lthough much of the explanation for why certain substances mix and form
solutions and why others do not is beyond the scope of this class, we
can get a glimpse at why solutions form by taking a look at the
process by which ethanol, C2H5OH, dissolves in
water. Ethanol is actually miscible in water, which means that the two
liquids can be mixed in any proportion without any limit to their
solubility. Much of what we now know about the tendency of particles
to become more dispersed can be used to understand this kind of change
as well.
Picture a layer of ethanol being carefully added to the top of some water (Figure below).
Because the particles of a liquid are moving constantly, some of the
ethanol particles at the boundary between the two liquids will
immediately move into the water, and some of the water molecules will
move into the ethanol. In this process, water-water and
ethanol-ethanol attractions are broken and ethanol-water attractions
are formed. Because both the ethanol and the water are molecular
substances with O−H bonds, the attractions broken between water
molecules and the attractions broken between ethanol molecules are
hydrogen bonds. The attractions that form between the ethanol and
water molecules are also hydrogen bonds (Figure below). There you go
