Question

A mole is defined as:
A) Molecular weight expressed in grams.
B) Molecular weight divided by $1{\text{ g}}$ of ${{\text{H}}_{\text{2}}}$.
C) Number of particles contained in $12{\text{ g}}$ of ${\text{C}}$ of atomic mass 12.
D) Number of molecules contained in one litre of a gas at STP.

Answer 1

To solve this we must know that mole is the unit of measurement used for measuring the amount of a substance in the International System of Units (SI). The unit of mole is mol. Mole is a standard scientific unit which is used for measuring large quantities of small entities like ions or atoms or molecules.

Complete solution:
We know that mole is the unit of measurement used for measuring the amount of a substance in the International System of Units (SI). The unit of mole is mol. mole is a standard scientific unit which is used for measuring large quantities of small entities like ions or atoms or molecules.
Mole is the ratio of mass of a substance in grams to the molar mass of the substance n grams per mol. Thus,
${\text{Number of moles}}\left( {{\text{mol}}} \right) = \dfrac{{{\text{Mass}}\left( {\text{g}} \right)}}{{{\text{Molar mass}}\left( {{\text{g/mol}}} \right)}}$
Thus, mole is not molecular weight expressed in grams. Thus, option (A) and option (B) are not correct.
$12{\text{ g}}$ of ${\text{C}}$ of atomic mass 12 contains one mole of carbon. $12{\text{ g}}$ of ${\text{C}}$ of atomic mass 12 contains $6.022 \times {10^{23}}$ carbon atoms. $6.022 \times {10^{23}}$ is Avogadro's number.
Also, one mole of any substance contains $6.022 \times {10^{23}}$ ions or atoms or molecules of the substance.
Thus, option (C) is correct.
Also, one mole of an ideal gas occupies a volume of $22.4{\text{ L}}$ at STP i.e. standard temperature and pressure.
Thus, option (D) is not correct.
Thus, mole can be defined as the number of particles contained in $12{\text{ g}}$ of ${\text{C}}$ of atomic mass 12.
Thus, the correct option is (C) number of particles contained in $12{\text{ g}}$ of ${\text{C}}$ of atomic mass 12.

Thus, the correct option is (C)

Note: The mole is defined as the Avogadro’s number which is equal to $6.022 \times {10^{23}}$. The number of entities like ions or atoms or molecules in one mole is the same for all the substances irrespective of the molecular weight or nature of the substance.