Question

What is the percentage by weight of calcium in calcium carbonate $(CaC{O_3})$ ?
A. 10%
B. 40%
C. 20%
D. 30%

Answer 1

Hint – 1 Ca atom molar mass is 40, 1 C atom molar mass is 12, and 1 Oxygen atom molar mass is 16, so find the total weight of Calcium Carbonate and then find the percentage.

Complete answer:
Formula used - $\% Ca = \dfrac{{WeightofCa.in(CaC{O_3})}}{{TotalweightofCaC{O_3}}} \times 100\%$
We have been given to find the percentage by weight of calcium in calcium carbonate $(CaC{O_3})$
So, first we will write the weight of each atom.
So, the molar mass of 1 calcium atom is 40.
Molar mass of 1 carbon atom is 12.
And, the molar mass of 1 oxygen atom is 16.
So, by adding the molar masses of each atom we can find the total weight.
Also, since there are three oxygen atoms in $(CaC{O_3})$ so, molar mass of 3 oxygen atoms will be $16 \times 3 = 48$
So, no finding the total weight, we get-
$W = 40 + 12 + 48 = 100$
Now, the percentage by weight of calcium in calcium carbonate $(CaC{O_3})$ is-
$\% Ca = \dfrac{{WeightofCa.in(CaC{O_3})}}{{TotalweightofCaC{O_3}}} \times 100\%$
Therefore, it will be-
$\% Ca = \dfrac{{40}}{{100}} \times 100 = 40\%$
Therefore, the percentage by weight of calcium in calcium carbonate is 40%.

Hence, the correct option is B.

Note – Whenever such types of questions appear then first find the total weight of the compound given, as mentioned in solution the total weight of the calcium carbonate $(CaC{O_3})$ is $W = 40 + 12 + 48 = 100$ , then as we can see that there is one atom of Ca in $(CaC{O_3})$ , so the percentage of weight of calcium in calcium carbonate will be $\% Ca = \dfrac{{WeightofCa.in(CaC{O_3})}}{{TotalweightofCaC{O_3}}} \times 100\%$.