When ethane is burnt in excess of oxygen,, the oxidation number of carbon changes by

Options

A. `+8`
B. `+7`
C. `+3`
D. `+4`

Answer

To determine the change in the oxidation number of carbon when ethane (C2H6) is burnt in excess of oxygen, we can follow these steps:

### Step 1: Write the balanced chemical equation for the combustion of ethane.
The combustion of ethane in excess oxygen can be represented as:
\[ 2 \text{C}_2\text{H}_6 + 7 \text{O}_2 \rightarrow 4 \text{CO}_2 + 6 \text{H}_2\text{O} \]

### Step 2: Determine the oxidation state of carbon in ethane (C2H6).
In ethane (C2H6), we can calculate the oxidation state of carbon (C) using the following formula:
- Let the oxidation state of carbon be \( x \).
- The oxidation state of hydrogen (H) is +1.

The equation for the oxidation state in ethane is:
\[ 2x + 6(+1) = 0 \]
Solving for \( x \):
\[ 2x + 6 = 0 \\ 2x = -6 \\ x = -3 \]
Thus, the oxidation state of carbon in ethane is -3.

### Step 3: Determine the oxidation state of carbon in carbon dioxide (CO2).
In carbon dioxide (CO2), we can calculate the oxidation state of carbon:
- Let the oxidation state of carbon be \( y \).
- The oxidation state of oxygen (O) is -2.

The equation for the oxidation state in carbon dioxide is:
\[ y + 2(-2) = 0 \]
Solving for \( y \):
\[ y - 4 = 0 \\ y = +4 \]
Thus, the oxidation state of carbon in carbon dioxide is +4.

### Step 4: Calculate the change in oxidation state.
Now we can find the change in the oxidation state of carbon from ethane to carbon dioxide:
\[ \text{Change} = \text{Final oxidation state} - \text{Initial oxidation state} \\ \text{Change} = +4 - (-3) \\ \text{Change} = +4 + 3 \\ \text{Change} = +7 \]

### Conclusion:
The oxidation number of carbon changes by +7 when ethane is burnt in excess of oxygen.

### Final Answer:
The oxidation number of carbon changes by **+7**.

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