Which metal sulphide is soluble in excess `NH_3` solution ?

Options

A. Zns
B. MnS
C. FeS
D. `Cr_2S_3`

Answer

To determine which metal sulfide is soluble in excess ammonia solution, we can follow these steps:

### Step 1: Understand the solubility of metal sulfides
Metal sulfides generally have low solubility in water. The solubility product constant (Ksp) indicates how soluble a compound is; a higher Ksp means greater solubility.

**Hint:** Remember that Ksp values are crucial in determining solubility.

### Step 2: Identify common metal sulfides
Common metal sulfides include:
- Zinc sulfide (ZnS)
- Manganese sulfide (MnS)
- Iron sulfide (FeS)
- Chromium(III) sulfide (Cr2S3)

**Hint:** List the sulfides you know and their general solubility behavior.

### Step 3: Compare Ksp values
- ZnS, MnS, and FeS have low Ksp values, indicating they are not very soluble in water or ammonia.
- Chromium(III) sulfide (Cr2S3) has a higher Ksp value, suggesting it is more soluble.

**Hint:** Look up the Ksp values if needed to compare the solubility of these sulfides.

### Step 4: Consider the effect of excess ammonia
When chromium(III) sulfide (Cr2S3) is added to excess ammonia, it forms a soluble complex:
\[ \text{Cr}_2\text{S}_3 + 6 \text{NH}_3 \rightarrow 2 \text{Cr(NH}_3\text{)}_6^{3+} + 3 \text{S}^{2-} \]

This reaction shows that Cr2S3 can dissolve in excess ammonia due to the formation of a coordination complex.

**Hint:** Complex formation can significantly increase solubility in certain cases.

### Step 5: Conclusion
Based on the above analysis, the metal sulfide that is soluble in excess ammonia solution is **Chromium(III) sulfide (Cr2S3)**.

**Final Answer:** Chromium(III) sulfide (Cr2S3) is the metal sulfide that is soluble in excess ammonia solution.