Solubility and wetting of substances in water [closed]








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We have seen that, when we pour salt in water then it gets dissolved, that means it is soluble in water. But when we pour sand into water then it doesn't dissolve in water, that means it is insoluble, but still sand gets wet. But there are certain substances which doesn't get wet by water for example, sulfur particles don't get wet by water but wet in oil, as I was studying about froth floatation method.


My question is that:


* What is the difference between solubility and wetting in water ?
* What is the reason that the sulfur particle doesn't get wet by water?




Polar/hydrophilic soluble substances get dissolved, like table salt or sugar.


Polar/hydrophilic insoluble substances get wet, as they attract water, like sand, or limestone.


Nonpolar/hydrophobic insoluble substances do not get wet, as they repulse water, like wax, teflon or silanized glass.


 2

The water molecules undergo a sort of attraction between them. This attraction is due to $\ce{H}$ atoms being attracted by the oxygen atoms of neighboring water molecules. At the surface of the water this attraction produces a sort of "skin" due to the attraction of the molecules between them. If a solid is touching this surface, it may produce a similar attraction between its molecules and water. This is the case when the outer part of the solid contains the same $\ce{H}$ and $\ce{O}$ atoms as water. In that case, the attraction between water and these foreign atoms allow water to wet the solid. And even to "climb" a couple of millimeters inside the stuff. 


Sulfur has no $\ce{H}$ or $\ce{O}$ atoms. It cannot make bonds with water. So water molecules on the water surface refuse to break their bonds for wetting this foreign solids. 


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