Universal Solvent Definition

What Is a Universal Solvent in Chemistry?

Water is often called the universal solvent, though it does not dissolve everything.
Water is often called the universal solvent, though it does not dissolve everything. ballyscanlon, Getty Images

Universal Solvent Definition

A universal solvent is a substance that dissolves most chemicals. Water is called the universal solvent because it dissolves more substances than any other solvent. However, no solvent, including water, dissolves every chemical. Typically, "like dissolves like." This mean polar solvents dissolve polar molecules, such as salts. Nonpolar solvents dissolve nonpolar molecules such as fats and other organic compounds.

Why Water Is Called the Universal Solvent

Water dissolves more chemicals than any other solvent because its polar nature gives each molecule a hydophobic (water-fearing) and hydrophilic (water-loving) side. The side of the molecules with two hydrogen atoms has a slight positive electrical charge, while the oxygen atom carries a slight negative charge. The polarization lets water attract many different types of molecules. The strong attraction to ionic molecules, such as sodium chloride or salt, allows water to separate the compound into its ions. Other molecules, such as sucrose or sugar, aren't torn into ions, but disperse evenly in water.

Alkahest as the Universal Solvent

Alkahest (sometimes spelled alcahest) is a hypothetical true universal solvent, capable of dissolving any other substance. Alchemists sought the fabled solvent, as it could dissolve gold and have useful medicinal applications.

The word "alkahest" is believed to have been coined by Paracelsus, who based on the Arabic word "alkali". Paracelsus equated alkahest with the philosopher's stone. His recipe for alkahest included caustic lime, alcohol, and carbonate of potash (potassium carbonate). Paracelsus' recipe could not dissolve everything.

After Paracelsus, alchemist Franciscus van Helmont described the "liquor alkahest", which was a sort of dissolving water that could break any material into its most basic matter. Van Helmont also wrote of "sal alkali", which was a caustic potash solution in alcohol, capable of dissolving many substances. He described mixing sal alkali with olive oil to produce sweet oil, likely glycerol.

Why There Is No Universal Solvent

Alkahest, had it existed, would have posed practical problems. A substance that dissolves all others cannot be stored because the container would be dissolved. Some alchemists, including Philalethes, got around this argument by claiming alkahest would only dissolve material down to its elements. Of course, by this definition, alkahest would be unable to dissolve gold.