Question

When manganese dioxide is heated with aluminium powder, the products obtained are:
A. Mn, $A{{l}_{2}}{{O}_{3}}$and heat
B. MnO and $A{{l}_{2}}{{O}_{3}}$
C. MnO $A{{l}_{2}}{{O}_{3}}$ and heat
D. Mn and $A{{l}_{2}}{{O}_{3}}$

Answer 1

Hint: Aluminium is more reactive than Manganese. And also Aluminium will act as a reducing agent. A reducing agent removes oxygen from other compounds and gets oxidized in a chemical reaction. Or we can say that, this reaction will be a single displacement reaction.

Step by step answer:
We can write the chemical reaction as follows:
$3Mn{{O}_{2}}\text{ }+\text{ }4Al\text{ }\to \text{ }3Mn\text{ }+\text{ }2A{{l}_{2}}{{O}_{3}}+heat$
As we can see in the above reaction that it is a single displacement reaction. It is the more reactive aluminium that displaces manganese from manganese dioxide.
In other words we can say that, when we heat manganese dioxide with aluminium powder, aluminium powder will act as a strong reducing agent. It will take up oxygen and it gets oxidised and forms Aluminium oxide and heat.
We can also describe it as the oxidation number of Mn in $Mn{{O}_{2}}$ is +4 whereas the oxidation number of Mn is zero on the product side of chemical reaction. Hence the change in oxidation number occurs from +4 to 0. Overall oxidation number decreases hence it is reduced and is called an oxidizing agent.
On the contrary, the oxidation number of Al is zero on the reactant side of chemical reaction and it changes to +3 in$A{{l}_{2}}{{O}_{3}}$. Hence the oxidation number increases so it is an oxidation reaction and Al is a reducing agent.

Note: We can understand this question with many concepts. They are as follows:
First is in order of chemical reactivity. We know from the reactivity series that aluminium is more reactive than manganese. So when heat manganese dioxide and aluminium. Aluminium displaces manganese from manganese dioxide and itself formed into aluminium oxide.
Next we understand it by redox reaction: Aluminium is a strong reducing agent. We should note that aluminium leads manganese in the ease of oxidation or aluminium is more strongly reducing than manganese hence aluminium is more reactive than manganese. Also we can give the reason that aluminium has lower first ionization energy than manganese. Lower the ionization energy, more reactive the element is.