Problem 130 - General Chemistry: Principles and Modern Applications

Question

If \(\mathrm{Br}^{-}\) and \(\mathrm{I}^{-}\) occur together in an aqueous solution, I can be oxidized to \(\mathrm{IO}_{3}^{-}\) with an excess of \(\mathrm{Cl}_{2}(\mathrm{aq})\) Simultaneously, \(\mathrm{Br}^{-}\) is oxidized to \(\mathrm{Br}_{2},\) which is extracted with \(\mathrm{CS}_{2}(1) .\) Write chemical equations for the reactions that occur.

Step-by-Step Solution

Answer

Equations for reactions: \(2 I^{-} (aq) + 2 Cl_{2} (aq) \rightarrow 2 IO_{3}^{-} + 4 Cl^{-}\) and \(2 Br^{-} (aq) + Cl_{2} (aq) \rightarrow 2 Br_{2} + 2 Cl^{-}\)

Step 1: Identify the initial state of substances

In this scenario, the initial state of the substances involved are \(Br^{-}\), \(I^{-}\) and \(Cl_2 (aq)\).

Step 2: Identify the final state of substances

The final state of the substances after oxidation are \(IO_3^{-}\) for \(I^{-}\) and \(Br_2\) for \(Br^{-}\).

Step 3: Write the balanced oxidation equations

For iodine - \(I^{-}\), we can write: \(2 I^{-} (aq) + 2 Cl_{2} (aq) \rightarrow 2 IO_{3}^{-} + 4 Cl^{-}\).For bromine - \(Br^{-}\), the equation will be: \(2 Br^{-} (aq) + Cl_{2} (aq) \rightarrow 2 Br_{2} + 2 Cl^{-}\). CS_2 is used to extract Br_2, but it does not participate in the actual reactions.

Key Concepts

Understanding Oxidation-Reduction Equations

When we speak about chemistry, one of the most significant reactions that occur is oxidation-reduction, commonly known as redox reactions. These are processes where electrons are transferred between substances, changing their oxidation states. In a redox reaction, one substance is oxidized by losing electrons, and another is reduced by gaining electrons.

In the provided exercise, we see iodide (\(I^{-}\)) and bromide (\(Br^{-}\)) ions being oxidized. Chlorine (\(Cl_2\text{(aq)}\)) acts as the oxidizing agent, causing iodide to become iodate (\(IO_3^{-}\)) and bromide to elemental bromine (\(Br_2\text{(l)}\)). When writing oxidation-reduction equations, it's crucial to ensure the transfer of electrons is equal and opposite for both the oxidizing and reducing agents. This ensures that the equation is balanced in terms of both mass and charge.

Aqueous Solution Reactions

Many chemical reactions occur in aqueous solutions, where water is the solvent. In an aqueous medium, the reactants, often in ionic form, interact and produce new products. Substances in aqueous solutions are dissociated into ions, which are free to move and react with other ions. This is why reactions in aqueous solutions can proceed rapidly.

For instance, in our exercise, when chlorine gas is dissolved in water, it reacts with the iodide and bromide ions. However, the product, bromine (\(Br_2\text{(l)}\)), is not soluble in water, thus it is extracted with carbon disulfide (\(CS_2\text{(l)}\)), highlighting the importance of solubility considerations in aqueous solution reactions.

Halogens Chemistry

The halogens include elements like fluorine, chlorine, bromine, and iodine, which are found in Group 17 of the periodic table. These elements are highly reactive, especially due to their seven valence electrons, wanting to gain one more to achieve a stable octet configuration. Halogens can undergo various chemical reactions, and they often act as oxidizing agents, as seen with chlorine in the textbook exercise.

Halogens can react with each other through interhalogen reactions. In our example, chlorine gas (\(Cl_2\text{(aq)}\)) oxidizes iodide to iodate and bromide to bromine. The reactivity of halogens decreases as you move down the group; therefore, chlorine can oxidize both iodide and bromide, which are below it in the periodic table.