Question

1.2g of Mg (atomic mass=24 amu) will produce $MgO$ equal to:
A) 0.05 mol
B) 40g
C) 40mg
D) 4g

Answer 1

The answer includes the concept that involves the reaction of $Mg$ undergoing the aerial oxidation process that has a balanced chemical equation based on which amount of $MgO$ produced can be calculated.

Complete step by step solution:
From the basic concepts of chemistry we know that the reaction between Mg and oxygen yields $MgO$.
- This reaction is called particularly as aerial oxidation of magnesium alloys at elevated temperature to give the product as magnesium oxide.
- Aerial oxidation basically means oxidation of a compound or metal or its alloys in the presence of air.
-Magnesium when burnt in air undergoes an oxidation reaction that is, it accepts oxygen atoms where the oxidation number of magnesium changes from zero to +2.
- After burning in the presence of air it forms oxide which is the white coloured powder.
Now, according to the question given, we have atomic mass of Mg=24 amu.
The chemical reaction that is taking place during the aerial oxidation is represented below, $Mg+\dfrac{1}{2}{{O}_{2}}\to MgO$
This means that 1 mole of magnesium is required for producing 1 mole of $MgO$
Therefore, Number of moles of magnesium oxide ($MgO$) in 1.2 g is equal to $\dfrac{1.2}{24}$
$\Rightarrow 0.05mol$ of Magnesium.
Thus the total number of moles of magnesium present in 1.2g of Mg is $0.05mol$.

Hence, Option A) is the correct answer.

Note: Students may go wrong when multiple choice answers are given nearby to the actual answers which are as provided above as 40mg and 40g. Here, there is only a slight change in the units that is mg and g. Therefore, careful observation is needed while marking the answers.