Question

The colour of \( \text{Mg(NH}_4\text{)PO}_4\cdot\text{6H}_2\text{O} \) is:

• A. White
• B. Green
• C. Black
• D. Yellow

Hint:

The formation of a white crystalline precipitate of \( \text{Mg(NH}_4\text{)PO}_4\cdot\text{6H}_2\text{O} \) is a classic confirmatory test for magnesium ions ($Mg^{2+}$) in group analysis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Magnesium ammonium phosphate hexahydrate, \( \text{Mg(NH}_4\text{)PO}_4\cdot\text{6H}_2\text{O} \) (commonly known as struvite), is formed during the qualitative estimation and identification of magnesium or phosphate ions.

Step 2: Key Formula or Approach:
When a magnesium salt solution is treated with ammonium chloride, ammonium hydroxide, and disodium hydrogen phosphate, a characteristic crystalline precipitate is formed.
The physical appearance and color of this precipitate serve as a confirmatory test.

Step 3: Detailed Explanation:
The reaction for the formation of the precipitate can be written as:
\[ \text{Mg}^{2+} + \text{NH}_4^+ + \text{HPO}_4^{2-} + 6\text{H}_2\text{O} \rightarrow \text{Mg(NH}_4\text{)PO}_4\cdot\text{6H}_2\text{O}\downarrow + \text{H}^+ \]
This precipitate forms as distinct, white, distinctively shaped (often described as star-shaped or coffin-lid-shaped) crystals.
Thus, the color of the compound is white.

Step 4: Final Answer:
The color of \( \text{Mg(NH}_4\text{)PO}_4\cdot\text{6H}_2\text{O} \) is White.