Consider the following concentration–time data for the reaction of iodide ion and hypochlorite ion (OCl^-). The products are chloride ion and hypoiodite ion (OI^-).
(d) Propose a mechanism that is consistent with the rate law, and express the rate constant in terms of the rate constants for the elementary steps in your mechanism. (Hint: Transfer of an H⁺ ion between H₂O and OCl^- is a rapid reversible reaction.)

Verified step by step guidance

1. Identify the reactants and products in the given reaction. The reactants are iodide ion (I^-) and hypochlorite ion (OCl^-), and the products are chloride ion (Cl^-) and hypoiodite ion (OI^-).
2. Consider the hint provided about the rapid reversible reaction involving the transfer of an H⁺ ion between H₂O and OCl^-. Propose an initial fast equilibrium step where OCl^- reacts with H₂O to form HOCl and OH^-.
3. Propose a slow rate-determining step that involves the reaction of the intermediate HOCl with I^- to form hypoiodite ion (OI^-) and hydrogen ion (H⁺).
4. Write the overall reaction mechanism by combining the proposed steps and ensuring that the intermediates and any catalysts used appear on both sides of the equation and are canceled out.
5. Express the rate law based on the proposed mechanism. Use the steady-state approximation if necessary to relate the rate constants of the elementary steps to the observed rate constant of the overall reaction.

Key Concepts

Reaction Mechanism

A reaction mechanism is a step-by-step description of the pathway by which reactants are converted into products in a chemical reaction. It includes elementary steps, which are individual reactions that occur in sequence, and helps to explain the observed rate law. Understanding the mechanism allows chemists to predict how changes in conditions affect the reaction rate and product formation.

Rate Law

The rate law is an equation that relates the rate of a chemical reaction to the concentration of its reactants. It is typically expressed in the form rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B. The rate law provides insight into the relationship between concentration and reaction speed, and it can be derived from experimental data.

Elementary Steps and Rate Constants

Elementary steps are the individual reactions that make up a reaction mechanism, each with its own rate constant. The overall rate constant for a complex reaction can be expressed in terms of the rate constants of these elementary steps, often involving the slowest step, which determines the overall reaction rate. Understanding how to relate these constants is crucial for proposing a valid mechanism consistent with the observed rate law.