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 isotope.
(D) The number of molecules in 22.4 litres of a gas STP.
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. NA and it is given as 6.023×1023.
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 NA 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, one mole of a gas is equal to the number of molecules contained in 12 grams pf12C isotope.
112C atom =12.000u 1 mole of 12C atoms =12.000g
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 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}.