What is the average oxidation number of carbon in dichloroacetic acid (CHCl2COOH)?
The Correct Answer and Explanation is:
Correct Answer: +2
Explanation:
To find the average oxidation number of carbon in dichloroacetic acid (CHCl₂COOH), begin by examining the structure and assigning known oxidation numbers to other atoms.
Chemical formula: CHCl₂COOH
This compound contains two carbon atoms.
Break it down into groups:
- One carbon is part of the CHCl₂ group.
- One carbon is part of the COOH (carboxylic acid) group.
Known oxidation numbers:
- Hydrogen (H) = +1
- Oxygen (O) = –2
- Chlorine (Cl) = –1
Now apply the rules to calculate the total oxidation state for each carbon:
Step 1: Assign oxidation numbers to atoms in CHCl₂COOH
Let:
- Carbon in CHCl₂ be C₁
- Carbon in COOH be C₂
COOH group:
Structure: –C(=O)OH
Atoms involved: 1 carbon, 2 oxygen atoms, 1 hydrogen
- Hydrogen = +1
- Two oxygen atoms = 2 × (–2) = –4
Total contribution from H and O = +1 + (–4) = –3
To balance the group to neutral, carbon (C₂) must be +3
CHCl₂ group:
Atoms: 1 hydrogen, 2 chlorine atoms, 1 carbon
- Hydrogen = +1
- Chlorines = 2 × (–1) = –2
Total contribution from H and Cl = +1 + (–2) = –1
To balance the group, carbon (C₁) must be +1
Step 2: Find average oxidation number of both carbon atoms
Total oxidation number of carbon atoms = +1 (C₁) + +3 (C₂) = +4
Number of carbon atoms = 2
Average oxidation number = +4 ÷ 2 = +2
Conclusion:
The average oxidation number of carbon in dichloroacetic acid is +2. This value represents the mean oxidation state of all carbon atoms present in the molecule.