Hydrophilic, literally translated into “water-loving”, is the exact opposite of the term hydrophobic. When substances are hydrophilic they have the ability to dissolve in water whereas hydrophobic substances separate from water. Because of water’s polarity, any substance that is polar is also hydrophilic.
Water is considered the solvent of life because it is critically important in all cells, blood, and even plant sap! A solvent is the medium that a substance is dissolved in while a solute is the substance that is being dissolved. Polar and ionic compounds are all hydrophilic.
Salt, being ionic, is a great example of a hydrophilic substance. Salt is composed of sodium and chlorine atoms. The way that their ionic bonds are arranged makes the sodium atom positive charged (Na+) and the chlorine atom negatively charged (Cl-). The NaCl crystal can be any size but the ratio of salt to chlorine atoms is always 1:1. This is similar to H2O molecules- The covalent bond causes the oxygen atom to be slightly more negative and the hydrogen atoms to be slightly more positive.
When salt is mixed with water, the sodium and chlorine atoms dissociate. Na+ becomes surrounded by the O- (negatively charged oxygen atoms) while Cl- becomes surrounded by the H+ (positively charged hydrogen atoms). This is because opposites really do attract. Other good examples of compounds that are hydrophilic include sugar and many proteins.