Question

What happens when steam is passed over red hot iron?
A. No reaction takes place.
B. ${{\text{O}}_2}{\text{ and Fe}}{\left( {{\text{OH}}} \right)_2}$ are formed.
C. ${H_2}{\text{ and F}}{{\text{e}}_3}{O_4}$ are formed.
D. ${H_2}{\text{ and F}}{{\text{e}}_2}{O_3}$ are formed.

Answer 1

Hint- Iron being less reactive does not react with water under ordinary conditions. Reaction takes place only when the iron is red hot and water is in the form of steam. The reaction takes place as a reduction reaction in which Magnetite is formed and hydrogen gas is liberated.

Complete answer:
The reaction of metals with water depends on the reactivity of the metal.
1. Alkali metals are reactive so that they react vigorously and exothermically with water. In some cases the heat generated is sufficient to ignite the metal.
2. In general the reactions of metals with water produce hydrogen gas and the hydroxides of the metals.
3. Metals with moderate to low reactivity react very slowly with water. However, they react moderately with steam when heated and give hydrogen gas and metal oxides.
4. Metals low in the metal reactivity series do not react with water even at high temperatures.

Iron (Fe) being moderate reactive does not react with ordinary water. Reaction takes place only when the iron is red hot and water is in steam form.
The reaction is as follow:
$3{\text{Fe + 4}}{{\text{H}}_2}{\text{O}} \to {\text{ F}}{{\text{e}}_3}{{\text{O}}_4} + 4{{\text{H}}_2} \uparrow$
Here ‘Fe’ is red hot and steam is passed over it.
The product formed are Magnetite (${\text{F}}{{\text{e}}_3}{{\text{O}}_4}$) and Hydrogen gas is liberated.

Here water is reduced to Hydrogen gas. Therefore, it is a reduction reaction.

So, option C is correct.

Note- In the question involving reaction with water, you should have knowledge about the reactivity series of metal. The reactivity series of metals in descending order is given below :
Potassium>Sodium>Lithium>Calcium>Magnesium>Zinc>Iron>hydrogen>Copper>Gold
Potassium and Calcium are the most reactive metals. They react vigorously with water and give a lot of heat. So, they are kept in kerosene. Gold does not react with water or air at all. So, it is used as an ornamental element.