Question

Calculate the molecular mass of the limestone.
A. ${\text{ }}CaC{O_2} = 84gmo{l^{ - 1}}$
B. $CaC{O_3} = 100gmo{l^{ - 1}}$
C. $C{a_2}C{O_3} = 140gmo{l^{ - 1}}$
D. $CaCO = 68gmo{l^{ - 1}}$

Answer 1

Lime is a white amorphous inorganic compound. It is a salt of calcium. Molecular mass means the weight of the 1-mole amount of a compound. And according to the mole concept, we know 1 mole of any substance is equal to its molecular weight. And 1 mole is also equal to Avogadro’s number of atoms i.e. ${\text{6}}{\text{.023}} \times {\text{1}}{{\text{0}}^{23}}$.

Complete step by step answer:
Lime is an inorganic compound made of calcium, carbon, and oxygen. It can be formed by the reaction of calcium hydroxide with carbon dioxide as follows,
$Ca{(OH)_2} + C{O_2} \to CaC{O_3} + {H_2}O$
This reaction is commonly known as carbonatation.
The chemical name of lime is calcium carbonate with the formula, $CaC{O_3}$.
Now the molecular weight of calcium carbonate can be found by summation of the atomic weight of each element.
Now, the atomic weight of calcium is $40gmo{l^{ - 1}}$. The atomic weight of carbon is $12gmo{l^{ - 1}}$. The atomic weight of oxygen is $16gmo{l^{ - 1}}$.
Now, the molecular weight of the calcium carbonate (lime) is

$$= 40 + 12 + (16 \times 3)\, \\\ = 52 + 48 \\\ = 100gmo{l^{ - 1}} \\\$$

Therefore, the correct answer is, B.

Additional information:
Calcium hydroxide is commonly known as slaked lime. It is an inorganic compound having formula ${\text{Ca(}}OH{)_2}$ and is colorless in its hexagonal crystalline form. There exists an ionic bond between the calcium and two hydroxide ions. Direct exposure to concentrated ${\text{Ca(}}OH{)_2}$ can affect the lungs and might even lead to blindness.
It is chemically very reactive. When it is dissolved in water until a saturation point, it produces a solution called lime water as follows.
$CaO + {H_2}O \to Ca{(OH)_2}$ ,
which acts as a moderate base. Limewater reacts with many acids and forms salts. The saturated solution of calcium hydroxide in water can also react with metal and dissolves them. For example, aluminum.

Note:
Calcium hydroxide releases hydroxide ions when dissolved in aqueous solutions. The liberation of $O{H^ - }$ ions due to electrocyclic dissociation confirms that it is a base. In the case of calcium hydroxide, it has two hydroxide ions that dissociate when dissolved in an aqueous medium. This makes it acidic in nature and results in the acidity of the compound.