Question

If \(\mathrm{I}_{2}\) and \(\mathrm{Br}_{2}\) are added to a solution containing \(\mathrm{I}^{-}\) and \(\mathrm{Br}^{-}\), what reaction will occur if the concentration of each species is \(1 \mathrm{~m}\) ?

Short answer

In the given scenario with equal concentrations (1 M) of I2, Br2, I-, and Br-, the reaction that will occur is the oxidation of iodide ion (I-) to iodine (I2) and the reduction of bromine molecule (Br2) to bromide ion (Br-). The overall balanced equation for this reaction is: \( 2\text{I}^- + \text{Br}_2 \rightarrow \text{I}_2 + 2\text{Br}^- \).

Step-by-step solution

1. Identify the Standard Reduction Potentials

Lookup the standard reduction potentials for I2/I- and Br2/Br- in the Table of Standard Reduction Potentials. The standard reduction potentials are as follows: \[ \text{I}_2 + 2e^- \rightarrow 2\text{I}^-, E^\circ = +0.54 \text{V} \quad \text{(1)} \] \[ \text{Br}_2 + 2e^- \rightarrow 2\text{Br}^-, E^\circ = +1.09 \text{V} \quad \text{(2)} \]

2. Determine the Strongest Reducing and Oxidizing Agents

The species that gets reduced has the highest standard reduction potential. From equations (1) and (2), Br2 has a higher reduction potential (+1.09V) than I2 (+0.54V). Hence, Br2 will be reduced. The species that gets oxidized is the one with the lower standard reduction potential in its reverse form (since oxidation is the reverse of reduction). I- will be oxidized because its equation reversed from (1) has a lower reduction potential.

3. Write Down the Oxidation and Reduction Half-Reactions

The reduction half-reaction involves Br2: \[ \text{Br}_2 + 2e^- \rightarrow 2\text{Br}^- \quad \text{(reduction)} \] The oxidation half-reaction involves I-: \[ 2\text{I}^- \rightarrow \text{I}_2 + 2e^- \quad \text{(oxidation)} \]

4. Combine the Half-Reactions to Obtain the Full Reaction

Combine these two half-reactions to obtain the full balanced equation. The final reaction is: \[ 2\text{I}^- + \text{Br}_2 \rightarrow \text{I}_2 + 2\text{Br}^- \quad \text{(overall reaction)} \] This is the reaction that will occur when I2, Br2, I- and Br- (all of concentration 1 M) are mixed.

5. Summarize the Findings

In conclusion, the reaction that will occur involves the oxidation of I- to I2 and the reduction of Br2 to Br-. The iodide ion (I-) will lose electrons and the bromine molecule (Br2) will gain them.

Key concepts

Redox Reactions

Redox reactions stand for reduction-oxidation reactions. They are chemical processes in which the state of oxidation of atoms is changed. Redox reactions play a crucial role in various scientific fields like chemistry and biology. In any redox reaction, there is always one substance that gets oxidized and another that gets reduced.
- **Reduction** refers to the gain of electrons or decrease in oxidation state by a molecule, atom, or ion. - **Oxidation** means the loss of electrons or an increase in oxidation state. A helpful way to remember this is by using the mnemonic "LEO the lion says GER" where LEO stands for "Losing Electrons is Oxidation" and GER stands for "Gaining Electrons is Reduction." In a redox reaction, electrons are transferred from one reactant to another, leading to changes in oxidation states.

Oxidation and Reduction

Understanding oxidation and reduction involves recognizing how electrons are transferred between species in a chemical reaction. In the exercise, we can identify which species are oxidized or reduced by looking at their standard reduction potential.
Oxidation occurs when an atom or ion loses electrons. In our case, the iodide ion ( I^- ) loses electrons to form iodine ( I_2 ). Reduction happens when an atom or ion gains electrons. For this exercise, bromine ( Br_2 ) gains electrons to form bromide ions ( Br^- ).
These processes happen simultaneously: while one species loses electrons (oxidized), the other gains the electrons (reduced). Recognizing the species that lose or gain electrons will help you understand their roles in the chemical processes.

Half-Reaction Method

The half-reaction method is a step-by-step way to balance redox reactions. It separately considers the oxidation and reduction processes before combining them to give the overall reaction.
1. **Identify Half-Reactions**: Break down the full reaction into two halves: oxidation and reduction. - In our scenario, identify I^- oxidizing to I2 and Br2 reducing to Br-. 2. **Balance Electrons**: Ensure that the number of electrons lost in the oxidation half matches those gained in the reduction half. Electrons must be balanced for the overall reaction to conserve charge. 3. **Combine Balanced Half-Reactions**: After balancing electrons, add the two half-reactions together to get the complete balanced redox equation.
This method emphasizes charge and mass conservation in chemical equations.

Electrochemistry

Electrochemistry focuses on the interplay between chemical reactions and electricity. It’s the study of how chemical reactions can produce electric currents, and vice versa.
In electrochemical cells, redox reactions occur allowing us to harness electrical energy. These cells are composed of electrodes known as anodes and cathodes, immersed in electrolytic solutions. - **Anode**: Site of oxidation - **Cathode**: Site of reduction
Electrochemical processes have practical applications in batteries, electrolysis, and corrosion prevention. In the exercise problem, we see a redox reaction that could theoretically be harnessed for electricity in an electrochemical cell. Understanding the basics of electrochemistry allows us to better comprehend how redox reactions influence the flow of electrons and energy conversion.