Question

The mass of magnesium oxide formed by burning $1.216g$ magnesium in excess oxygen is:
A.$0.41g$
B. $1.52g$
C. $2.02g$
D. $2.82g$

Answer 1

Hint: Considering the chemical reaction between magnesium and oxygen, find out the amount of magnesium oxide produced by $1g$ of magnesium. And then, you can easily get the mass of magnesium oxide formed by $1.216g$ of magnesium.

Complete step by step answer:
When magnesium reacts with oxygen, it tends to give a white powdery substance that is magnesium oxide.
The following is a chemical reaction showing the combustion of magnesium (which is in solid form) in air (i.e. with oxygen) forming magnesium oxide,
$2M{{g}_{(s)}}+{{O}_{2(g)}}\to 2Mg{{O}_{(s)}}$

As per the above reaction,
Two molecules of magnesium form two molecules of magnesium oxide.
And we know, the mass of magnesium is $24g$ and that of oxygen is $16g$.
So, the mass of magnesium oxide i.e. MgO will be $24+16=40g$.
That means, $24g$ of magnesium will form $40g$ of magnesium oxide.
So, two molecules mean $2\times 24g$ i.e. $48g$ of magnesium will form $2\times 40g$ of magnesium oxide, which will be $80g$ of magnesium oxide.
If $48g$ of magnesium produces $80g$ of magnesium oxide then, $1g$ of magnesium will produce,
$48g\text{ Mg}\to 80g\text{ MgO}$

So, $1g\text{ Mg}\to \dfrac{80}{48}g\text{ MgO}$ i.e. $1.66g$ of MgO (Magnesium Oxide).
As we see that $1g$ of magnesium gives $1.66g$ of magnesium oxide then, $1.216g$ of magnesium will form:
$1g\text{ Mg}\to 1.66g\text{ MgO}$
So, $1.216g$ of magnesium will give,
$1.216g\text{ Mg}=1.216\times 1.66g\text{ MgO}=2.02g\text{ MgO}$
So, the correct answer is “Option C”.

Note: The possible mistake could be neglecting the number of molecules of magnesium producing magnesium oxide. Remember to balance the chemical reaction before calculating the mass of magnesium oxide produced by magnesium. Using the unitary method, finding these solutions is easy.