Question

What is redox reaction ? When a magnesium ribbon burns with a dazzling flame and forms a white ash , is magnesium ribbon is oxidised or reduced

Answer 1

Well, redox reactions involve formal changes in oxidation state with respect to reactant and product...

Explanation:

All combustion reactions are redox reactions...

And here we put in oxidation numbers...

`stackrel(0)Mg(s) + 1/2stackrel(0)O_2rarrunderbrace(stackrel(0)Mgstackrel(-II)O(s))_"the white ash"`

And so here magnesium has been oxidized, i.e. lost electons, to give `Mg^(2+)`, and dioxygen has been reduced to the oxide dianion.

Formally we could use the method of half-equations...`"oxidation"`

`underbrace(Mg(s) rarr Mg^(2+) + 2e^(-))_"formal oxidation"` `(i)`

...accompanied by `"reduction"`

`underbrace(1/2O_2(g) + 2e^(-) rarr O^(2-))_"formal reduction"` `(ii)`

Add `(i)` and `(ii)` to give...

`Mg(s) + 1/2O_2(g) rarr MgO(s)`...as before....