When dil.`HNO_(3)` is electrolysed

Options

A. `H_(2)(g)` is formed at anode
B. `O_(2)` gas is formed at anode
C. `NO_(2)` is formed at anode
D. `N_(2)` is formed at anode

Answer

To solve the question regarding the electrolysis of dilute HNO3, we will follow these steps:

### Step 1: Identify the Electrolyte
When dilute HNO3 is electrolyzed, it dissociates into ions:
\[ \text{HNO}_3 \rightarrow \text{H}^+ + \text{NO}_3^- \]

### Step 2: Determine the Ions Present
In addition to the ions from HNO3, water is also present, which dissociates into:
\[ \text{H}_2\text{O} \rightarrow \text{H}^+ + \text{OH}^- \]
Thus, the ions present during electrolysis are:
- \( \text{H}^+ \)
- \( \text{NO}_3^- \)
- \( \text{OH}^- \)

### Step 3: Identify the Electrodes
- The **cathode** is the negative terminal where reduction occurs.
- The **anode** is the positive terminal where oxidation occurs.

### Step 4: Reactions at the Cathode
At the cathode, positive ions are attracted. The only positive ion available is \( \text{H}^+ \). The reduction reaction that occurs is:
\[ \text{2H}^+ + 2e^- \rightarrow \text{H}_2 \]
This indicates that hydrogen gas (\( \text{H}_2 \)) is produced at the cathode.

### Step 5: Reactions at the Anode
At the anode, we have two possible ions: \( \text{NO}_3^- \) and \( \text{OH}^- \). We need to determine which ion will undergo oxidation. The standard electrode potentials are:
- \( \text{OH}^- \) has a reduction potential of approximately -0.40 V.
- \( \text{NO}_3^- \) has a reduction potential of approximately +0.96 V.

Since \( \text{OH}^- \) has a lower discharge potential, it will be oxidized:
\[ \text{4OH}^- \rightarrow \text{2H}_2\text{O} + \text{O}_2 + 4e^- \]
This indicates that oxygen gas (\( \text{O}_2 \)) is produced at the anode.

### Step 6: Summary of Products
From the electrolysis of dilute HNO3:
- **At the cathode**: Hydrogen gas (\( \text{H}_2 \)) is formed.
- **At the anode**: Oxygen gas (\( \text{O}_2 \)) is formed.

### Final Answer
When dilute HNO3 is electrolyzed, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode.

---