The rapid development of information and communication technology provides an opportunity for scientists to develop a quantitative analytical method that is built on a mobile gadget as a detector. In this paper, we report a low-cost, simple and portable analytical method for mercury ion quantification based on digital image colorimetry coupled with a smartphone application. A small amount of silver nanoparticles (AgNPs) was used as a colorimetric agent that is selective only to mercury ions. The yellowish brown color of AgNPs instantly changed to colorless after the addition of mercury ions due to a redox reaction. To increase the portability, we attached the AgNPs onto a medium to create a paper-based analytical device. The final data processing of the colorimetric analysis was conducted using an android application available on the Google Play Store, called "Mercury Detector". The proposed method has good sensitivity, with a detection limit of 0.86 ppb, which is comparable to those of bulk and more expensive instruments. This allows for the detection of mercury ions as low as 2 ppb (10 nM), which is also the maximum contaminant level permitted in drinking water by the US Environmental Protection Agency. The proposed method was applied to real samples that provide satisfactory results on accuracy (2.4%) and precision (2.5%).

Beach sand is an abundant natural resource that contains silica minerals with many benefits. One of the uses of silica is to remove synthetic dyes that are toxic to biota in the environment. The goal of this research was to extract and characterize the silica from Bengkulu beach sand and to apply it as dyes adsorbent. The extraction of silica consisted of two steps that were potassium silicate formation and gel formation. The gel was formed by adding strong acid into a potassium silicate solution. Silica's particle size and crystallinity were characterized using PSA and XRD, respectively. SEM-EDS was used to characterize the morphology and chemical composition of extracted silica. The effect of the different experimental settings, like pH, temperature, contact time, the concentration of dyes and adsorbent weight, on adsorption of dyes were monitored as well as the study of adsorption isotherms, kinetics, and thermodynamics. At equilibrium, synthetic dyes adsorption to silica suited to the Freundlich model producing correlation coefficients (R 2 ) of 0.853 and 0.976 for remazol blue and congo red, respectively. At optimum conditions, maximum adsorption capacities for remazol blue and congo red were 133 and 131 mg/g, respectively. The research implied that adsorption of dyes to silica fitted the pseudo-second-order model with thermodynamic values of ∆G°, ∆H°, and ∆S° were -4.04 to 2.19 kJ/mol, -13.53 to -4.726 kJ/mol, and 0.019 to 0.021 J/mol.K, respectively. By using these results, we resolve that the adsorption of dyes trends was exothermic and spontaneous. In addition, the reaction increases the system's entropy. This study emphasizes the potential of silica from the sand beach as a substitute economical adsorbent for the toxic dyes removal.

Indonesia is one of the countries affected by the Covid-19 outbreak, where this situation greatly affects all aspects of life, including the field of education. The learning process is carried out online or in a network to minimize the spread of this virus, which makes learning effectiveness less than optimal, especially for material in the field of science. Selection of the right strategy and match the material is very necessary. The purpose of this study was to see the activities and learning outcomes of students using a blended learning-based discovery model on the subject of the Basic Laws of Chemistry. This research is a classroom action research conducted in two cycles. The research subjects were 26 students of the Biology Education Study Program in the first semester of the 2021/2022 class. The research data were obtained through observation sheets and cognitive tests using a test instrument in the form of a posttest. Based on the data analysis, it shows that the activities and student learning outcomes have increased from 54.62% and 66.25 in the first cycle to 87.69% and 80.48 in the second cycle. The students' understanding of the learning materials has included very good criteria.

The goal of this research was to make silver nanoparticles (NPP) with a cherry fruit extract bioreductor which was used for mercury metal analysis by using a digital image method. The process of making silver nanoparticles had done by a bottom up method involving a reduction reaction. The precursors used were 1 mM AgNO3 solution and as a bioreductor was an antioxidant compound which were in cherry fruit extract. Variation of the volume ratio between cherry fruit extract and 1 mM AgNO3 solution was 1: 3, 1: 4, 1: 5, 1: 6, and 1: 7 and the variation of contact time were 5, 15, 30, 45, 1, 2, 3 hours, and 1, 2, 7 days. The most optimum results of silver nanoparticles were synthesized with 1 : 4 volume ratio and 1 hour contact time. From the results of selectivity test, it was known that silver nanoparticles were made selective toward Hg and Fe metal. The sensitivity test toward Hg metal, it was known that NPP can detect mercury metal with the smallest concentration of 16,7  ppb.

ABSTRAKPenelitian ini bertujuan untuk mengembangkan media pembelajaran dalam bentuk video pembelajaran kimia dan digunakan untuk mengukur kemampuan berpikir kritis siswa. Metode yang digunakan adalah penelitian dan pengembangan (Research and Development) pembelajaran kimia pada bahan minyak bumi dengan model Dick dan Carey, melalui tahapan: desain, validasi, revisi dan tes formatif untuk siswa kelas XI di SMAN 1 Bengkulu Tengah. Kemampuan berpikir kognitif siswa dapat diukur dan dilihat dari hasil tes formatif, data yang diperoleh dalam bentuk data kuantitatif dan dilakukan analisis deskriptif untuk menilai kemampuan berpikir kritis siswa. Berdasarkan hasil tes formatif, 13,3% siswa kurang kritis, 60% siswa kritis, 20% siswa kritis dan 6,67% sangat penting. Kata kunci: Pengembangan; media; pembelajaran kimia; video; berfikir kritis. 0% 13,3 % 60% 20% 6,67%