Question

What is the reducing agent in the reaction `2Na + 2H_2O -> 2NaOH + H_2`?

Answer 1

Sodium metal.

Explanation:

You're dealing with a redox reaction in which sodium metal, `"Na"`, is being oxidized to sodium cations, `"Na"^(+)`, and hydrogen is being reduced to hydrogen gas, `"H"_2`.

`2stackrel(color(blue)(0))("Na")_ ((s)) + 2stackrel(color(blue)(+1))("H")_ 2 stackrel(color(blue)(-2))("O")_ ((l)) -> 2stackrel(color(blue)(+1)) ("Na") stackrel(color(blue)(-2))("O") stackrel(color(blue)(+1))("H")_ ((aq)) + stackrel(color(blue)(0))("H") _(2(g))`

As you can see, the oxidation state of sodium goes from `color(blue)(0)` on the reactants' side, to `color(blue)(+1)` on the products' side, which implies that sodium metal is being oxidized.

On the other hand, the oxidation state of hydrogen goes from `color(blue)(+1)` on the reactants' side, to `color(blue)(0)` on the products' side, which implies that hydrogen is being reduced.

Now, a reducing agent is responsible with reducing a chemical species that takes part in a redox reaction. Similarly, an oxidizing agent is responsible with oxidizing a chemical species that takes part in a redox reaction.

You can thus say that the chemical species that is being oxidized acts as a reducing agent for the chemical species that is being reduced.

In this case, sodium metal is being oxidized, which implies that it is acting as the reducing agent.