Answer. Water as Solvent
Water is the universal solvent because it can dissolve almost all the minerals. Its ability to dissolve substances is because of two unique properties of water:
(i) polarity of water molecule;
(ii) exceptional hydrogen bonding ability.
(i) Polar nature of water:
Water molecule has a polar structure, i.e., one end of the molecule is partially positive while the other end is partially negative because of electronegativity difference between oxygen and hydrogen atoms.
All other polar substances are soluble in water, because the positive H8+ end of the substance is attracted by the negative end (O5-) of the water and negative end of the substance is attracted by the positive end (H8+) of the water. The electrostatic attractions among the ions are overcome by the ion-dipole forces of attraction between ion and water molecules. In this way positive and negative ions of the compounds are pulled apart as shown in figure. Ultimately, these oppositely charged ions are surrounded by water molecules, thus separated and kept in solution. For example, most of the salts like NaCl, KC1, Na2SO4, etc., are soluble in water.
Dissolving process of a polar substance in water
On the other hand, many covalent substances like benzene, ether, octane, etc., which do not have polar ends or bonds are not attracted by water molecules. Therefore, non-polar compounds do not dissolve in water.
(ii) Extensive Hydrogen Bonding Ability
Water molecule is composed of oxygen and hydrogen atoms.
Because of two O-H bonds and two lone pairs, one H2O molecule can form hydrogen bonding with four other H2O molecules, which are arranged like tetrahedral around the H2O molecule as shown in Figure. This unique behavior of water enables it to dissolve many polar non-ionic compounds having hydroxyl group (-OH), like alcohols, organic acids, glucose, sugar etc. by forming hydrogen bonds with them.
Hydrogen bonding of water molecule