Test: Mole Concept & Molar Mass (April 19) - NEET MCQ

(A): Zn + 2HCl → ZnCl₂ + H₂
1 mole of Zn produces 2 g of H₂
0.5 mole of Zn will produce 1 g of H₂
(B): C₇₀H₂₂
Molar mass - 862
Mass of atoms = 862/6.023 x 10²³ = 1.43 x 10^-21 g
(C): 70 g of CI₂ = 6.023 x 10²³ molecules
35.5 g of CI₂ = 3.01 x 10²³ molecules
(D): Molar mass of SO₂ = 64 = 1 mole
64 g of SO₂ = 6.023 x 10²³ molecules

1 mole occupies a volume of 22.4 L at STP
Mass of 1 mole of a gas = Density x Volume
= 1.78 x 22.4 = 39.9 g

Number of molecules of gas at STP
 molecules
Number of atoms in diatomic molecule
= 2 x 7.5 x 10²² = 15 x 10²² atoms

One molecule of sugar (C₁₂H₂₂O₁₁) = 45 atoms
Number of moles of sugar = 1000/342 = 2.92
Number of molecules = 2.92 x 6.023 x 10²³
= 17.60 x 10²³
molecules Number of atoms = 45 x 17.60 x 10²³ 
= 7.92 x 10²⁵ atoms

Standard  molar volume is the volume occupied by 1 mole of a gas at STP.
0.1784 g of He occupies volume = 1 L
4 g (1 mole) of He occupies 4/0.1784 = 22.4 L

(A) 28 gof He = 28/4 = 7mol
(B) 46 g of Na = 46/23 = 2 mol
(C) 60 g of Ca = 60/40 = 1.5 mol
(D) 27 g of Al = 27/27 = 1 mol

18g of H₂O = 1 mol
180 g of H₂O = 10 mol
18 g of H₂O = 6.023 x 10²³ molecules of H₂O
180 g of H₂O = = 6.023 x 10²⁴ molecules of H₂O

1 mole of CO₂ = 44 g
88 g of CO₂ = 2 moles
No. of oxygen atoms in 2 moles = 2 x 2 x N_A
= 2 x 2 x 6.023 x 10²³ = 24.08 x 10²³

Atomic mass of an element
= Mass of one atom x N_A
= 3.32 x 10^-23 x 6.023 x 10²³ = 19.99 = 20 g
No. of gram atoms

Explanation for the Term Molar Mass:
Definition: Molar mass is defined as the mass of one mole of a particular substance. It is usually expressed in grams per mole (g/mol).

Concept of Mole: A mole is a unit in chemistry that is used to express amounts of a chemical substance. It is defined as the amount of any substance that contains as many entities (e.g., atoms, molecules, ions, electrons) as there are atoms in 12 grams of pure carbon-12.

Calculation of Molar Mass:
The molar mass is calculated by summing the masses of all the atoms in a molecule. For instance, the molar mass of water (H₂O) is calculated by adding the molar masses of hydrogen and oxygen.

Difference from Other Terms:
Molar mass is different from molecular mass, Avogadro's mass, and formula mass. Molecular mass refers to the mass of a single molecule, measured in atomic mass units (amu). Avogadro's mass is a deprecated term that was used to refer to the molar mass of carbon-12. And formula mass refers to the sum of the atomic weights of the atoms in the empirical formula of any compound.

Usage: The concept of molar mass is fundamental in chemistry, as it connects the macroscopic world (scale of grams, liters, etc.) with the microscopic one (scale of atoms, molecules, etc.). It is used in various calculations such as stoichiometry, gas laws, and solution preparation.