A wash bottle water displacement scheme is used to determine the kinetics of the iodide-catalyzed H[subscript 2]O[subscript 2] decomposition reaction. The reagents (total volume 5.00 mL) are added to a test tube that is placed in a wash bottle containing water. The mass of the water displaced in [approximately]60 s is measured. The reaction is first order in H[subscript 2]O[subscript 2] and first order in I[superscript -]. The average rate constant reported by students is 0.0112 [plus or minus] 0.0002 M[superscript -1] s[superscript -1] (N = 17) at [approximately]20 [degree]C. (Contains 5 tables and 3 figures.)