Chemical (Silicate) Garden, One Experiment for Education in STEM Field

Vizualizacija kemijskih procesa iznimno je važna i korisna u edukaciji kemije. Jedan od takvih pokusa je i kemijski vrt koji nastaje dodavanjem topljive soli metala u otopinu natrijeva silikata ili nekog drugog aniona s kojim metalni ion daje koloidni gel koji stvara polupropusnu membranu. Rastom kemijskog vrta nastaju cjevčice različitih veličina i oblika koje podsjećaju na stabalca i biljke u vrtu. U članku se opisuje izrada kemijskog vrta upotrebom lako dostupnih kemikalija. Taj pokus na jednostavan način predočuje precipitaciju povezanu s osmozom i izvrsno je edukativno sredstvo. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Visualization of chemical processes is of primary importance in chemistry education. One of such experiments is the chemical garden, which is formed by addition of soluble metal salts in a solution of sodium silicate, or some other anion that forms a colloid gel with a metal ion. Gel forms tubular semi-permeable membranes, which morphologically resemble garden plants. This paper describes preparation of a chemical garden with easily obtainable chemicals. This simple experiment visualizes osmosis-related precipitation and is a very convenient teaching tool. This work is licensed under a Creative Commons Attribution 4.0 International License

Complexation of Oxonium and Ammonium Ions by Lower-rim Calix[4]arene Amino Acid Derivatives

Complexation of oxonium and ammonium cations with two calix4arene amino acid derivatives, namely 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis-(O-methyl-D-α-phenylglycylcarbonylmethoxy)-calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-26,28,25,27-(O-methyl-L-leucylcarbonylmethoxy)calix[4]¬arene (2), in acetonitrile and methanol was studied by means of spectrophotometric and calorimetric titrations at 25 °C. The classical molecular dynamics simulations of the macrocycles and the corresponding complexes with NH4+ and H3O+ were carried out in order to investigate their possible structures in solution. The examined calix[4]arene derivatives were shown to be rather efficient binders for H3O+ cation and moderately efficient for NH4+ in acetonitrile, whereas the complexation of these cations in methanol could not be observed. The structures of the complexes obtained by means of molecular dynamics simulations suggested the involvement of ether and carbonyl oxygen atoms in the complexation of both NH4+ and H3O+. An inclusion of an acetonitrile molecule into the hydrophobic cavity of the free and complexed ligands was observed as well. The difference in binding affinities of 1 and 2 towards NH4+ and H3O+ ions could be explained by taking into account cation solvation, difference in their size and in the strength of hydrogen bonding between cations and the ligand binding sites. (doi: 10.5562/cca2172

Elemental and structural analysis of imapct melt-rocks and glass spherules

Elementni i mineralni sastav uzoraka stijena za koje se pretpostavljalo da su nastale iz impaktnih taljevina, analizirani su metodama TXRF, ICP-AES, PIXE i XRD, a staklene sferule i mikroskopske čestice analizirane su metodom :-PIXE. Za morfološku karakterizaciju površine i elementni sastav uzoraka u mikro-mjerilu korištena je metoda SEM-EDS. Analitičke metode TXRF, ICP-AES i PIXE primijenjene na istim uzorcima dale su usporedive rezultate. Elementne analize uzoraka stijena s otoka Krka, Raba i Cresa pokazale su da uzorci imaju heterogeni sastav i da nisu vulkanskog ni antropogenog porijekla. Elementni sastav analiziranih uzoraka ukazuje da su izvorišne stijene bile po sastavu slične lesu, te da bi mogli biti impaktno staklo iz predložene impaktne strukture na otoku Krku. Sferule permske starosti koje su po prvi put nađene, mogle su nastati uslijed impakta u današnjoj južnoj Kini. Sferule i mikrotektiti eocenske starosti vjerojatno su distalni izbačaj iz kratera Popigai (Rusija) i impaktne strukture Chesapeake Bay (SAD), dok su sferule miocenske starosti vjerojatno distalni izbačaj iz kratera Ries (Njemačka). Sferule pleistocenske starosti mogu potjecati iz predložene impaktne strukture na otoku Krku na što ukazuje njihov elementni sastav.Elemental and mineral compositions of suspected impact glass samples were analysed by TXRF, ICP-AES, PIXE and XRD methods. Glass spherules and microscopic particles were analysed by :-PIXE method. For morphological characterization of surface and elemental composition on micro-scale SEM-EDS method was used. Analytical methods TXRF, ICP-AES and PIXE applied on the same samples gave comparable results. The analyses of rock samples from Krk, Rab and Cres Islands documented their heterogeneous composition and denied their volcanic or anthropogenic origin. Elemental composition of analysed samples indicates their origin from rocks similar to loess by chemical composition and that they could represent impact glass from proposed impact structure on Krk Island. Spherules of Permian age, first reported herein, could originate from an unknown impact crater located somewhere in today's South China. Spherules and microtektites of Eocene age could be distal ejecta from Popigai crater (Russia) and Chesapeake Bay impact structure (USA), whereas spherules of Miocene age could originate from the Ries crater (Germany). Spherules of Pleistocene age probably originated from the proposed Krk impact structure as suggested by their elemental composition

