Mole — Avogadro number, molar mass
Mole Concept
4
JEE Qs
8%
Hard
75
min
Master the interconversion among mass, moles, and number of particles using molar mass and Avogadro's number; unit consistency and clear definition of the particle are paramount.
🧮 Key Formulas
✅ Key Points for JEE
- 1A mole is a specific quantity, 6.022 x 10^23 entities (Avogadro's number, N_A), acting as a bridge between the macroscopic mass and microscopic number of particles.
- 2Molar mass (M) is the mass of one mole of a substance in grams per mole (g/mol), numerically equal to its atomic, molecular, or formula mass in atomic mass units (amu).
- 3Avogadro's number is a universal constant used to convert between moles and the actual number of atoms, molecules, ions, electrons, or any other specified entity.
- 4Always pay close attention to units (g, mol, g/mol) and the specific entity being counted (atoms, molecules, ions) to avoid common calculation errors.
⚠️ Common Mistakes
- ✕Confusing atomic/molecular mass in amu with molar mass in g/mol; while numerically equal, their units and contexts differ.
- ✕Incorrectly applying Avogadro's number (multiplying when division is needed, or vice-versa) when converting between moles and number of particles.
- ✕Errors in calculating molar mass of compounds by not summing atomic masses correctly or forgetting to multiply atomic masses by their respective subscripts in the chemical formula.
- ✕Not distinguishing between the number of moles of molecules and the number of moles of atoms within those molecules (e.g., 1 mole of H2O contains 2 moles of H atoms and 1 mole of O atoms).
📝 Practice Questions
See allQ71.Xg of benzoic acid on reaction with aq NaHCO3 released CO2 that occupied 11.2 L volume at STP. X is _____ g.
Q60.The elemental composition of a compound is 54.2%C, 9.2%H and 36.6%O. If the molar mass of the compound is 132 g mol−1 , the molecular formula of the compound is : [Given : The relative atomic mass of C : H : O = 12 : 1 : 16 ] (1) C4H9O3 (2) C6H12O6 (3) C4H8O2 (4) C6H12O3
Q67.Match the LIST-I with LIST-II Choose the correct answer from the options given below: (1) A-II, B-I, C-III, D-IV (2) A-II, B-III, C-I, D-IV (3) A-IV, B-I, C-III, D-II (4) A-IV, B-III, C-I, D-II
Q73.When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the mass of aluminium oxide produced in grams is_______ - (Nearest integer) Given : Molar mass of Al is 27.0 g mol−1 Molar mass of O is 16.0 g mol−1
Q72.Consider the following reaction occurring in the blast furnace: Fe3O4( s) + 4CO(g) →3Fe(l) + 4CO2( g) ' x ' kg of iron is produced when 2.32 × 103 kgFe3O4 and 2.8 × 102 kgCO are brought together in the furnace. The value of ' x ' is _____. (nearest integer) Given: molar mass of Fe3O4 = 232 g mol−1 molar mass of CO = 28 g mol−1 molar mass of Fe = 56 g mol−1} Q73. 37.8 g N2O5 was taken in a 1 L reaction vessel and allowed to undergo the following reaction at 500 K 2 N2O5( g) ⇌2 N2O4( g) + O2( g) The total pressure at equilibrium was found to be 18.65 bar. Then, Kp = ______ ×10−2 [nearest integer] Assume N2O5 to behave ideally under these conditions. Given: R = 0.082 bar Lmol−1 K−1
Q31.Combustion of glucose (C6H12O6) produces CO2 and water. The amount of oxygen (in g) required for the complete combustion of 900 g of glucose is : [Molar mass of glucose in gmol−1 = 180 ] (1) 480 (2) 800 (3) 960 (4) 32
NCERT Chapters
- Class 11 Chemistry Ch 1: Some Basic Concepts of Chemistry