Nina Bou
Dissolution is the distribution of a substance in the form of ions or molecules in another substance, a solvent. Dissolution is not a chemical reaction. Oxides with a covalent bond do not partition into another solvent. They can only react with other substances by entering into a chemical reaction. Then their molecules undergo changes.
I largely agree with Yuri in concept, although not entirely in the details. I think the general idea is that dissolution and precipitation/crystallization are 'reversible'. Dissolve sugar in water, evaporate the water, you get the sugar back. It get's a lot trickier if you dissolve gold in aqua regia, put that in a furnace, get the gold back. What we are both really talking about is the strength of the interaction holding the solid together. For strong bonds, 'dissolution' is not really the right concept. For strong bonds it is more a case of 'transformation'. For weak bonds, dissolution is much closer to the right idea. Metal oxide bonds, in general, are very strong.
If you were to pose the question as follows...how can I TRANSFORM insoluble metal oxides into soluble metal species (no longer oxides), then the stock answer would be with acid, and time (a LOT of time), and probably some heat, and some stirring.
Another way is with heat (a LOT of heat) and an oxide scavenger like carbon.
Either way, you have to pay the piper.
Scott Gordon-Wylie
I gave a short answer to a simple question, although it could be lengthened. Your answer sparks a discussion that will be helpful to students. We have divided the concepts of dissolution and chemical reaction. Why then again mislead students with the phrase “you dissolve gold in aqua regia”. This is not a dissolution, but a redox reaction. You replace the term chemical reaction with 'transformation'. Your sentence "For strong bonds, 'dissolution' is not really the right concept" is difficult to understand.
The copper atom is surrounded by four oxygen atoms and has a distorted planar configuration in the elementary crystal lattice. The bonds between the copper atom and oxygen are covalent. This configuration is repeated throughout the copper oxide grain. This elementary crystal lattice cannot be distributed in a solvent (water) with a gain in changing the Gibbs energy. Kitchen salt sodium chloride spontaneously distributes in water to form sodium and chlorine ions, since the system benefits in Gibbs energy compared to the components crystalline salt and water.
Point taken Yuri. It is important to be precise in the language.
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