Elemental and structural analysis of imapct melt-rocks and glass spherules

Elementni i mineralni sastav uzoraka stijena za koje se pretpostavljalo da su nastale iz impaktnih taljevina, analizirani su metodama TXRF, ICP-AES, PIXE i XRD, a staklene sferule i mikroskopske čestice analizirane su metodom :-PIXE. Za morfološku karakterizaciju površine i elementni sastav uzoraka u mikro-mjerilu korištena je metoda SEM-EDS. Analitičke metode TXRF, ICP-AES i PIXE primijenjene na istim uzorcima dale su usporedive rezultate. Elementne analize uzoraka stijena s otoka Krka, Raba i Cresa pokazale su da uzorci imaju heterogeni sastav i da nisu vulkanskog ni antropogenog porijekla. Elementni sastav analiziranih uzoraka ukazuje da su izvorišne stijene bile po sastavu slične lesu, te da bi mogli biti impaktno staklo iz predložene impaktne strukture na otoku Krku. Sferule permske starosti koje su po prvi put nađene, mogle su nastati uslijed impakta u današnjoj južnoj Kini. Sferule i mikrotektiti eocenske starosti vjerojatno su distalni izbačaj iz kratera Popigai (Rusija) i impaktne strukture Chesapeake Bay (SAD), dok su sferule miocenske starosti vjerojatno distalni izbačaj iz kratera Ries (Njemačka). Sferule pleistocenske starosti mogu potjecati iz predložene impaktne strukture na otoku Krku na što ukazuje njihov elementni sastav.Elemental and mineral compositions of suspected impact glass samples were analysed by TXRF, ICP-AES, PIXE and XRD methods. Glass spherules and microscopic particles were analysed by :-PIXE method. For morphological characterization of surface and elemental composition on micro-scale SEM-EDS method was used. Analytical methods TXRF, ICP-AES and PIXE applied on the same samples gave comparable results. The analyses of rock samples from Krk, Rab and Cres Islands documented their heterogeneous composition and denied their volcanic or anthropogenic origin. Elemental composition of analysed samples indicates their origin from rocks similar to loess by chemical composition and that they could represent impact glass from proposed impact structure on Krk Island. Spherules of Permian age, first reported herein, could originate from an unknown impact crater located somewhere in today's South China. Spherules and microtektites of Eocene age could be distal ejecta from Popigai crater (Russia) and Chesapeake Bay impact structure (USA), whereas spherules of Miocene age could originate from the Ries crater (Germany). Spherules of Pleistocene age probably originated from the proposed Krk impact structure as suggested by their elemental composition

Elemental and structural analysis of imapct melt-rocks and glass spherules

Elementni i mineralni sastav uzoraka stijena za koje se pretpostavljalo da su nastale iz impaktnih taljevina, analizirani su metodama TXRF, ICP-AES, PIXE i XRD, a staklene sferule i mikroskopske čestice analizirane su metodom :-PIXE. Za morfološku karakterizaciju površine i elementni sastav uzoraka u mikro-mjerilu korištena je metoda SEM-EDS. Analitičke metode TXRF, ICP-AES i PIXE primijenjene na istim uzorcima dale su usporedive rezultate. Elementne analize uzoraka stijena s otoka Krka, Raba i Cresa pokazale su da uzorci imaju heterogeni sastav i da nisu vulkanskog ni antropogenog porijekla. Elementni sastav analiziranih uzoraka ukazuje da su izvorišne stijene bile po sastavu slične lesu, te da bi mogli biti impaktno staklo iz predložene impaktne strukture na otoku Krku. Sferule permske starosti koje su po prvi put nađene, mogle su nastati uslijed impakta u današnjoj južnoj Kini. Sferule i mikrotektiti eocenske starosti vjerojatno su distalni izbačaj iz kratera Popigai (Rusija) i impaktne strukture Chesapeake Bay (SAD), dok su sferule miocenske starosti vjerojatno distalni izbačaj iz kratera Ries (Njemačka). Sferule pleistocenske starosti mogu potjecati iz predložene impaktne strukture na otoku Krku na što ukazuje njihov elementni sastav.Elemental and mineral compositions of suspected impact glass samples were analysed by TXRF, ICP-AES, PIXE and XRD methods. Glass spherules and microscopic particles were analysed by :-PIXE method. For morphological characterization of surface and elemental composition on micro-scale SEM-EDS method was used. Analytical methods TXRF, ICP-AES and PIXE applied on the same samples gave comparable results. The analyses of rock samples from Krk, Rab and Cres Islands documented their heterogeneous composition and denied their volcanic or anthropogenic origin. Elemental composition of analysed samples indicates their origin from rocks similar to loess by chemical composition and that they could represent impact glass from proposed impact structure on Krk Island. Spherules of Permian age, first reported herein, could originate from an unknown impact crater located somewhere in today's South China. Spherules and microtektites of Eocene age could be distal ejecta from Popigai crater (Russia) and Chesapeake Bay impact structure (USA), whereas spherules of Miocene age could originate from the Ries crater (Germany). Spherules of Pleistocene age probably originated from the proposed Krk impact structure as suggested by their elemental composition