Question

please explain the second reaction.

Answer 1

Cr2O72− is charged, hence the sum of the oxidation numbers of the 2 chromium atoms and the the 7 oxygen atoms is −2.

n most cases, the oxidation number of oxygen is taken as −2. However in the cases of peroxides and superoxides, the oxidation number of oxygen is−1 and −12respectively. There is another case, where the oxidation number of oxygen is different but I wont discuss that here. In this case we are taking oxygen to have −2oxidation state.

Let us take the oxidation number of Cr to be x, since there are 2 Cr atoms, the oxidation number for both of them as a whole is 2x

Combining the above rules, we get

2x+(7∗(−2))=−2

2x−14=−2

2x=12

x=+6

Where xis the oxidation state of chromium atom.

Answer 2

Cr2O72− is charged, hence the sum of the oxidation numbers of the 2 chromium atoms and the the 7 oxygen atoms is −2.

n most cases, the oxidation number of oxygen is taken as −2. However in the cases of peroxides and superoxides, the oxidation number of oxygen is−1 and −12respectively. There is another case, where the oxidation number of oxygen is different but I wont discuss that here. In this case we are taking oxygen to have −2oxidation state.

Let us take the oxidation number of Cr to be x, since there are 2 Cr atoms, the oxidation number for both of them as a whole is 2x

Combining the above rules, we get

2x+(7∗(−2))=−2

2x−14=−2

2x=12

x=+6

Where xis the oxidation state of chromium atom.