Strontium chloride (\(\text{SrCl}_2\)) is an inorganic salt that appears as a white crystalline solid and is highly soluble in water. Composed of one strontium ion and two chloride ions, this compound readily dissolves when introduced to a water medium. Its nature as an ionic salt dictates a strong affinity for water molecules, making dissolution a straightforward and efficient process. Its high solubility underpins many of its practical uses in various industries.
The Chemistry of Dissolving
Strontium chloride is classified as an ionic compound, meaning it consists of positively charged strontium ions (\(\text{Sr}^{2+}\)) and negatively charged chloride ions (\(\text{Cl}^-\)) held together by strong electrostatic forces in a crystal lattice structure. Water is a polar solvent, characterized by its molecular structure where oxygen holds a partial negative charge and the hydrogen atoms hold partial positive charges. This polarity enables water to act as a powerful solvent for ionic substances, following the chemical principle of “like dissolves like.”
When \(\text{SrCl}_2\) is placed in water, the polar water molecules surround the solid crystal, pulling the individual ions away from the lattice. The negative ends of the water molecules are attracted to the positive \(\text{Sr}^{2+}\) ions, while the positive ends surround the negative \(\text{Cl}^-\) ions. This process is known as dissociation, where the salt breaks apart into its constituent ions, and hydration, where the separated ions become encased in a shell of water molecules. The resulting solution is an electrolyte, meaning it contains free-moving ions and is capable of conducting an electric current.
Measuring Solubility
Moving from the qualitative understanding that \(\text{SrCl}_2\) dissolves to a quantitative measure reveals just how soluble this salt is. At a standard temperature of \(20^{\circ}\text{C}\) (\(68^{\circ}\text{F}\)), approximately \(53.8\) grams of anhydrous strontium chloride can dissolve in \(100\) milliliters of water. This figure indicates a significantly high solubility.
The solubility of strontium chloride is also dependent on temperature, increasing significantly as the water heats up. For example, the hexahydrate form of the salt can reach a solubility of \(206\) grams per \(100\) milliliters of water at \(40^{\circ}\text{C}\). In comparison, a common salt like sodium chloride has a much flatter solubility curve, dissolving at about \(36\) grams per \(100\) milliliters of water at \(20^{\circ}\text{C}\). This difference highlights the substantial capacity of water to dissolve strontium chloride, especially at elevated temperatures.
Practical Significance of Strontium Chloride Solutions
The ability of strontium chloride to form a highly concentrated ionic solution makes it valuable across several applications. One major use is in specialized dental products, particularly desensitizing toothpastes. In these products, the soluble strontium ions work by blocking the microscopic dentinal tubules in the teeth that lead to nerve endings, reducing the transmission of pain signals and minimizing tooth sensitivity.
Strontium chloride is also utilized in pyrotechnics, where its solution properties are leveraged for visual effect. When the salt is incorporated into a pyrotechnic mixture and ignited, the strontium ions emit a characteristic, intense red color to the flame. Furthermore, the radioactive isotope strontium-89 is administered in the form of strontium chloride for certain medical treatments, such as bone cancer therapy, relying on its solubility to be effectively distributed in the body.