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Teaching complex chemistry concepts such as kinetics using inquiry-based learning techniques can be challenging in a high school classroom setting. Access to expensive laboratory equipment such as spectrometers is typically limited and most reaction kinetics experiments have been designed for advanced placement (AP) or first-year undergraduate courses. Therefore, we developed a new and inexpensive laboratory experiment specially tailored for high school students. The activities include in situ monitoring of iodide oxidation using individual UV-visible spectrophotometers, data analysis with a spreadsheet, and interpretation. The experiment introduces chemical kinetics, offers practice problems, and teaches students the technique of flooding to acquire data and make connections with reaction mechanisms based on trends observed in the rate constants. The exercise was successful in solidifying the concepts of rates, rate laws, reaction order, and their relation to mechanistic studies. The provided handout and notes are tailored to help high school science teachers implement the Next Generation Science Standards in their classrooms. [ABSTRACT FROM AUTHOR]

The decomposition of the title compound (H(2)O)(5)CrOOH(2+) (hereafter Cr(aq)OOH(2+)) in acidic aqueous solutions is kinetically complex and generates mixtures of products (Cr(aq)(3+), HCrO(4)(-), H(2)O(2), and O(2)). Relative yields of individual products vary greatly with reaction conditions and initial concentrations of Cr(aq)OOH(2+). At pH 5.5 in the presence of O(2), the reaction was complete in less than a minute and generated chromate in about 70% yield. These findings, in addition to poor reproducibility of kinetic data, are indicative of the involvement of one or more reactive intermediates that consume additional amounts of Cr(aq)OOH(2+) in post-rate-determining steps. The kinetics were simplified in the presence of H(2)O(2) or ABTS(2-), both of which are capable of scavenging strongly oxidizing intermediates. The measured rate constant in 0.10 M HClO(4) at low O(2) concentrations (≤0.03 mM) was independent of the concentration of the scavengers and was, within error, the same for ABTS(2-), k = 4.9 (±0.2) × 10(-4) s(-1), and H(2)O(2), k = 5.3 (±0.7) × 10(-4) s(-1). At a constant ionic strength of 1.0 M, the reaction in the presence of either H(2)O(2) or ABTS(2-) obeyed a two-term rate law, k(obs)/s(-1) = 6.7 (±0.7) × 10(-4) + 7.6 (±1.1) × 10(-4) [H(+)]. Both in the presence and absence of ABTS(2-) as the scavenger, the yields of H(2)O(2) increased with increasing [H(+)]. These results are discussed in terms of a dual-pathway mechanism for the decay of Cr(aq)OOH(2+). The H(+)-catalyzed path leads to the dissociation of H(2)O(2) from Cr(III), while in the H(+)-independent reaction, Cr(aq)OOH(2+) is transformed to Cr(V). Both scavengers rapidly remove Cr(V) and simplify both the kinetics and products.