Some Basic Concepts of Chemistry

1. The SI unit of amount of substance is:

• a) Gram
• b) Mole ✅
• c) Kilogram
• d) Atom

2. Avogadro number is equal to:

• a) 3.14 × 10⁷
• b) 1.6 × 10^-19
• c) 6.022 × 10²³ ✅
• d) 9.11 × 10^-31

3. 1 mole of oxygen gas (O2) contains how many oxygen atoms?

• a) 6.022 × 10²³
• b) 1.2044 × 10²⁴ ✅
• c) 3.011 × 10²³
• d) 6.022 × 10²²

4. The molar mass of H₂SO₄ (sulfuric acid) is approximately:

• a) 49 g/mol
• b) 98 g/mol
• c) 98.08 g/mol ✅
• d) 65 g/mol

5. Law of definite proportions states that a chemical compound always contains the same elements in:

• a) Fixed mass ratio ✅
• b) Variable mass ratio
• c) Fixed volume ratio
• d) Variable atomic ratio

6. Empirical formula gives:

• a) Actual number of atoms in molecule
• b) Simplest whole number ratio of atoms ✅
• c) Molecular mass
• d) Structural formula

7. The molar volume of an ideal gas at STP (0°C, 1 atm) is:

• a) 11.2 L
• b) 22.4 L ✅
• c) 24.0 L
• d) 18.0 L

8. If 2.0 g of H₂ react with O₂, how many moles of H₂ are present? (Molar mass H = 1 g/mol)

• a) 1.0 mol ✅
• b) 2.0 mol
• c) 0.5 mol
• d) 0.25 mol

9. Percentage composition by mass refers to:

• a) Percentage of volume of each element
• b) Mass of each element per 100 g of compound ✅
• c) Number of atoms of each element
• d) Moles of each element

10. Mole fraction is defined as:

• a) moles of solute per litre
• b) moles of solute per kg solvent
• c) moles of component / total moles of mixture ✅
• d) mass of component / total mass

11. Limiting reagent in a reaction is:

• a) Reactant present in excess
• b) Reactant that is completely consumed first ✅
• c) Product formed in least amount
• d) Catalyst

12. Normality (N) is defined as:

• a) moles of solute per litre
• b) equivalents per litre ✅
• c) mass percent
• d) mole fraction

13. The molecular formula of hydrogen peroxide is:

• a) HO
• b) H₂O₂ ✅
• c) H₂O
• d) H₃O

14. A 1.0 M solution contains:

• a) 1 mole solute per kg solvent
• b) 1 mole solute per litre solution ✅
• c) 1 mole solute per 100 g solution
• d) 1 equivalent per litre

15. Empirical formula of a compound with composition 40% C, 6.7% H and 53.3% O is:

• a) CHO
• b) CH₂O ✅
• c) C₂H₄O
• d) C₃H₆O

16. If 4 moles of A react to give 8 moles of B, the stoichiometric coefficient ratio B:A is:

• a) 2:1 ✅
• b) 1:2
• c) 4:8
• d) 1:1

17. Equivalent weight of an acid is:

• a) molar mass × valency
• b) molar mass / basicity ✅
• c) molar mass / valency
• d) inverse of molar mass

18. The law of conservation of mass was given by:

• a) Dalton
• b) Lavoisier ✅
• c) Avogadro
• d) Gay-Lussac

19. Mass percent of Na in NaCl (Na = 23, Cl = 35.5) is approximately:

• a) 39%
• b) 39.34% ✅
• c) 60.66%
• d) 23%

20. Molecule with atomicity 3 is:

• a) O₂
• b) O₃ ✅
• c) N₂
• d) H₂O

21. Avogadro's hypothesis relates equal volumes of gases to equal number of:

• a) Atoms
• b) Molecules ✅
• c) Grams
• d) Electrons

22. 44 g of CO₂ contains how many moles? (Molar mass CO₂=44 g/mol)

• a) 1.0 mol ✅
• b) 0.5 mol
• c) 2.0 mol
• d) 11 mol

23. ppm stands for:

• a) parts per million ✅
• b) parts per milli
• c) percent per million
• d) parts per meter

