Question

Calculate the ratio of atomic masses of carbon and oxygen in \[C{O_2}\] molecules.
\[
  {A.{\text{ }}3:7} \\
  {B.{\text{ }}3:4} \\
  {C.{\text{ }}3:8} \\
  {D.{\text{ }}4:5}
\]

Answer 1

Hint: First we have to calculate the mass of each oxygen and carbon in one mole of \[C{O_2}\] and then we can find the ratio between them in \[C{O_2}\] molecule.

Complete answer:
Let’s start by discussing the atomic mass. Atomic mass is the weighted average of all the isotopes of that particular element. The average is taken in such a way that their abundance is also taken into consideration. In the case of molecules, the atomic mass is calculated by adding the atomic masses of each atom present in the molecule for example the atomic mass of \[N{H_3}\] will be \[14 + 1 + 1 + 1\] which is equal to 17 (atomic mass of nitrogen is 14, hydrogen is 1).
Now coming back to the question we are given the molecule \[C{O_2}\] which comprises 2 oxygen atoms and one carbon atom. The atomic mass of oxygen is 16 and that of carbon is 12. Since we are having two oxygen atoms this means that the total mass of oxygen in \[C{O_2}\] is two times the mass of oxygen which means \[2{\text{ }} \times {\text{ }}16\] which is equal to 32.
Now, for finding the ratio of atomic masses of carbon and oxygen we will divide them to a level where they reach their lowest value as the numerator and denominator, and if we proceed with the further division a decimal will be obtained which is not acceptable.
\[C:O{\text{ }} = {\text{ }}12:32\]
\[6:16\]
\[3:8\]
So, we can conclude that the ratio of atomic masses is \[3:8\] which is the option number C.

Note:
We must know that the atomic mass has a lot of significance as all the things are made up of atoms and their mass is the sum of the mass of these atoms. The molecules also have some mass and for calculating their mass we require the masses of each individual atom and here comes the role of atomic mass as well as the ratio of atomic masses in that molecule.