What happens if liquid and solid mix?

Answer 1

Any number of things, depending on what the substances are. One of the most interesting is a "non-Newtonian fluid" which can be experienced with equal parts of water and cornstarch.

Commonly, a liquid and a solid mixing will be just that - a liquid and a solid mixed (think of rocks in water, or mud. The sand in the mud is still present and water molecules encircle it). Another thing that can happen is you get a solution, i.e. the solid is dissolved in the liquid. This happens with salt and water, for example. The solid salt breaks down into its respective ions (in this case, a sodium cation Na+ and a chloride anion Cl-) which float around the water molecules at a sub-microscopic level and what we are left with is salt water!

---------------------------------------------------------------

To be really precise is quite difficult since the variety of possible phenomena is huge. Some interesting possibilities related to everyday life can be evidenced if the liquid is composed by polar molecules, like water or common alcohol (ethane).

If we put a ionic solid (like common salt) in a polar liquid, liquid particles attach to the ions constituting the solid and, if temperature is sufficiently high, detach them from the solid body and surround them crating a sort of liquid particle shell all around every ion (this phenomenon is called hydration in the case of water). This is the mechanism causing polar solvents like water to dissolve ionic or polar solids like salt.

If a polar solvent is put in contact with a non polar solid this phenomenon cannot happen since the solid particles are not sensible to electromagnetic forces and the only way the liquid has to detach particles from the solid body is by collisions, that is a quite inefficient method, unless the temperature is really very high. Thus non polar solids generally do not dissolve effectively in polar liquids.

If the solid do not dissolve in the liquid, it is possible that the liquid wets the solid surface or not. In the first case liquid droplets on the solid surface are quite shallow, tending to be flat. In the second case droplets retain an almost spherical shape, even if the contact surface with the solid generally do not degenerate to a single point. The subjective effect is that, if the liquid do not wet the solid, after the contact with the liquid, the solid surface do not retain any liquid particle so that is appears to be dry. If the liquid wets the solid, a few liquid particles remains attached to the solid surface and it appears wet after the extraction of the solid body from the macroscopic liquid mass.

Another interesting effect happening when a solid body is immersed into a liquid that do not dissolve it is the presence of a force, called Archimede's force, opposing the gravity and tending to push the solid upward. It is essentially due to the interaction between the solid and the liquid particle while the solid during immersion substitutes part of the liquid body. The Archimede's force intensity is equal to the weight of the liquid mass moved by the solid during its immersion in the liquid and, if the solid density is smaller in average with respect to the liquid one, the solid do not immerse completely in the liquid since immersion stops when the Archimede's force balance the gravity force. This is the principle causing ships to remain on the sea surface.

There are a lot of other phenomena happening when a solid interacts with a liquid, comprising the change of theh liquid characteristics happening when the solid is dissolved by the liquid, comprising the rise of non-Newtonian characteristics cited by the other answerer, that is really a very interesting phenomenon.