Silver halides are compounds formed by halogens and silver, and all except for silver fluoride are precipitates. Silver fluoride and silver chloride are white, silver bromide is light yellow, and silver iodide is yellow. Except for silver iodide, which has a zinc sulfide (ZnS) type crystal lattice, all other silver halides belong to the sodium chloride (NaCl) type crystal lattice. Silver fluoride is soluble in water, while the others are slightly soluble in water, with solubility decreasing in the order of chlorine to iodine. Silver fluoride is an ionic compound, while the others are covalent compounds. Today, we will discuss the properties and uses of Silver fluoride and Silver chloride.
Silver fluoride, with a CAS number of 7775-41-9, has a molecular formula of AgF and a molecular weight of 126.87. It is a white crystal at room temperature with a melting point of ≥300℃(lit.) and a boiling point of 1150℃. It is highly soluble in water under standard conditions, with a solubility of 182 g/100 mL (15.5 ℃). Its chemical bond is an ionic bond, which distinguishes it from other silver halides. The crystal structure is similar to that of sodium chloride and the same as that of silver chloride/bromide.
Presentation: The preparation method involves dissolving Ag2O in hydrogen fluoride to obtain AgF: Ag2O + 2HF == 2AgF + H2O. The solution is then evaporated in a water bath, transferred to a sand bath, and stirred with a platinum spoon until dry. The purity of the resulting product is 92% to 95% (containing 5% to 8% Ag2O), and the entire synthesis process should carry out in the dark.
But long-term exposure to large amounts of silver fluoride can lead to chronic fluorosis while swallowing silver fluoride can cause acute fluorosis and death.
High-purity silver fluoride is an important optical material, especially high-purity silver fluoride crystals, which have many excellent properties and can serve as low-refractive-index materials in photonic crystals. In addition, silver fluoride is also often used in dental, semiconductor, and other industries.
Silver chloride, with a CAS number of 7783-90-6, has a molecular formula of AgCl and a molecular weight of 143.32. It is a photosensitive white powder that darkens under light (turning purple and gradually black). Its melting point is 455℃, its boiling point is 1550℃, its relative density is 5.56, and its crystal structure is the same as NaCl.
It is soluble in concentrated ammonia water, thiosulfate solution, and boiling concentrated hydrochloric acid with cyanide; it is not soluble in organic solvents, water, ethanol, or dilute acids.
The preparing silver chloride process involves adding either hydrochloric acid or sodium chloride solution to a silver nitrate solution, adding them to a hot silver nitrate solution. The entire process should carry out in a darkroom with red light.
①Silver chloride is commonly used in the laboratory to determine the silver content of samples due to its low solubility.
②It applies to those not highly sensitive photographic films, plates, and papers.
③In electrochemistry, silver-chloride reference electrodes are significant, as they are not polarized and can provide accurate data. Due to the decreasing use of mercury in laboratories, Ag/AgCl electrodes are becoming more common.
Silver fluoride (AgF) and silver chloride (AgCl) are white, either. However, the solubility of silver fluoride is much higher than that of AgCl. AgF is soluble in water, while AgCl is only slightly soluble. And AgF is an ionic compound, while AgCl is a covalent compound. This difference in chemical nature affects their reactivity with other substances. Then, Due to their unique properties, silver halides are used in various applications. Silver fluoride utilizes more in dentistry as an antibacterial agent.
In conclusion, silver fluoride and silver chloride are two important silver halides with unique properties and applications. While both compounds are white in color, their solubility and crystal structure differ significantly. AgF is an ionic compound and is more soluble than AgCl, which is a covalent compound. AgF is also a strong oxidant, while AgCl is relatively inert. These differences in properties make them suitable for different applications.