Question

Which element is oxidized in this reaction? 2CuO+C→2Cu+CO2 Which element is reduced in this reaction? 16H++2Cr2O72−+C2H5OH→4Cr3++11H2O+2CO2

Answer 1

The element oxidized is the one whose oxidation number INCREASES......

Explanation:

And thus......

`stackrel(+II)" 2CuO" +Crarr2stackrel(0)Cu+CO_2uarr`

And here while copper (as `Cu^(2+)`) is reduced, carbon is oxidized, `stackrel(0)Crarrstackrel(+IV)C`.

The second reaction represents the reduction `Cr(VI+)` to `Cr(III+)`

`Cr_2O_7^(2-)+14H^+ +6e^(-) rarr 2Cr^(3+)+7H_2O` `(ii)`

And the oxidation of ethanol to carbon dioxide:

`H_3C-CH_2OH +H_2O rarr2CO_2+8H^(+) + 8e^(-)` `(iii)`

i.e. `H_3stackrel(-III)C-stackrel(-I)CH_2OHrarr2stackrel(+IV)CO_2`

We takes `4xx(ii)+3xx(iii)` to eliminate the electrons.....

`3H_3"CC"H_2OH +3H_2O +4Cr_2O_7^(2-)+56H^+ +24e^(-)rarr8Cr^(3+) + 28H_2O + 6CO_2+24H^(+) + 24e^(-)`

To give finally............

`3H_3"CC"H_2OH +4Cr_2O_7^(2-)+32H^+ rarr8Cr^(3+) + 25H_2O + 6CO_2`

`"Dichromate ion"` is reduced to `"chromic ion"`.........