MCQ Detailed View

In analytical chemistry, hydrogen sulfide (H₂S) is used to detect and separate metal ions by forming insoluble metal sulfides. When H₂S is passed through solutions containing metal ions, some metals form distinct insoluble sulfides that precipitate, while others do not. This allows chemists to identify and distinguish metal ions in a mixture.

Certain metals, such as Hg²⁺ (mercury) and Pb²⁺ (lead), form sulfides that are very similar in solubility and appearance. Because their sulfides behave almost the same in H₂S, they cannot be distinguished from each other using this method alone. This is why Hg and Pb form the pair that is not distinguished by H₂S.

Other metal pairs can be distinguished because their sulfides differ in solubility. For example, Zn²⁺ and Mn²⁺ form sulfides that are more soluble or distinct in acidic medium, making them distinguishable. Similarly, As³⁺ and Cd²⁺ or Cd²⁺ and Pb²⁺ can be separated because their sulfides form different precipitates under the same conditions.

Knowing which metal ions can or cannot be separated by H₂S is an important part of qualitative inorganic analysis. It helps in identifying unknown metals in laboratory experiments. The solubility of metal sulfides in acidic and basic conditions determines how effectively H₂S can be used to separate ions.

This concept is widely applied in analytical chemistry, environmental testing, and industrial processes to detect and differentiate metal ions in water, soil, and chemical samples.