Question

Question #f86bf

Answer 1

The carbide ion, `(C-=C)^-2`, has a formal charge of `-2`. The oxidation number of each `C` is `-I`.

Explanation:

The sum of the oxidation numbers must add to the charge of the ion. Since the `C`'s have a `-I` oxidation state, and the charge of acetylide is `-2`, this condition is satisfied. Of course, `Ca` is an alkaline earth metal, and has an oxidation number of `+II`.

To expand on the question, calcium carbide is clearly the derivative of acetylene gas, `H-C-=C-H`. Oxidation numbers may be assigned when we break the bonds, with the charge going to the most electronegative atoms (here `C`). Can you give the oxidation numbers of `C` for methane, ethane, and ethylene??