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

Molar mass of O₂ = 32 g mol^-1
32 g of O₂ = 6.023 x 10²³ molecules
40 g of O₂ =  = 7.529 x 10²³ molecules
Mass of 6.023 x 10²³ molecules of CO₂ = 44 g
Mass of 7.529 x 10²³ molecules of CO₂

(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

One molecule of oxalic acid dihydrate (COOH)₂ 2H₂O contains 6 oxygen atoms.
Number of oxygen atoms in 1 mole = 6 x 6.023 x 10²³ = 36.13 x 10²³ atoms

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 moles ∝ 1/Molecular mass Molecular mass of CO₂ = 44, N₂ = 28, CH₄ = 16, HCl = 36.5
CO₂ will have least volume, as no. of moles is directly proportional to volume at constant P and T.

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

No. of moles of 34 g of NH₃ = 34/17 = 2
No. of molecules = 2 x 6.023 x 10²³
No. of atoms in one molecule of NH₃ = 4
No. of atoms in 2 molecules of NH₃
= 4 x 2 x 6.023 x 10²³ = 48.18 x 10²³

Number of gram atoms of H

Mass of hydrogen atoms = 1 x 1.66 x 10^-22
= 1.66 x 10^-22 g

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

2H₂O → 2H₂ + O₂
2 x 18 = 36g
36 g of water produces 1 mole of O₂ gas.
180 g of water will produce 180/36 = 5 moles of O₂ gas.

No. of atoms in 1 mole of PCI₃ = 4
No. of atoms in 1.4 moles of PCI₃
= 4 x 1.4 x 6.022 x 10²³ = 3.372 x 10²⁴

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

Volume of gas in 1 L = 0.06/100 = 6 x 10^-4 L
Number of molecules of CO₂ = n x N_A
6 x 10^-4/22.4 x 6.023 x 10²³ = 1.61 x 10¹⁹

No. of O atoms in CO₂ = 2
Molar mass of CO₂ = 44 g
44 g = 1 mol ⇒ 22 g = 0.5 mol
1 mole of CO₂ contains = 2 x 6.023 x 10²³ O atoms
0.5 mole of CO₂ = 6.023 x 10²³ O atoms
1 mole of CO = 6.023 x 10²³ O atoms
Mass of 1 mole of CO = 12 + 16 = 28 g

(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

Mass of AI₂O₃ = 2 x 27 + 3 x 16 = 102
0.051 g of AI₂O₃ = 0.051/102 = 0.0005 mol
1 mol of AI₂O₃ contains 2 x 6.023 x 10²³ Al³⁺ ions
0.0005 mol of AI₂O₃ contains 2 x 0.0005 x 6.023 x 10²³
Al³⁺ ions = 6.023 x 10²⁰ Al³⁺ ions

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

6CaO + P₄O₁₀ → 2Ca₃(PO₄)₂
1 mole of P₄O₁₀ = molar mass, of P₄O₁₀ = 284g
852 g of P₄O₁₀ = 852/284 = 3mol
1 mole of P₄O₁₀ reacts with.6 moles of CaO
3 moles of P₄O₁₀ reacts with 18 moles of CaO Mass of 18 moles of CaO = 18 x 56 = 1008 g

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

2 g of H₂ = 1 mole, 32 g of O₂ = 1 mole
Total volume of 2 moles of gases at NTP = 2 x 22.4 L
= 44.8L

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

1 mole = 6.023 × 10²³ atoms / molecules = X
1 mole = Molar volume =22.4 L at NTP = Y
1 mole = Gram atomic mass or gram molecular mass = Z
Hence, option B is correct.

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.

1 mole of CH₄ = 16 g
16 g of CH₄ contain 10 electrons
1.6 g of CH₄ contain 10/16 x 1.6 x 6.023 x 10²³ 
= 6.023 x 10²³ electrons