Knowing what they know is half the battle: Investigating student conceptions of stoichiometry

Stoichiometry is a core topic in high school chemistry, yet it is often one of the most daunting for students as the extensive range of chemical and mathematical concepts required for understanding make this topic complex and challenging for student learning (Wink & Ryan, 2019; Ramful & Narod, 2014). The long-standing interest in research into student learning has afforded conceptions, misconceptions and alternative conceptions as vehicles through which researchers can investigate student understanding (Taber, 2015; Gilbert & Watts, 1983). Two-tier diagnostic instruments have been used extensively in previous research for this purpose where they have been useful in obtaining data regarding students’ conceptions of the relevant subject matter (Treagust, 1988; Soeharto et al., 2019). This study involved development of a two-tier diagnostic instrument to investigate the interplay between stoichiometry and mathematics. There were four steps to the development and refinement of the two-tier diagnostic instrument: defining the scope of the project, constructing the first tier, obtaining alternative conceptions, and developing the second tier. With multiple refinements during the design phase, the development of the instrument was informed by face validation from ten ‘critical friends’ alongside written responses from both undergraduate and graduate students (n = 24) and think-aloud interviews (n = 12). The final version of the two-tier diagnostic instrument contains 21 items comprising 14 chemistry items and 7 mathematics items. Development of a two-tier diagnostic instrument that addresses two interrelated subject matter areas is a novel application of the two-tier diagnostic approach and the implications of this will be presented.  REFERENCES Gilbert, J. K., & Watts, D. M. (1983). Concepts, Misconceptions and Alternative Conceptions: Changing Perspectives in Science Education. Studies in Science Education, 10(1), 61-98. Ramful, A., & Narod, F. B. (2014). Proportional reasoning in the learning of chemistry: levels of complexity, Mathematics Education Research Journal, 26(1), 25-46. Soeharto, S., Csapó, B., Sarimanah, E., Dewi, F., & Sabri, T. (2019). A Review of Students’ Common Misconceptions in Science and Their Diagnostic Assessment Tools. Jurnal Pendidikan IPA Indonesia. 8(2), 247-266. Taber, K. S. (2015). Alternative conceptions/frameworks/misconceptions. Encyclopedia of Science Education, pp 37-41. Treagust, D. F. (1988). Development and use of diagnostic tests to evaluate students’ misconceptions in science. International Journal of Science Education, 10(2), 159-169. Wink, D. J., & Ryan, S. A. C. (2019). The Logic of Proportional Reasoning and Its Transfer into Chemistry. It’s Just Math: Research on Students’ Understanding of Chemistry and Mathematics, pp 157-171

Assessment of total arsenic and arsenic species stability in alga samples and their aqueous extracts

In order to achieve reliable information on speciation analysis, it is necessary to assess previously the species stability in the sample to analyse. Furthermore, in those cases where the sample treatment for species extraction is time-consuming, an assessment of the species integrity in the extracts is of paramount importance. Thus, the present paper reports total arsenic and arsenic species stability in alga samples (Sargassum fulvellum and Hizikia fusiformis), as well as in their aqueous extracts, which were stored in amber glass and polystyrene containers at different temperatures. Total arsenic determination was carried out by inductively coupled plasma atomic emission spectroscopy (ICP-AES), after sample acid digestion in a microwave oven, while arsenic speciation was conducted by anion exchange high performance liquid chromatography on-line coupled to ICPAES, with and without sample introduction by hydride generation (HPLC-ICP-AES and HPLC-HG-ICP-AES), after aqueous microwave-assisted extraction. The results obtained for solid alga samples showed that total arsenic (for Hijiki alga) and arsenic species present (As(V) for Hijiki and NIES No. 9 Sargasso) are stable for at least 12 months when samples are stored in polystyrene containers at +20 ◦C. On the other hand, a different behaviour was observed in the stability of total arsenic and As(V) species in aqueous extracts for both samples, being the best storage conditions for Sargasso extracts a temperature of −18 ◦C and polystyrene containers, under which they are stable for at least 15 days, while Hijiki extracts must be stored in polystyrene containers at +4 ◦C in order to ensure the stability for 10 days

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic. An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed. Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min−1 flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g−1), Sargassum (38 ± 2 μg g−1) and Chlorella (9 ± 1 μg g−1) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g−1). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volum

Determination of toxic arsenic species and arsenosugars in edible seaweed by HPLC-(UV)-HG-AFS

