Solveeit Logo

Question

Question: One mole of a gas refers to: (A) The number of molecules in one litre of gas. (B) The number of ...

One mole of a gas refers to:
(A) The number of molecules in one litre of gas.
(B) The number of molecules in one gram of gas.
(C) The number of molecules contained in 12 grams of 12C{ }^{12} \mathrm{C} isotope.
(D) The number of molecules in 22.4 litres of a gas STP.

Explanation

Solution

According to STP, the molar volume of a gas is the volume of one mole of a gas. At STP, one mole of any gas occupies 22.4 litres of volume. One mole of a gas is given by the
Avogadro's number i.e. NAN_{A} and it is given as 6.023×10236.023 \times 10^{23}.

Complete step-by-step answer:
- Discussing option A, one mole of a gas does not refer to the number of molecules in one litre of
gas. Because there are not NAN_{A} numbers of molecules in one litre of gas.
- Discussing option B, one mole of a gas is never equal to 1gm of gas. Because it is equal to molar mass. A mole of atoms of any gas has a mass in grams equal to the atomic weight of the gas.
- Discussing the option C\mathrm{C}, one mole of a gas is equal to the number of molecules contained in 12 grams pf12C\mathrm{pf}^{12} \mathrm{C} isotope.
112C atom =12.000u 1 mole of 12C atoms =12.000g \begin{array}{l} 1^{12} \mathrm{C} \text { atom }=12.000 \mathrm{u} \\\ 1 \text { mole of }{ }^{12} \mathrm{C} \text { atoms }=12.000 \mathrm{g} \end{array}
Thus,
1 mol of a gas = atomic weight of that gas.
- Discussing option D, One mole of a gas refers to the number of molecules in 22.4 litres of a gas STP. At STP, all the gas has 22.4 L22.4 \ \mathrm{L} in 1 mole. This is a standard value decided by the IUPAC.
Clearly, the answers are C and D.

Note: Mole concept is one of the most fundamental topics in chemistry. This is because it forms the number of elementary particles in a sample of a pure substance by determining the mass of the sample. 1 mole of any substance contains Avogadro constant number of particles i.e., 6.023 \times 10^{23}.