Why Does Water Dissolve Salt
When stirring table salt into water, the visible white crystals disappear into a clear liquid. This highlights waters capability to break down the structure of solid salts. The central question is how liquid water molecules overcome the powerful internal forces holding the salt together.
When salt is mixed with water, the salt dissolves because the covalent bonds of water are stronger than the ionic bonds in the salt molecules. To understand why salt dissolves in water, we must first understand why water is such a powerful solvent. Water molecules (HO) are polar.
This means that while the molecule as a whole is electrically neutral, its electrons are not evenly distributed. Salt (sodium chloride) is made from positive sodium ions bonded to negative chloride ions. Water can dissolve salt because the positive part of water molecules attracts the negative chloride ions, and the negative part of water molecules attracts the positive sodium ions.
Salt dissolves in water due to the polar nature of both substances. Water is a polar molecule, which means it has a slightly positive end and a slightly negative end. Salt is also a polar molecule, because it contains both positively and negatively charged ions.
The dissolution of salt in water is driven by a favorable energy balance. Breaking the ionic bonds within the salt crystal requires an input of energy, called lattice energy. We will first examine the process that occurs when an ionic compound such as table salt (sodium chloride) dissolves in water.
Water molecules move about continuously due to their kinetic energy. When a salt is added to water, it dissolves into its component molecules until as many salt ions as the water can hold are floating around the hydrogen and oxygen molecules. Salt dissolves in water because water molecules are electrically lopsided, with a positive side and a negative side, and they use that imbalance to pry apart the charged particles that hold a salt crystal together.
Its essentially a tug-of-war between the water and the crystal, and water wins. When salt dissolves in water, the sodium and chloride ions become dispersed throughout the water, resulting in a homogeneous solution. This process is facilitated by the attractive forces between the polar water molecules and the charged salt ions.