Arsenic is a toxic element widely distributed in the environment, and the estimation of its toxicity requires knowledge of the individual arsenic species present in biological materials. Marine algae contribute substantial amounts of arsenic to the human diet in Asian countries, and nowadays their popularity in western countries is increasing due to their high mineral content and their recognized therapeutic properties1. It is known that marine organisms can accumulate considerable arsenic concentrations, up to ug g"1 level, which may be harmful to human beings. In seaweed, the main arsenic species are usually arsenoribosides (arsenosugars), which are considered to be non-toxic to living organisms and can be present at trace levéis, so analysis techniques of high sensitivity are needed to carry out their determination

Determination of soluble toxic arsenic species in alga samples by microwave-assisted extraction and high performance liquid chromatography-hydride generation-inductively coupled plasma-atomic emission spectroscopy

A microwave-based procedure for arsenic species extraction in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) is described. Extraction time and temperature were tested in order to evaluate the extraction efficiency of the process. Arsenic compounds were extracted in 8 ml of deionised water at 90 °C for 5 min. The process was repeated three times. Soluble arsenic compounds extracted accounted for about 78–98% of total arsenic. The results were compared with those obtained in a previous work, where the extraction process was carried out by ultrasonic focussed probe for 30 s. Speciation studies were carried out by high performance liquid chromatography–hydride generation–inductively coupled plasma-atomic emission spectrometry (HPLC-HG-ICP-AES). The chromatographic method allowed us to separate As(III), As(V), monomethylarsonic acid and dimethylarsinic acid in less than 13 min. The chromatographic analysis of the samples allowed us to identify and quantify As(V) in Hizikia sample and Sargasso material, while the four arsenic species studied were found in Chlorella sample. In the case of Laminaria sample, none of these species was identified by HPLC-HG-ICP-AES. However, in the chromatographic analysis of this alga by HPLC-ICP-AES, an unknown arsenic species was detected

Arsenic speciation in plants by HPLC-(UV)-HG-AFS: Optimisation of the extraction method and application to native plant species from soils polluted by mining activities

Se ha optimizado el método de extracción de especies de arsénico hidrosolubles en muestras de plantas terrestres procedentes de suelos contaminados por actividad minera. La especies extraídas se han determinado mediante HPLC-(UV)-HG-AFS

Application of ultrasound probe sonication for arsenic and heavy metal extraction in soils

Se ha optimizado un método de extracción de arsénico y metales pesados en suelos contaminados procedentes de actividad minera, mediante la aplicación de la sonda de ultrasonidos focalizada

Arsenic and heavy metal uptake and accumulation in native plant species from soils polluted by mining activities

Arsenic and heavy metal (specifically Cd, Cr, Cu, Ni, Pb, and Zn) uptake, translocation, and accumulation in ten native plant species spontaneously growing in soils polluted by mining activities were studied, with a focus on future phytoremediation work in polluted soils. Plant and soil samples were collected in the vicinity of the Mónica mine (NW Madrid, Spain). Soil analysis showed the ability of native plants for growing in soils with high concentration levels of Cd, Cu, Pb, Zn, and especially As. From these elements, the highest percentage of extractable elements was found for Cd and the lowest for Pb. A highly significant correlation was observed between total and extractable element concentrations in soils, except for Cu, indicating that total concentration is the most relevant factor for element mobility in these soils. Extractable elements in soils were better correlated with concentrations in plants than total elements in soils; thus, extraction methods applied are suitable to estimate the element phytoavailable fraction in soils, which depends on the plant species and not only on the element mobility in soils. High element concentrations were found in the aboveground parts of Corrigiola telephiifolia (As and Pb), Jasione montana (Cd and Zn), and Digitalis thapsi (As, Cd, Cu, Pb and Zn). However, considering the translocation and accumulation factors, together with the concentration levels found in roots and aboveground parts, only C. telephiifolia could be considered a Pb accumulator and an As hyperaccumulator plant, which could be used for future phytoremediation work in soils polluted with As

Light-cone distribution amplitudes of octet baryons from lattice QCD

We present lattice QCD results for the wave function normalization constants and the first moments of the distribution amplitudes for the lowest-lying baryon octet. The analysis is based on a large number of $N_f=2+1$ ensembles comprising multiple trajectories in the quark mass plane including physical pion (and kaon) masses, large volumes, and, most importantly, five different lattice spacings down to $a=0.039\,\mathrm{fm}$. This allows us to perform a controlled extrapolation to the continuum and infinite volume limits by a simultaneous fit to all available data. We demonstrate that the formerly observed violation of flavor symmetry breaking constraints can, indeed, be attributed to discretization effects that vanish in the continuum limit