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: Name the compound.
$Mg(NH_4)PO_4 \cdot 6H_2O$ is magnesium ammonium phosphate, also called struvite. It shows up when we test for magnesium ions.

Step 2: How it forms.
A magnesium solution treated with ammonium chloride, ammonia and disodium hydrogen phosphate throws down this salt:
\[ Mg^{2+} + NH_4^+ + HPO_4^{2-} + 6H_2O \rightarrow Mg(NH_4)PO_4 \cdot 6H_2O + H^+ \]

Step 3: Look at the precipitate.
Magnesium has no partly filled d orbitals, so its salts are not coloured. The crystals come out clean and white.

Step 4: State the colour.
So the colour of this compound is white.
\[ \boxed{\text{White}} \]