Problem 2 - Chemistry in 30 days

Question

The sulphides of which one of the following groups of elements are soluble in yellow ammonium sulphide? (a) As, Sb and Sn (b) As, \(\mathrm{Cd}\) and \(\mathrm{Sn}\) (c) Cd. \(\mathrm{Cu}\) and \(\mathrm{Bi}\) (d) \(\mathrm{Hg}, \mathrm{Cu}\) and \(\mathrm{Cd}\)

Step-by-Step Solution

Answer

Sulphides of As, Sb, and Sn are soluble in yellow ammonium sulphide (Option a).

Step 1: Understanding the Question

The question asks which group of elements has sulphides that are soluble in yellow ammonium sulphide. The options provided list different groups of elements, and we must determine which group has sulphides that will dissolve.

Step 2: Properties of Yellow Ammonium Sulphide

Yellow ammonium sulphide, or ammonium polysulphide, is known for reacting with certain metal sulphides to form soluble complexes, specifically with the sulphides of arsenic (As), antimony (Sb), and tin (Sn).

Step 3: Evaluate Each Option

Assess each group listed in the options: - Option (a) includes As, Sb, and Sn. - Option (b) includes As, Cd, and Sn. - Option (c) includes Cd, Cu, and Bi. - Option (d) includes Hg, Cu, and Cd. The correct group whose sulphides are soluble are known to include As, Sb, and Sn.

Step 4: Conclusion on Solubility

Based on the behavior of yellow ammonium sulphide, the correct answer is the group that includes As, Sb, and Sn, because sulphides of these elements are known to dissolve in yellow ammonium sulphide.

Key Concepts

Metal Sulphides Solubility

Metal sulphides are compounds formed by combining metal ions with sulphur ions. Their solubility in solutions is quite varied, depending on the metal involved. For example, the sulphides of metals like lead and mercury are typically insoluble in water. However, they can dissolve in certain other reactive solutions. Solubility can be influenced by multiple factors, including:

• The specific type of metal ion.
• The type of solution used.
• The pH level of the solution.

Understanding which metal sulphides are soluble in specific conditions is important in many chemical analysis and separation processes. In the context of the exercise, the focus was on sulphides that dissolve in ammonium sulphide. By considering the special reactivity of certain sulphides with ammonium sulphide, it becomes clear why some group of metals can form soluble complexes while others cannot.

Ammonium Sulphide Reactions

Ammonium sulphide complex allows for interesting reactions with metal sulphides. Notably, it reacts with certain metal sulphides to form soluble complexes. Typically, yellow ammonium sulphide is an aqueous solution containing ammonia and sulphur, and often called ammonium polysulphide. Why is it important? * It is effective in selective dissolution of certain metal sulphides. * Key in separation techniques for metallurgy and chemistry. When reacting with arsenic (As), antimony (Sb), and tin (Sn), their sulphides dissolve. This is due to the formation of soluble thio-complexes. The comprehension of such reactions is crucial in qualitative analysis where the separation of ions is a fundamental step.

Element Groups Solubility

The concept of element group solubility involves understanding which elements' compounds dissolve in different solutions. Different groups of elements show varied solubility patterns based on their chemical properties. Certain rules, often taught in inorganic chemistry, can be applied to predict solubility trends:

• Elements like silver, lead, and mercury tend to form insoluble sulphides.
• Metals from the transition group have varied solubility depending on other factors such as temperature and pH.

For the exercise, solubility in ammonium sulphide solution was specific to elements like As, Sb, and Sn due to their unique ability to form soluble complexes. Understanding these group trends helps in predicting the behavior of elements in various chemical processes.

Sulphide Complexes

Inorganic chemistry delves into the formation of complex ions, including sulphide complexes, which are compounds featuring a central metal atom bonded to more than one sulphide ion. The complexity and stability of these complexes depend on the metal and its environment. Here are some principles: * Complexes often exhibit stability due to chelation or multidentate ligand binding. * The formation of such complexes can be influenced by the type of ligands. Soluble sulphide complexes, like those formed with arsenic, antimony, and tin in ammonium sulphide, are formed when sulphide ions create bonds with metal cations, making them more soluble. This concept is essential in understanding how certain processes, such as metal refining and chemical analysis, are carried out. By leveraging their solubility properties, chemists can effectively separate or identify components within a mixture.