Some Basic Concepts of Chemistry

What you'll learn

A patient, from-scratch guide to the mole, Avogadro's number, molar mass, empirical vs molecular formulas and stoichiometry — with fully worked numericals aligned to the NCERT Class 11 syllabus.

This chapter has

Some Basic Concepts of Chemistry — solved practice questions

8 Class 11 Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   How many significant figures are there in the measurement 0.00520?

   • A2
   • B3
   • C4
   • D5
   Show answer & solution

   Correct answer: (B) 3

   Leading zeros are not significant, but the trailing zero after the decimal point is. So 5, 2 and 0 are significant, giving 3 significant figures.

2. Q2easy

   The SI base unit for the amount of substance is the:

   • Akilogram
   • Bkelvin
   • Cmole
   • Dcandela
   Show answer & solution

   Correct answer: (C) mole

   Amount of substance is measured in the mole (mol), which is one of the seven SI base units.

3. Q3easy

   The molar mass of carbon dioxide (CO2) is (C = 12, O = 16):

   • A44 g/mol
   • B28 g/mol
   • C32 g/mol
   • D46 g/mol
   Show answer & solution

   Correct answer: (A) 44 g/mol

   Molar mass of CO2 = 12 + 2 x 16 = 12 + 32 = 44 g/mol.

4. Q4medium

   How many moles are present in 11 g of CO2? (Molar mass of CO2 = 44 g/mol)

   • A1 mol
   • B0.75 mol
   • C0.5 mol
   • D0.25 mol
   Show answer & solution

   Correct answer: (D) 0.25 mol

   Number of moles = given mass / molar mass = 11 / 44 = 0.25 mol.

5. Q5easy

   The number of particles present in one mole of a substance (Avogadro's number) is approximately:

   • A6.022 x 10^22
   • B3.011 x 10^23
   • C6.022 x 10^23
   • D1.2 x 10^24
   Show answer & solution

   Correct answer: (C) 6.022 x 10^23

   One mole contains Avogadro's number of particles, which is 6.022 x 10^23.

6. Q6easy

   The statement that mass can neither be created nor destroyed in a chemical reaction is known as the:

   • ALaw of definite proportions
   • BLaw of conservation of mass
   • CLaw of multiple proportions
   • DGay-Lussac's law of gaseous volumes
   Show answer & solution

   Correct answer: (B) Law of conservation of mass

   This is the Law of Conservation of Mass, proposed by Antoine Lavoisier, stating total mass of reactants equals total mass of products.

7. Q7medium

   The empirical formula of glucose (molecular formula C6H12O6) is:

   • ACH2O
   • BC6H12O6
   • CCHO
   • DC2H4O2
   Show answer & solution

   Correct answer: (A) CH2O

   Dividing the subscripts by their highest common factor 6 gives the simplest whole-number ratio C:H:O = 1:2:1, so the empirical formula is CH2O.

8. Q8medium

   The mass percent of nitrogen in ammonia (NH3) is (N = 14, H = 1):

   • A17.65%
   • B46.67%
   • C25%
   • D82.35%
   Show answer & solution

   Correct answer: (D) 82.35%

   Mass % of N = (mass of N / molar mass of NH3) x 100 = (14 / 17) x 100 = 82.35%.

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