Which of the following cations form(s) black precipitate(s) with `H_(2)S (g)` ?

Options

A. `Cu^(2+)`
B. `Sb^(3+)`
C. `Pb^(2+)`
D. `Bi^(3+)`

Answer

To determine which cations form black precipitates with hydrogen sulfide (H₂S), we can analyze the reactions of various cations with H₂S. Here is a step-by-step solution:

### Step 1: Identify the cations
The cations we need to analyze for their reaction with H₂S are:
1. Cu²⁺ (Copper)
2. Sb³⁺ (Antimony)
3. Pb²⁺ (Lead)
4. Bi³⁺ (Bismuth)

### Step 2: Analyze the reaction of each cation with H₂S
- **Cu²⁺ (Copper)**:
- Reaction: Cu²⁺ + H₂S → CuS (s)
- Precipitate: Copper(II) sulfide (CuS) is formed, which is black in color.

- **Sb³⁺ (Antimony)**:
- Reaction: Sb³⁺ + H₂S → Sb₂S₃ (s)
- Precipitate: Antimony(III) sulfide (Sb₂S₃) is formed, which is orange in color.

- **Pb²⁺ (Lead)**:
- Reaction: Pb²⁺ + H₂S → PbS (s)
- Precipitate: Lead(II) sulfide (PbS) is formed, which is black in color.

- **Bi³⁺ (Bismuth)**:
- Reaction: Bi³⁺ + H₂S → Bi₂S₃ (s)
- Precipitate: Bismuth(III) sulfide (Bi₂S₃) is formed, which is black in color.

### Step 3: Summarize the results
From the analysis:
- Cu²⁺ forms a black precipitate (CuS).
- Sb³⁺ does not form a black precipitate (forms orange precipitate).
- Pb²⁺ forms a black precipitate (PbS).
- Bi³⁺ forms a black precipitate (Bi₂S₃).

### Conclusion
The cations that form black precipitates with H₂S are Cu²⁺, Pb²⁺, and Bi³⁺.

### Final Answer
The cations that form black precipitates with H₂S are:
- Cu²⁺ (Copper)
- Pb²⁺ (Lead)
- Bi³⁺ (Bismuth)