Question

Urea reacts with water to form $A$ which will decompose to form $B$. $B$ when passed through $Cu^{2+}(aq)$, deep blue colour solution C is formed. What is the formula of C from the following

• A. $CuSO_4$
• B. $[Cu(NH_3)_4]^{2+}$
• C. $Cu(OH)_2$
• D. $CuCO_3.Cu(OH)_2$

Answer 1

The Correct Option is B

To solve this problem, we first need to understand the series of chemical reactions described:

1. Reaction of Urea with Water:
   • Urea, with the chemical formula \((\text{NH}_2)_2\text{CO}\), reacts with water to form \(A\), which is ammonium carbamate, \(\text{NH}_4\text{OCONH}_2\).
   • Urea hydrolysis: \((\text{NH}_2)_2\text{CO} + \text{H}_2\text{O} \rightarrow \text{NH}_4\text{OCONH}_2\)
2. Decomposition of Ammonium Carbamate:
   • The ammonium carbamate decomposes to form ammonia \((B, \text{NH}_3)\) and carbon dioxide: \(\text{NH}_4\text{OCONH}_2 \rightarrow 2\text{NH}_3 + \text{CO}_2\)
3. Reaction of Ammonia with Copper (II) Ions:
   • Ammonia, when reacted with copper (II) ions \((Cu^{2+})\), forms a deep blue complex. \(\text{Cu}^{2+} + 4\text{NH}_3 \rightarrow [\text{Cu}(\text{NH}_3)_4]^{2+}\)
   • This complex ion is known as tetraamminecopper(II), which gives a characteristic deep blue color in solution.

Now, let's analyze the given options to identify the compound \(C\):

• \(\text{CuSO}_4\): Copper(II) sulfate is a blue crystalline solid but does not match the deep blue solution described.
• \([\text{Cu}(\text{NH}_3)_4]^{2+}\): This is the correct formula for the deep blue complex ion formed in the reaction of ammonia with \(\text{Cu}^{2+}\).
• \(\text{Cu(OH)}_2\): Copper(II) hydroxide is a blue precipitate, not a solution.
• \(\text{CuCO}_3.\text{Cu(OH)}_2\): This is a basic copper carbonate, which does not match our described product.

Thus, the correct answer is the formation of the complex \([\text{Cu}(\text{NH}_3)_4]^{2+}\).