(I). 3CuO(s) + 2NH3(g) ----- 3Cu(s) + 3H2O(l) + N2(g) (II). 2NH3(g) + 3Cl2(g) ----- 6HCl(g) + N2(g) (III)…

Analysis of the Question

To determine what these reactions demonstrate, we need to examine the role of ammonia ($NH_3$) in each chemical equation. Specifically, we need to look at whether ammonia is gaining or losing electrons (or oxygen/hydrogen) in these processes.

Concept Explanation

• Reducing Agent: A substance that causes reduction in another substance by donating electrons, adding hydrogen, or removing oxygen. In the process, the reducing agent itself gets oxidized (its oxidation state increases).
• Oxidizing Agent: A substance that causes oxidation in another substance by accepting electrons, removing hydrogen, or adding oxygen. In the process, the oxidizing agent itself gets reduced.

Let's look at the oxidation state of Nitrogen in $NH_3$: In $NH_3$, the oxidation state of Nitrogen is -3. In the products ($N_2$), the oxidation state of Nitrogen is 0. Since the oxidation state increases from -3 to 0, Nitrogen is being oxidized. Therefore, ammonia acts as a reducing agent.

Step-by-Step Solution

Let's analyze the reactions:

1. Reaction (I): $3CuO + 2NH_3 \rightarrow 3Cu + 3H_2O + N_2$ • Copper (II) oxide ($CuO$) loses oxygen to become Copper ($Cu$). This is reduction. • Ammonia ($NH_3$) removes the oxygen from $CuO$. Therefore, ammonia is the reducing agent.

2. Reaction (II): $2NH_3 + 3Cl_2 \rightarrow 6HCl + N_2$ • Chlorine ($Cl_2$) gains hydrogen (or loses electrons) to become $HCl$. • Ammonia provides the hydrogen and is oxidized to $N_2$. Ammonia is the reducing agent.

3. Reaction (III): $4NH_3 + 3O_2 \rightarrow 6H_2O + 2N_2$ • Oxygen ($O_2$) is reduced to water. • Ammonia is oxidized to nitrogen gas. Ammonia is the reducing agent.

In all three equations, ammonia is removing oxygen from a metal oxide, reacting with a non-metal (chlorine), or reacting with oxygen. In every case, ammonia is being oxidized, which confirms its role as a reducing agent.

Conclusion

Since ammonia is causing the other substances to be reduced while it is being oxidized, these reactions demonstrate the reducing properties of ammonia.

Exam Tip

Whenever you see ammonia reacting with metal oxides or halogens in JAMB chemistry, always look for the formation of Nitrogen gas ($N_2$). The conversion of $NH_3$ to $N_2$ is a classic indicator that ammonia is acting as a reducing agent!