q)+2 \mathrm{NaBr}(a q) & \longrightarrow 2 \mathrm{NaCl}(a q)+\mathrm{Br}_{2}(a q) \end{aligned} $$ (a) Which elemental halogen would you predict is the most stable, upon mixing with other halides? (b) Predict whether a reaction will occur when elemental chlorine and potassium iodide are mixed. (c) Predict whether a reaction will occur when elemental bromine and lithium chloride are mixed.

Step-by-Step Solution

Answer

Iodine is the most stable halogen. A reaction will occur with chlorine and potassium iodide, but no reaction with bromine and lithium chloride.

Step 1: Analyze Reaction 1

The reaction \( \mathrm{Br}_{2}(aq) + 2 \mathrm{NaI}(aq) \rightarrow 2 \mathrm{NaBr}(aq) + \mathrm{I}_{2}(aq) \) shows bromine displacing iodine from sodium iodide, resulting in the formation of sodium bromide and iodine. This indicates that bromine is a stronger oxidizing agent than iodine.

Step 2: Analyze Reaction 2

The reaction \( \mathrm{Cl}_{2}(aq) + 2 \mathrm{NaBr}(aq) \rightarrow 2 \mathrm{NaCl}(aq) + \mathrm{Br}_{2}(aq) \) shows chlorine displacing bromine from sodium bromide, producing sodium chloride and bromine. This indicates that chlorine is a stronger oxidizing agent than bromine.

Step 3: Determine the Most Stable Halogen

Based on Reactions 1 and 2, since chlorine can displace bromine, and bromine can displace iodine, it suggests that iodine is the least active among these halogens. Thus, iodine is predicted to be the most stable halogen upon mixing with other halides.

Step 4: Predict Reaction with Chlorine and Potassium Iodide

Chlorine is a stronger oxidizing agent than iodine, as seen from the earlier reactions. Thus, when chlorine is mixed with potassium iodide (\( \mathrm{KI} \)), chlorine will displace iodine, leading to a reaction that forms potassium chloride (\( \mathrm{KCl} \)) and iodine (\( \mathrm{I}_2 \)).

Step 5: Predict Reaction with Bromine and Lithium Chloride

Bromine is not strong enough to displace chlorine, which is more active, from lithium chloride (\( \mathrm{LiCl} \)). Therefore, no reaction will occur when bromine is mixed with lithium chloride.

Key Concepts

Halogens

Halogens are a unique group of elements found in Group 17 of the periodic table. This family of elements includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements share some common properties that make them fascinating and important in chemical reactions.

Some key characteristics of halogens include:

• They are highly reactive non-metals. Their reactivity is due to their seven valence electrons, which makes them eager to gain one more electron to achieve a stable octet electron configuration.
• Their reactivity decreases down the group. This means that fluorine is the most reactive, while astatine is the least reactive among the halogens.
• They can exist in different states of matter at room temperature: fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids.

The vivid colors they exhibit, such as the green of chlorine gas and the reddish-brown of bromine liquid, make them quite visible and useful in many visual demonstrations of chemical reactions.

Oxidizing Agents

An oxidizing agent is a substance that gains electrons in a chemical reaction and, in the process, oxidizes another substance. In simpler terms, it is a chemical that helps another chemical lose electrons.

Here are some important points about oxidizing agents:

• They help drive chemical reactions, specifically oxidation-reduction (redox) reactions, by accepting electrons from other elements or compounds.
• Within the halogens, the strength of oxidizing agents varies. Chlorine is known to be a stronger oxidizing agent than bromine, as it can displace bromine from compounds due to its higher affinity for electrons.
• Oxidizing agents are crucial in many processes, ranging from industrial applications to biological systems, where they help in the degradation of organic substances.

In chemical equations, a powerful oxidizing agent will often appear on the reactant side and be reduced to a lower oxidation state during the reaction.

Displacement Reactions

Displacement reactions, specifically single displacement reactions, are a type of chemical reaction where an element reacts with a compound and takes the place of another element in that compound. This is a classic example of how reactive elements interact with less reactive elements.

In the context of halogens, a more reactive halogen can displace a less reactive halogen from a halide compound:

• Displacement reactions provide valuable insight into the reactivity series of elements. By observing which halogen displaces another from its compounds, we can deduce the order of reactivity among the halogens.
• The general reaction format: \[ ext{A} + ext{BC} ightarrow ext{AC} + ext{B} \]where element A is more reactive than B.
• In the activity series of halogens, chlorine can displace bromine and iodine from their halide compounds. This confirms that chlorine is more reactive than both bromine and iodine.

Understanding displacement reactions helps in predicting how elements will behave in mixtures, which is useful in laboratory and industrial settings.