International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What effect does chlorine have on potassium iodide in an aqueous solution?

1. It forms a colorless solution

2. It reduces it to potassium chloride

3. It oxidizes it to iodine

4. It maintains its color

The correct answer is: It oxidizes it to iodine

When chlorine is added to potassium iodide in an aqueous solution, it acts as an oxidizing agent. Chlorine has a higher oxidation potential than iodide ions, allowing it to oxidize the iodide ions (I⁻) to iodine (I₂). This reaction leads to the formation of molecular iodine, which typically appears as a brown solution due to the color of iodine. The oxidation of iodide to iodine can be represented by the following half-reaction: \[ 2 \text{I}^- \rightarrow \text{I}_2 + 2 \text{e}^- \] In this process, the chlorine is simultaneously reduced, which can be depicted in a balanced chemical equation involving the conversion of Cl₂ to Cl⁻. Hence, this interaction results in the emergence of a visible color change in the solution, confirming the formation of iodine. The other options do not accurately capture the chemical behavior taking place in this scenario. A colorless solution does not result from this reaction because iodine imparting a brown color is a characteristic feature. While the term potassium chloride refers to the potential products of the reaction, chlorine does not reduce potassium iodide to this compound in this context. Finally, maintaining its color contradicts the