Question

If the relative molecular mass of ammonium nitrate is 80, calculate the percentage of nitrogen and oxygen in ammonium nitrate. (N = 14, H = 1, O = 16).
A.40%, 50%
B.40%, 60%
C.35%, 60%
D.35%, 40%

Answer 1

To answer this question we should first find the molecular mass of individual atoms present in the compound and then we should calculate the percentage of individual atoms in the compound by dividing molecular mass to total and multiply to 100 at the end.

Step by step answer:

We should first know about relative molecular mass i.e.., the relative molecular mass/relative formula mass is defined as the sum of all the individual atomic masses of all the atoms in the formula (Mr). If the individual atomic masses of all the atoms in a formula are added together then we had calculated the relative formula mass.
Mr = Relative formula mass
      = relative molecular mass
      = the sum of all the atomic masses for ALL the atoms in a given formula.
Now, as given in the question the relative molecular mass of ammonium is 80. And then we calculate the mass of nitrogen and oxygen in ammonium nitrate.
Mass of nitrogen in 1 mole of ammonium nitrate ($N{{H}_{4}}N{{O}_{3}}$) = $2\times 14=28g$
Mass of oxygen in 1 mole of ammonium nitrate ($N{{H}_{4}}N{{O}_{3}}$) = $16\times 3=48g$
Mass of one mole of $N{{H}_{4}}N{{O}_{3}}$= 80 gram
Now, we will find the percentage of nitrogen in ammonia nitrate.
$=\dfrac{mass\,of\,nitrogen}{mass\,of\,ammonia\,nitrate}\times 100=\dfrac{28}{80}\times 100=35%$
Now, we will find the percentage of oxygen in ammonia nitrate.
$=\dfrac{mass\,of\,oxygen}{mass\,of\,ammonia\,nitrate}\times 100=\dfrac{48}{80}\times 100=60%$
So, now we know our correct answer. The percentage of nitrogen and oxygen in ammonium nitrate is 35% and 60%.
The correct option is C.
Note:
We should know that mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture. Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%. We should know that mass percent is the mass of the element or solute divided by the mass of the compound or solute. The result is multiplied by 100 to give a percent.