Question

The formula, $CaC{O_3}$, quantitatively signifies that:
This question has multiple correct options.
A) One molecule of calcium carbonate
B) One molecule of calcium carbonate is made up of calcium, one atom of carbon and three atoms of oxygen.
C) 100 parts by weight of calcium carbonate [At. Wt. Ca = 40, C = 12, O = 16]
D) 40 parts by weight of calcium, 12 parts by weight of carbon and 48 parts by weight of oxygen.

Answer 1

To answer this question, you should know the molecular composition of $CaC{O_3}$ or calcium carbonate. It is composed of three elements as can be seen in its molecular formula. Calculate the molecular weight of $CaC{O_3}$ and for this you should know atomic masses of the three elements present in the molecule.

Complete step by step answer:
We are given a molecular formula, $CaC{O_3}$ and let us examine it in points:
- $CaC{O_3}$ is known with a chemical name called calcium carbonate. As it can be seen in its molecular formula that, one molecule of $CaC{O_3}$ is composed of one atom of calcium (Ca), one atom of carbon (C), and three atoms of oxygen (O).

- Atomic weight of Calcium = 40 g
Atomic weight of carbon = 12 g
Atomic weight of oxygen = 16 g
Therefore, $CaC{O_3}$molecule has 40 parts by weight of calcium, 12 parts by weight of carbon and 48 parts by weight of oxygen (since, 16 g $\times$ 3 oxygen atoms = 48 g).

- Now, calculating the molecular weight of $CaC{O_3}$.
Since, molecular weight is the sum of atomic weights of the elements present in the molecule.
Therefore, molecular weight of $CaC{O_3}$= 1(At. wt of Ca) + 1(At. wt. of C) + 3(At. wt. of O)
Molecular weight of $CaC{O_3}$= 1(40) + 1(12) + 3(16) = 100 g
Hence, calcium carbonate is 100 parts by weight.
Thus, on concluding above all points, it is clear that all the given options are correct.
So, the correct answer is “Option A,B, C and D”.

Note: If we talk about mass percent of each element in the compound, $CaC{O_3}$, then it will be:
Mass % of an element = $\dfrac{{{\text{mass of that element}}}}{{{\text{molecular mass of the compound}}}} \times 100$
Mass % of calcium = $\dfrac{{40}}{{100}} \times 100 = 40\%$
Mass % of carbon = $\dfrac{{12}}{{100}} \times 100 = 12\%$
Mass % of oxygen = $\dfrac{{3 \times 16}}{{100}} \times 100 = 48\%$