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This article describes the development and application of a two-tier multiple choice diagnostic instrument to assess high school students' understanding of inorganic chemistry qualitative analysis. The development of the diagnostic instrument was guided by the framework outlined by Treagust. The instrument was administered to 915 Grade 10 students (15 to 17 years old) from 11 schools after they had learned the theory involved in qualitative analysis and after a series of qualitative analysis practical sessions. The Cronbach alpha reliability of the instrument was .68, the facility indices ranged from .17 to .48, and the discrimination indices ranged from .20 to .53. The study showed that the Grade 10 students had dif®culty understanding the reactions involved in the identi®cation of cations and anions, for example, double decomposition reactions, the formation and reaction of complex salts, and thermal decomposition. The ®ndings of the study and literature on practical work were used to develop a qualitative analysis teaching package. ß

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The topic of ionisation energy is important as the concepts involved provide the foundation for the understanding of atomic structure, periodic trends and energetics of reactions. Previous research has shown that A-level (high school) students in the United Kingdom had difficulty understanding the concepts involved in ionisation energy. This paper describes the development and administration of a two-tier, multiple-choice instrument on ionisation energy, the Ionisation Energy Diagnostic Instrument, to determine if A-level students (Grade 11 and 12, 17 to 18 years old) in Singapore have similar alternative conceptions to those of their counterparts in the United Kingdom, as well as explore their understanding of the trend of ionisation energies across Period 3. The items in such instruments are specifically designed to identify alternative conceptions and misunderstandings in a limited and clearly defined content area. The results showed that students in Singapore applied the same octet rule framework and conservation of force thinking to explain the factors influencing ionisation energy as the students in the United Kingdom. In addition to the above alternative frameworks, many students in Singapore also resorted to relation-based reasoning to explain the trend of ionisation energies across Period 3 elements. [Chem.

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A study of the involvement of free oxygen radicals in trapping and digestion of insects by carnivorous plants was the main goal of the present investigation. We showed that the generation of oxygen free radicals by pitcher fluid of Nepenthes is the first step of the digestion process, as seen by EPR spin trapping assay and gel-electrophoresis. The EPR spectrum of N. gracilis fluid in the presence of DMPO spin trap showed the superposition of the hydroxyl radical spin adduct signal and of the ascorbyl radical signal. Catalase addition decreased the generation of hydroxyl radicals showing that hydroxyl radicals are generated from hydrogen peroxide, which can be derived from superoxide radicals. Gel-electrophoresis data showed that myosin, an abundant protein component of insects, can be rapidly broken down by free radicals and protease inhibitors do not inhibit this process. Addition of myoglobin to the pitcher plant fluid decreased the concentration of detectable radicals. Based on these observations, we conclude that oxygen free radicals produced by the pitcher plant aid in the digestion of the insect prey.