Question

Calculate the number of moles in $369$ grams of $CaOC{l_2}$
A.$1$
B.$2$
C.$3$
D.$4$

Answer 1

The molar mass of a compound is equal to the sum of the atomic masses of its constituent atoms in g/mol.
-Although there is no physical way of measuring the number of moles of a compound, we can relate its mass to the number of moles by using the compound’s molar mass as a direct conversion factor.
-To convert between mass and number of moles, you can use the molar mass of the substance.

Complete answer:
We know,
The molar mass of any element can be determined by finding the atomic mass of the element on the periodic table. For $CaOC{l_2}$, we add atomic weights of one unit of calcium, one unit of oxygen and two units of chlorine from the atomic table to find the total molecular weight of the salt.
Going by this way, we can say that
Molecular weight of $CaOC{l_2} = 127$
The formula for number of moles is given by
$n = \dfrac{m}{M}$
where,
$n =$ no. of moles
$m =$ mass of a substance
$M =$ molar mass (which is equivalent to atomic weight on the periodic table)
Given,
Mass of $CaOC{l_2}$ is $369$ grams
Substituting the values in the formula stated above, we get
$n = \dfrac{{369}}{{127}}$
$\Rightarrow n = 3$
So we can say that there are $3$ moles of $CaOC{l_2}$ present in $369$ grams by weight of the salt.
So the correct answer is option C.

Note:
-One can use Avogadro’s number to convert the number of moles to the number of atoms.
-One mole is equal to $6.022 \times {10^{23}}$ molecular entities (Avogadro’s number), and each element has a different molar mass depending on the weight of its atoms $6.022 \times {10^{23}}$ (1 mole).
-By recognizing the relationship between the molar mass (grams per mole) moles (mol), and particles, scientists can use dimensional analysis to convert between mass, number of moles and number of atoms very easily.