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.
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.
Staklo, od Antike do svemirskog doba Marina Čalogović; Tihomir Marjanac
Kemija u industriji; časopis kemičara i tehnologa Jugoslavije,
01/2022, Letnik:
71, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
Staklo je materijal koji se upotrebljava još od Antike pa sve do danas, ali je razvojem tehnologije postalo dostupno svima i sveprisutno je u industriji. Za proizvodnju stakla važan je sastav ...sirovina, a svojstva stakla ovise i o procesu proizvodnje. U članku je opisan proces proizvodnje stakla kroz povijest i razvoj novih vrsta stakla s boljim svojstvima. Također, uspoređeno je antropogeno s prirodnim staklima kao što su opsidijani i tektiti. Opisana su stakla koja se upotrebljavaju za izradu velikih teleskopa i u svemirskoj tehnologiji. U nastavnom dijelu opisani su jednostavni pokusi koji se mogu napraviti u učionici u sklopu STEM-orijentirane nastave.
Staklo je materijal koji se upotrebljava još od Antike pa sve do danas, ali je razvojem tehnologije postalo dostupno svima i sveprisutno je u industriji. Za proizvodnju stakla važan je sastav ...sirovina, a svojstva stakla ovise i o procesu proizvodnje. U članku je opisan proces proizvodnje stakla kroz povijest i razvoj novih vrsta stakla s boljim svojstvima. Također, uspoređeno je antropogeno s prirodnim staklima kao što su opsidijani i tektiti. Opisana su stakla koja se upotrebljavaju za izradu velikih teleskopa i u svemirskoj tehnologiji. U nastavnom dijelu opisani su jednostavni pokusi koji se mogu napraviti u učionici u sklopu STEM-orijentirane nastave.
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Chemical composition of melt-rocks from several localities around proposed post-Eocene Krk impact structure in Croatian carbonate (a.k.a. External) Dinarides was analyzed by three spectroscopic ...methods to decipher their source lithology. The utilized spectroscopic methods were ICP-AES, TXRF and PIXE+EBS, and their applicability for the analysis of melt-rocks was tested. The three analytical techniques provided comparable elemental compositions of the analyzed samples, but PIXE+EBS proved the best as undestructive method with easier and faster sample preparation, and reliable and consistent results. The obtained results show high discrepancy in chemical composition of analyzed melt-rocks with published data on Eocene Adriatic flysch, but close affinity with Pleistocene Adriatic loess. Consequently, the parent material of melt-rocks was probably loess, which might indicate the approximate age of the melt formation as Pleistocene.
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)calix4arene (1) and 5,11,17,23-tetra-tert-butyl-26,28,25,27-(O-methyl-L- leucylcarbonylmethoxy)calix4-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 NH.sub.4.sup.+ and H.sub.3O.sup.+ were carried out in order to investigate their possible structures in solution. The examined calix4arene derivatives were shown to be rather efficient binders for H.sub.3O.sup.+ cation and moderately efficient for NH.sub.4.sup.+ 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 NH.sub.4.sup.+ and H.sub.3O.sup.+. 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 NH.sub.4.sup.+ and H.sub.3O.sup.+ 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) Keywords: calixarenes, oxonium cation, ammonium cation, complexation, solvation, microcalorimetry, UV spectrometry, molecular dynamics
The setting processes in the commercial glass ionomer cement (Fuji IX Fast) and resin modified glass ionomer cement (Fuji II LC) were investigated by the dielectric spectroscopy. The changes in the ...real and imaginary parts of the dielectric permittivity ε*(ω) as well as dielectric loss (tan δ) with time for Fuji IX Fast show several distinct regions which are related to the different stages of the acid–base reaction. Interestingly, the first stage that lasts for approximately 12 min terminates with a sharp decrease in dielectric parameters which is most probably related to the instantaneous (micro)fracturing of the sample due to a rapid build–up of the shrinkage stress. On the other hand, evolution of the dielectric properties during the setting of Fuji II LC indicates fast reaction in the initial stage (within few minutes) followed by the slow gradual change as a result of the competing nature of the acid–base reaction and light‐activated polymerization.
Novel zinc(II) coordination compounds with imidazole (Im) and 2-methylimidazole (2-MeIm) were prepared and characterized: ZnX2(Im)2 (X = Cl (1a), Br (1b), I (1c)) and ZnX2(2-MeIm)2 (X = Cl (2a), Br ...(2b), I (2c)). Coordination compounds 1a–c were prepared mechanochemically by neat grinding while 2a–c were prepared by solution synthesis. The complexes were characterized by FT-IR and NMR spectroscopy and by powder X-ray diffraction. Crystal and molecular structures were determined by the single crystal X-ray diffraction. The characteristic of all structures is a distorted tetrahedral coordination of zinc consisting of two halide atoms and two nitrogen atoms from the imidazole (or 2-methylimidazole) ligand. Molecules in 1a–c are interconnected by hydrogen bonds into 3D structures. Structures of 1b and 1c were found to have similar unit cells and similar crystal packing and hydrogen bonding. Introduction of the 2-methylimidazole substituent introduced disorder in the crystal structures of 2a–c. Because of the very small size of the crystals data were collected by synchrotron radiation. For the disordered 2a,2b and 2c fixed geometry was used in refining of the structures. Crystal structures of 2a–c are characterized by chains of molecules connected by hydrogen bonds of the type N–H⋅⋅⋅X, with weak π⋅⋅⋅π and van der Waals interactions between the chains. The QTAIM, RDG and NCI computational analysis of 1a and 2a–c confirmed the presence of weak attractive intermolecular interactions that can be attributed to weak N–H⋅⋅⋅X and van der Waals interactions.
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Zn(II) coordination compounds; Imidazole; 2-Methylimidazole; Crystal structure; Neat grinding; Intermolecular interactions; Computational analysis.
Cyclic dinuclear molybdenum(vi) complexes MoO2(L1–3)2 (1, 2-α, 2-β and 3) were synthesized through the use of coordination-driven self-assembly of a MoO22+ core and 4-aminobenzoylhydrazone ligands ...(salicylaldehyde (H2L1), 3-methoxysalicylaldehyde (H2L2) or 4-methoxysalicylaldehyde 4-aminobenzoylhydrazone (H2L3)). Their X-ray diffraction (XRD) analysis revealed that these types of ligands could serve as organic linkers for cis-octahedral complexes containing a MoO22+ core. Mononuclear complexes MoO2(L1–3)(MeOH) (1a–3a) and MoO2(L1–3)(EtOH) (1b, 2b-α, 2b-β and 3b) were also obtained. In the presence of strong donors, such as dmf, ligand substitution occurred and the structures of 1–3 changed into MoO2(L1)(dmf) (1c), MoO2(L2)(dmf) (2c) and MoO2(L3)(H2O)·dmf (3c·dmf), respectively. The dioxidomolybdenum(vi) complexes were tested for catalytic epoxidation of cyclooctene under eco-friendly reaction conditions by using aqueous tert-butyl hydroperoxide (TBHP) as an oxidant without the addition of an organic solvent. The present study showed much better activity of the dinuclear catalysts than the mononuclear ones due to the weak donor properties of the amino group and high geometric constraints occurring in such small sized self-assembled systems as confirmed by density functional theory calculations.
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