24. In a balanced chemical equation, coefficients represent:

• a) Mass ratio
• b) Mole ratio ✅
• c) Volume ratio
• d) Empirical ratio

25. The oxidation number of oxygen in most compounds is:

• a) +2
• b) -2 ✅
• c) -1
• d) 0

26. A solution made by diluting 2 M solution to double the volume becomes:

• a) 1 M ✅
• b) 4 M
• c) 0.5 M
• d) 2 M

27. The formula weight of ionic compounds is usually called:

• a) Formula mass ✅
• b) Molecular mass
• c) Atomic mass
• d) Equivalent mass

28. If empirical formula is CH₂ and molar mass is 56 g/mol, molecular formula is:

• a) C₂H₄
• b) C₄H₈ ✅
• c) C₃H₆
• d) C₆H₁₂

29. The gas constant R in PV = nRT has units:

• a) L·atm·mol⁻¹·K⁻¹ ✅
• b) J·mol⁻¹
• c) atm·mol⁻¹
• d) K·mol·L⁻¹

30. Which is a strong electrolyte?

• a) Acetic acid
• b) HCl ✅
• c) Glucose
• d) Methanol

31. A sample contains 3.011 × 10²³ particles. This many particles correspond to:

• a) 0.2 mol
• b) 0.5 mol ✅
• c) 1.0 mol
• d) 2.0 mol

32. In titration, the point at which equivalent amounts have reacted is called:

• a) Equivalence point ✅
• b) End point
• c) Neutralization point
• d) Titration point

33. Atomic mass unit (u) is approximately equal to:

• a) 1 g
• b) 1.6605 × 10^-24 g ✅
• c) 1.6605 × 10^-27 g
• d) 1.6605 × 10^-21 g

34. A hydrate with formula CuSO₄·5H₂O has how many moles of water per mole of salt?

• a) 1
• b) 5 ✅
• c) 4
• d) 10

35. Ionic bond is formed by:

• a) Transfer of electrons ✅
• b) Sharing of electrons
• c) Metallic bonding
• d) Hydrogen bonding

36. Mass of 0.25 mol of NaCl (M = 58.44 g/mol) is approximately:

• a) 14.61 g ✅
• b) 58.44 g
• c) 29.22 g
• d) 7.31 g

37. The term 'stoichiometry' primarily deals with:

• a) Reaction rates
• b) Quantitative relations in reactions ✅
• c) Chemical equilibrium
• d) Thermodynamics

38. Which of the following is NOT a unit of concentration?

• a) Molarity
• b) Molality
• c) Avogadro ✅
• d) Normality

39. The relative atomic mass of chlorine (Cl) considering isotopes 35 and 37 is approximately 35.5. This value is called:

• a) Atomic number
• b) Atomic mass (relative) ✅
• c) Mass number
• d) Valency

40. In which ratio is oxygen present in water by mass? (H = 1, O = 16)

• a) 1:8
• b) 8:1 ✅
• c) 16:2
• d) 2:16

41. Percent yield is calculated as:

• a) (Actual / Theoretical) × 100 ✅
• b) (Theoretical / Actual) × 100
• c) Actual − Theoretical
• d) Theoretical − Actual

42. Molecular mass of glucose C₆H₁₂O₆ is approximately (C=12,H=1,O=16):

• a) 180 g/mol ✅
• b) 190 g/mol
• c) 150 g/mol
• d) 170 g/mol

43. Which quantity remains constant for all gases at the same temperature and pressure according to Avogadro?

• a) Mass
• b) Number of molecules per unit volume ✅
• c) Density
• d) Molar mass

44. The empirical formula of a compound is CH₃O. Its molar mass is 60 g/mol. The molecular formula is:

• a) C₂H₆O₂
• b) C₂H₆O ✅
• c) C₃H₉O
• d) C₄H₁₂O

45. Which of the following is a covalent compound?

• a) CO₂ ✅
• b) NaCl
• c) MgO
• d) KCl

46. A compound has 40% S and 60% O by mass. Its empirical formula is:

• a) SO
• b) SO₂ ✅
• c) S₂O
• d) S₂O₃

47. Which instrument is used to determine relative molecular masses by measuring mass-to-charge ratio?

• a) Mass spectrometer ✅
• b) Spectrophotometer
• c) Chromatograph
• d) Calorimeter

48. A 0.1 molal solution contains 0.1 mole solute per:

• a) litre of solution
• b) kg of solvent ✅
• c) 100 g solution
• d) mol of solvent

49. Which of the following shows law of multiple proportions?

• a) H₂O and H₂O₂
• b) CO and CO₂ ✅
• c) NaCl and KCl
• d) CH₄ and C₂H₆

50. The statement "Equal numbers of molecules of all gases occupy equal volumes at same T and P" is known as:

• a) Avogadro's law ✅
• b) Boyle's law
• c) Charles' law
• d) Gay-Lussac's law