Barium nitrate, an inorganic compound with the chemical formula \(\text{Ba}(\text{NO}_3)_2\), is highly soluble in water. This white, crystalline substance is an ionic salt composed of positively and negatively charged ions. When placed in water, this compound readily dissolves, forming a clear, colorless solution. This high degree of water solubility influences its behavior and applications in chemistry and industry.
The Rule That Makes It Soluble
The solubility of ionic compounds in water is generally governed by a set of predictable guidelines known as solubility rules. The determining factor for \(\text{Ba}(\text{NO}_3)_2\)‘s solubility is the presence of the nitrate ion (\(\text{NO}_3^-\)). A fundamental solubility rule states that all compounds containing the nitrate ion are soluble in water, without exception.
This inherent tendency of the nitrate anion to dissolve overrides any potential insolubility from the accompanying cation. While many other barium compounds, such as barium sulfate (\(\text{BaSO}_4\)), are notoriously insoluble, the barium ion (\(\text{Ba}^{2+}\)) cannot prevent the nitrate salt from dissolving. This ensures that barium nitrate is classified as a highly soluble salt.
What Happens When It Dissolves
The physical process that occurs when barium nitrate dissolves is called dissociation. When the solid \(\text{Ba}(\text{NO}_3)_2\) crystals contact water, the polar water molecules begin to pull the compound’s ions apart. The water molecules effectively overcome the electrostatic attraction holding the ions together in the crystal lattice.
Each formula unit separates completely into one positively charged barium ion (\(\text{Ba}^{2+}\)) and two negatively charged nitrate ions (\(\text{NO}_3^-\)). Once separated, the water molecules surround and stabilize these individual ions in a process called hydration or solvation.
The resulting liquid is an electrolyte because the dissolved compound exists as mobile, charged particles in the solution. The presence of these freely moving \(\text{Ba}^{2+}\) and \(\text{NO}_3^-\) ions allows the solution to conduct an electrical current.
Common Applications
The high solubility of barium nitrate makes it valuable in various practical and industrial settings. One of its most recognized uses is in pyrotechnics, where it acts as an oxidizer and a colorant. When heated, the compound produces the brilliant, distinct green color characteristic of many fireworks and signal flares.
In the laboratory, the compound is frequently used as a chemical reagent for precipitation reactions. Because it is highly soluble, barium nitrate solution is an ideal source of \(\text{Ba}^{2+}\) ions that can be added to a solution containing another ion, such as sulfate (\(\text{SO}_4^{2-}\)), to intentionally form an insoluble product. The reaction between soluble barium nitrate and a soluble sulfate salt immediately produces a white precipitate of insoluble barium sulfate, a common test for the presence of sulfate ions.
The high solubility of barium nitrate, however, also contributes to its toxicity. Since it dissolves so readily in water, it is easily absorbed into the body if ingested or inhaled, allowing the toxic barium ions to enter the bloodstream quickly. This characteristic necessitates careful handling. In cases of accidental poisoning, soluble sulfate salts are sometimes administered as a first aid measure to precipitate the barium into the harmless, insoluble barium sulfate within the gastrointestinal tract.