Clock Reaction Revisited: Catalyzed Redox Substrate-Depletive Reactions

Abstract

Quantitative demonstration of chemical kinetics often requires sophisticated equipment and materials. By using inexpensive and commonly available chemicals, we propose here two clock reactions, oxygen–safranin–benzoin clock and cysteine–iodine–hydrogen peroxide clock. Students simply measure and add stock solutions to start clock reactions. Sudden discoloration or coloration of the reaction mixture marks the end of the reaction, and this can be conveniently timed. Students then complete calculations and graphing in a spreadsheet file by following common protocols. Rates of reaction are calculated from the ratio of [limiting reactant]0 and clock time. Orders of reactions and rate constants are determined by the method of initial rate. Additional discussions on topics such as catalysis, reaction mechanism, redox reaction, and pseudo-zeroth-order reaction are also possible.

Continuous Addition Kinetic Elucidation: Catalyst and Reactant Order, Rate Constant, and Poisoning from a Single Experiment

“…23 Following the successful fitting of a reaction which was first order in both reactant and catalyst it was decided that reactions with different orders should be examined. Therefore, we next tested a reaction that was zero order in the reactant under study, namely the famous iodine clock reaction, 24 in this case, with Icatalyzing the oxidation of ascorbic acid. The first step of the reaction is the rate-limiting combination of excess H 2 O 2 + Ito make I 2 .…”

Enhancing Student Engagement with a Small-Scale Car That Is Motion-Controlled through Chemical Kinetics and Basic Electronics

“…By substituting eq in eq , the switchover time can be rewritten as Equation can also be obtained through the pseudo-zeroth-order clock reaction model applied for a vitamin C–iodine–H 2 O 2 system under the catalyzed redox substrate–depletive reactions approach. In this approach, vitamin C is the limiting reagent, iodine is not viewed as a product but as a catalyst in the clock, and the only reagents consumed in the total reactive system are vitamin C (the reducing agent) and H 2 O 2 (the oxidizing agent).…”

Inhibition of the urea-urease reaction by the components of the zeolite imidazole frameworks-8 and the formation of urease-zinc-imidazole hybrid compound

“…A clock reaction (or chemical clock) is a type of chemical reaction in which the product appears suddenly with a well-defined time lag after starting the reaction [1][2][3]. The lag time is also defined as Landolt time after the iodine clock reaction discovered by Heinrich Landolt [4].…”