Question

What is correct for 10g of $CaC{O_3}$?
A. it contains 1 g-atom of carbon.
B. it contains 0.3 g-atom of oxygen.
C. it contains 12 g of calcium.
D. none of these

Answer 1

$CaC{O_3}$ is known as Calcium carbonate. Calcium carbonate decomposes to form Calcium oxide and emits Carbon dioxide. Calcium oxide has calcium and oxygen; Carbon dioxide has carbon and oxygen. Find the molecular weight of calcium carbonate, the corresponding weight of calcium, oxygen, and carbon of calcium carbonate.

Complete step by step answer:
The molecular formula of Calcium Carbonate is $CaC{O_3}$. Calcium Carbonate contains calcium, carbon, and oxygen. Calcium Carbonate on heating decomposes into Calcium Oxide ($CaO$) and emits Carbon dioxide ($C{O_2}$).
$CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2}$
This reaction is a decomposition reaction.
The atomic weight of Calcium is 40g, the atomic weight of Carbon is 12g and the atomic weight of Oxygen is 16g.
Therefore, the molecular weight of Calcium Carbonate is $1 \times 40 + 1 \times 12 + 3 \times 16 = 40 + 12 + 48 = 100g$
100 grams of Calcium Carbonate contains 40 grams of Calcium, 12 grams of Carbon and 48 grams of oxygen.
In the same way, 10 grams of Calcium Carbonate contains 4 grams of Calcium, 1.2 grams of Carbon, and 4.8 grams of Oxygen.
No .of gram atoms in 1.2 grams of Carbon is $\dfrac{{1.2}}{{12}} = 0.1$
No .of gram atoms in 4.8 grams of Oxygen is $\dfrac{{4.8}}{{16}} = 0.3$
Therefore, 10 grams of Calcium Carbonate contains 0.3 g-atom of Oxygen, 0.1 g-atom of Carbon, and 4 grams of calcium.

The correct option is Option B

Note:
Do not confuse gram atom with no. of moles. 1 gram atom is the no. of atoms present in 1 gram of the substance whereas 1 mole of a substance has $6.023 \times {10^{23}}$ particles and the particles can be atoms, ions or molecules.