LHcheM
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2 chemistry problems
These are simple chemistry problems, but I can't find any explanation web, so someone please help me!
1. Why the liquid range of aluminium is so large compared to Mg and Na?
2. Why some substances shows negative solubility coefficient with temperature? (ie more insoluble in hot water, soluble in cold water eg Nd2(SO4)3 )
Thanks!!!
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neptunium
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right underneath Al we find Gallium on the periodic table, and again Ga has one of the longest liquid phase of all the elements.
i`ve red something about the vapor preassure of this metal ( and Al) they keep a high viscosity when liquid i have a few ideas as of why but i m gonna
let the forum go on for a while
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neptunium
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either nobody is interested or no one has a clue so far....
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AJKOER
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Quote: Originally posted by LHcheM  | These are simple chemistry problems, but I can't find any explanation web, so someone please help me!
2. Why some substances shows negative solubility coefficient with temperature? (ie more insoluble in hot water, soluble in cold water eg Nd2(SO4)3 )
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One possible explanation is that upon reaction with water at different temperatures, there could be more significant progress in a
hydrolysis/ionization reaction, or the formation/dissolution of complexes or bonds. In any of these cases, we are not looking at the solubility of
truly the same 'substance' either from a chemical or physical perspective. Hence, there could be observed a seeming reversal in solubility, which is
actually the solubility of the new compound.
[Edited on 4-1-2012 by AJKOER]
[Edited on 4-1-2012 by AJKOER]
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Ozone
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We see inverse solubility of calcium salts (especially Ca(OH)2 in the sugar industry) every day, a bit of information is given here:
http://books.google.com/books?id=5px8GzscIRsC&pg=PA104&a...
For salts like these, there is a negative entropy of solution (see also "hydrophobic effect"): Hopkins, H.P. and Wulff, C.A. (1965).
The Solution Thermochemistry of Polyvalent Electrolytes. I. Calcium Hydroxide. J. Phys. Chem. 69 (1), pp. 6-8.
DH(sol): -4290 cal/mol
DS(sol): -38.2 cal/mol.K
Because DG = DH - TDS, DG(298K) = +7094 cal/mol. (30 kJ/mol).
This means that solution is disfavored (both enthalpic and entropic factors), and becomes even less favorable as T increases. For example, NaCl, which
is spontaneously soluble in water, DG is negative.
This is (at least in some cases) because "the entropy of a system is lowered when the solution forms because solvent molecules form cagelike
structures around the solute molecules." (http://books.google.com/books?id=4R6hb1OIMRUC&pg=PA327&a...).
My stab at it, anyway,
O3
Attachment: Hopkins and Wulff 1965 CaOH2.pdf (278kB)
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Attachment: Entropy and Gibbs Energy_ch15_student.pdf (198kB)
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Attachment: Feakins et al 1989 Thermo of solutions.pdf (1.1MB)
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-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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