pkgem

Thanks Mokele! I actually managed to find a colleague who helped me with this but your input has just clarified the my ultimate realisation that strain-to-failure is the same as elongation-at-break. So, many thanks for responding - just the help I needed at just the right time!

Hi, I am doing an assignment for my final project for my Open University Chemisty degree. I am doing it on cellulose bionanocomposites. I'm doing ok with the "normal" chemistry but I am struggling with some of the materials science. Some of the papers I have researched report upon the "strain-to-failure" of the bionanocomposite films they have produced. I know that strain-to-failure measures the amount of strain a solid material can withstand before it "fails", is calculated from measurements gained from stress-strain curves and is expressed as a percentage. What I don't understand is what the percentage is actually measuring - what is it a percentage of? I have performed google searches and looked through the material science books I have to hand but have received no joy. Please can anyone help or advise me? Many thanks, Gemma

Thanks for replying guys

Can anyone tell me the pKa value for tetrahydrofuran (THF)? I know it is the solvent I require for the reaction conditions in my answer and I know it's pKa value is higher than 25. However, it would be nice to know exactly what the pKa is. Please can someone advise me or (even better) direct me to a web-based list of solvents and their corresponding pKa values. Thanks

Hi all, I'm trying to answer an assignment question that asks me to draw and name the isomers of a particular transition-metal complex and then identify the number of chemically inequivalent telluriuim atoms in the isomers. So far, so good except for I'm a little confused with regards to my nomenclature for the transition-metal complex that I have. It's octahedral and contains only two distinct ligands: in other words, it has two sets of three identical ligands. Thus, it fits nicely with the fac/mer system of naming - I can identify that it can have both facial and meridional isomers. What I'm not sure about is whether I can (and should) apply the Cahn-Ingold-Prelog system also. The CIP system for octahedral complexes starts by saying I have to identify the priority 1 ligand - however, as I have sets of identical ligands, I have three priority 1 ligans. So, which do I choose? Or is it unecessary and I only need to apply the fac/mer system? In summary: Can the CIP system be applied for octahedral metal complexes that don't have six non-identical ligands? Any help would be appreciated. It doesn't directly answer my assignment question but it helps me to understand a part of it. So, thanks in advance. Gem

You could try the entry in Wikipedia for paper chromatography: http://en.wikipedia.org/wiki/Paper_chromatography It's short but has links to other chromatography entries. Thin-layer chromatography is very similar to paper and there's a fuller entry for that which gives more details on analysis. A lot of teachers/ tutors etc... don't approve of Wikipedia because it can be edited by anyone so all information may not be accurate. However, if you use your own judgement and be aware that it isn't the same as a textbook then Wikipedia can be a really usefult site. Especially for pointing you in the right direction as opposed to giving you definitive answers. I hope this helps and good luyck with your assignment! Gem

Hi all, I have a question on an assignment that requires me to draw a structure for a transition-metal carbonyl complex [Fe2(CO8]2- (I'm new to this forum and cannot see where to apply super/subscript). To work out the structure, I first need to apply the eighteen electron rule. I have worked out that Fe is in the oxidation state +1 and thus each Fe ion contributes 7 electrons. There are 8 carbonyl ligands supplying a total of 16 electrons, that's eight each to each Fe ion - a total of 15 electrons. I know that the metal can be bonded to itself in these complexes but it there is an Fe-Fe bond then that would only supply one additional electron, taking my total to 16 which falls short of the 18-electron rule by 2. So, either metals can bond multiple times is such complexes (such as a triple bond between the Fe ions which doesn't seem right to me at all) or is it due to bridging atoms in the complex - do bridging atoms supply less electrons to the metal in the complex? Please can anyone help? Many thanks, Gem