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 oxygen, we can follow these steps:

### Step 1: Write the combustion reaction of ethane
When ethane is burnt in excess oxygen, the reaction can be represented as:
\[ \text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \]

### Step 2: Balance the combustion reaction
To balance the reaction, we need to ensure that the number of atoms of each element is the same on both sides. The balanced equation is:
\[ 2 \text{C}_2\text{H}_6 + 7 \text{O}_2 \rightarrow 4 \text{CO}_2 + 6 \text{H}_2\text{O} \]

### Step 3: Determine the oxidation state of carbon in ethane
In ethane (C2H6), the oxidation state of carbon can be calculated as follows:
- Each hydrogen (H) has an oxidation state of +1.
- Let the oxidation state of carbon be \( x \).
- The equation for the oxidation state in C2H6 is:
\[ 2x + 6(+1) = 0 \]
This simplifies to:
\[ 2x + 6 = 0 \]
\[ 2x = -6 \]
\[ x = -3 \]
So, the oxidation state of carbon in ethane is -3.

### Step 4: Determine the oxidation state of carbon in carbon dioxide
In carbon dioxide (CO2), the oxidation state of carbon can be calculated as follows:
- Each oxygen (O) has an oxidation state of -2.
- Let the oxidation state of carbon be \( y \).
- The equation for the oxidation state in CO2 is:
\[ y + 2(-2) = 0 \]
This simplifies to:
\[ y - 4 = 0 \]
\[ y = +4 \]
So, the oxidation state of carbon in carbon dioxide is +4.

### Step 5: Calculate the change in oxidation number
Now, we can find the change in oxidation number of carbon from ethane to carbon dioxide:
- Initial oxidation state in ethane = -3
- Final oxidation state in carbon dioxide = +4
- Change in oxidation number = Final oxidation state - Initial oxidation state
\[ \text{Change} = +4 - (-3) = +4 + 3 = +7 \]

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

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