Information about score obtained from a test is often interpreted as an indicator of the student's ability level. This is one of the weaknesses of classical analysis that are unable to provide meaningful and fair information. The acquisition of the same score if it comes from a test item with a different level of difficulty, must show different abilities. Analysis of the Rasch model will overcome this weakness. The purpose of this study was to analyze the quality of the items by validating the national chemistry exam instrument using the Rasch model. The research sample was 212 new students of the Department of Chemistry at the State University of Medan. The data collected was in the form of respondent's answer data to the 2013 chemistry UN questions, which amounted to 40 items multiple choice and uses the documentation method. Data analysis technique used the Rasch Model with Ministep software. The results of the analysis show the quality of the Chemistry National Exam (UN) questions is categorized as very good based on the following aspects: unidimension, item fit test, person map item, difficulty test level, person and item reliability. There is one item found to be gender bias, in which men benefit more than women. The average chemistry ability of respondents is above the average level of difficulty of the test items
This research is part of the development research in solution chemistry-HOTS-Tawheed. The purpose of this research is to develop of instrument test Higher Order Thinking Skills (HOTS) based on Tawheed on solution chemistry. The stages of the research began by designing 40 multiple choice item with five options. The instrument assessed by five science education experts. Expert judgement analysis of the test item was carried out using the Rasch measurement model approach, facets software. The Multi-rater validation test results showed: (1) The five expert panels considered quality items 23 out of 40 (57.5%); (2) according to the five validators, the instrument items that are most difficult to fulfill from the questions are statements B4, K4, and K8 (logit>+1), while K10 (logit<-4) is the statement item that is easiest to fulfill from the questions; (3) aspect of statistical fit criteria, it can be seen that Val.A and Val.F experts are the most consistent (based on MNSQ and ZSTD); (4) the reliability of the items showed a good level (0.97); and (5) the similarity of assessment by the five experts (exact agreement) which reached 93.0% which shows that there was not much difference between the five experts in assessing all the items.
This research is motivated by the low ability of students in developing critical thinking skills and problem solving and the lack of student motivation to develop science and link chemistry with other science. This research is a quantitative research. This study aims to determine the effectiveness of STEM-based modules on learning outcomes and student motivation. The type of research used is a quasi-experimental design using a non-equivalent control group pretest-posttest design. The data collection method used was a multiple choice test to measure learning outcomes and a questionnaire to analyze learning motivation. The results showed that the use of STEM-based modules had an effect on student learning outcomes and learning motivation in selected subjects.
The purpose of this study was to determine the stability and structure on the interaction between β-carotene compounds with methanol, ethanol, acetone, chloroform, carbon tetrachloride, cyclohexane, and n-hexane compounds. This research is a molecular modeling using computational chemistry calculations with the function/basis set RHF/3-21G and B3LYP/3-21G. The computational chemistry calculations used Gaussian 09 Revision D 01 and visualization used the Jmol and Avogadro software. The data obtained from computational chemistry calculations with the function/basis set RHF/3-21G on the interaction between β-carotene -methanol compounds are ΔE = -11.899 kJ / mol, β-carotene -ethanol ΔE = -12.256 kJ/mol, β-carotene -acetone ΔE = -9.276 kJ/mol, β-carotene -chloroform ΔE = 5.262 kJ/mol, β-carotene -carbon tetrachloride ΔE = 3.747 kJ/mol, β-carotene-cyclohexane ΔE = 2.691 kJ/mol, β-carotene-n-hexane ΔE = 6.453 kJ/mol. The data obtained with the function/basis set B3LYP/3-21G on the interaction between β-carotene-methanol compounds are ΔE = -24.588 kJ/mol, β-carotene -ethanol ΔE = -25.123 kJ/mol, β-carotene -acetone ΔE = -18.140 kJ/mol, β-carotene -chloroform ΔE = 2.255kJ/mol, β-carotene -carbon tetrachloride ΔE = -1.187 kJ/mol, β-carotene-cyclohexane ΔE = -0.801 kJ/mol, β-carotene -hexane ΔE = -0.412 kJ/mol. Based on the analysis of thermodynamic data from computational chemistry calculations with the function / basis set UHF/3-21G and B3LYP/3-21G, it was found that β-carotene-ethanol and β-carotene-methanol mixtures had very stable mixtures.
Sungai adalah salah satu sumber air yang digunakan oleh manusia untuk berbagai aktivitas dalam kehidupan dan memiliki peranan penting dalam kehidupan setiap makhluk hidup sehingga air akan mempengaruhi dan dipengaruhi oleh kondisi/ komponen lainnya. Penelitian ini bertujuan untuk menganalisis kandungan logam berat Timbal (Pb) dalam air sungai silau di kota kisaran dan tingkat pencemarannya yang dibandingkan dengan standar baku air dalam PP No 82 tahun 2001. Penelitian dilakukan pada bulan Juni - September 2017. Pengambilan sampel air sungai menggunakan metode purposive sampling yang diambil dari tiga stasiun sungai silau di kota kisaran. Parameter yang dianalisis adalah tingkat pencemaran logam berat Timbal (Pb) dalam air sungai silau menggunakan alat Atomic Absorption Spectrophotometry (AAS) melalui uji-t satu pihak dan data kuesioner yang diperoleh dari masyarakat yang bertempat tinggal di sekitar pinggir sungai Silau yang diolah menggunakan aplikasi SPSS 16.0. Hasil analisis data menyatakan bahwa air sungai silau telah teridentifikasi mengandung logam berat Timbal (Pb) sehingga perlu pengawasan yang rutin untuk mengantisipasi agar tidak terjadinya pencemaran logam berat Timbal (Pb). Hasil uji hipotesis menyatakan bahwa konsentrasi logam berat timbal (Pb) tidak berbeda signifikan dengan standar baku air dalam Peraturan Pemerintah No. 82 tahun 2001 sehingga diperoleh kesimpulan bahwa air sungai silau tidak tercemar logam berat Timbal (Pb) dan tidak terdapat dampak negatif secara langsung bagi kesehatan masyarakat sekitar. Hal ini didukung oleh data kuesioner yang menyimpulkan bahwa tidak ada masyarakat yang mengalami keluhan kesehatan yang dipengaruhi oleh keberadaan logam berat Timbal (Pb).
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