A student investigates the reaction between bromate ion and iodide ion in acidic solution
CHEMISTRY · Multi-part · A Level · Chemistry · Introduction to organic chemistry · Introduction to organic chemistry
Problem
A student investigates the reaction between bromate ion and iodide ion in acidic solution, which is known to produce iodine. The student proposes the following multistep mechanism. Sodium ions (Na+) are present in the reaction mixture as part of the buffer.
Elementary steps:
1. BrO3−+I−+2H+→HBrO2+HOI
2. HBrO2+I−+H+→HOI+HOBr
3. HOBr+I−+H+→HOI+Br−+H2O
Sodium ions are spectator ions that do not participate in any elementary step.
Answer the following questions about the mechanism and the role of various species.
(a) Write the overall balanced equation for the reaction after canceling any species that appear on both sides of the summed elementary steps.
(b) List each species that is produced in an early step and consumed in a later step. For each such species, state whether it is an intermediate or a catalyst, and justify your answer with evidence from the mechanism and the overall equation.
(c) Explain why Na+ is classified as a spectator ion rather than as a catalyst, even though it is present before and after the reaction.
(d) The student observes that increasing the concentration of Na+ has no measurable effect on the reaction rate. Explain how this observation supports your classification of Na+ in part (c).