How Does Water Act As a Solvent?

The small size and polarity of water molecules enable them to surround and dissolve solute species. Water molecules are partially negative on the oxygen end and partially positive on the hydrogen ends. Negative species are surrounded hydrogen-first, while positive species are surrounded oxygen-first.

The stronger the attraction between the water molecules and the dissolving species, the better the solute dissolves in water. Ionic salts that completely dissociate into positive and negative ions, such as sodium chloride, have a high solubility in water. Other polar substances that are soluble in water include acids and alcohols. Nonpolar substances, such as fats and oils, are generally water-insoluble.

The polar nature of water arises from the strength of the oxygen ion to attract the two covalent electrons between it and the two contributing hydrogen atoms more strongly than these two hydrogens. The electrons spend more time around the oxygen atom than around the hydrogen atoms, leading to the accumulation of a partial negative and partial positive charge respectively.

When solid grains of table salt are placed in water, the water molecules are immediately attracted to the positive and negative sodium and chlorine ions at the surface of the grains respectively. These water molecules disrupt the ionic bonds keeping these surface sodium and chlorine ions together, causing them to leave the bulk lattice of the grain.