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9th – Chemistry – Chapter 4 – Stoichiometry

October 8, 2026 · Blog

MCQs

  1. What is the molecular formula of a compound having the empirical formula CH₂O and a molar mass of 180 g/mol?
    a) CH₂O b) C₂H₄O₂ c) C₆H₁₂O₆ d) C₃H₆O₃
  2. Which of the following equations represents a reversible reaction?
    a) 2H₂ + O₂ → 2H₂O b) N₂ + 3H₂ ⇌ 2NH₃ c) 2Na + Cl₂ → 2NaCl d) 2Mg + O₂ → 2MgO
  3. When one mole of each substance is completely burned in oxygen, which produces the greatest amount of CO₂?
    a) Carbon b) Diamond c) Ethane (C₂H₆) d) Methane (CH₄)
  4. How much CaCl₂ is produced when 25 g of CaCO₃ reacts with excess HCl?
    a) 27.75 g b) 55.5 g c) 111 g d) 222 g
  5. A diamond necklace contains 6 g of carbon. Approximately how many carbon atoms does it contain?
    a) 6.02 × 10²³ b) 12.04 × 10²³ c) 1.003 × 10²³ d) 3.01 × 10²³
  6. How many moles of oxygen are required to react with 0.3 moles of aluminium?
    a) 0.225 moles b) 0.45 moles c) 0.6 moles d) 0.9 moles
  7. Which equation correctly represents the complete combustion of ethanol?
    a) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O b) C₂H₅OH + 3O₂ → 2CO₂ + 2H₂O c) C₂H₅OH + 2O₂ → CO₂ + H₂O d) C₂H₅OH + O₂ → 2CO₂ + H₂O
  8. What is the charge on a sodium ion?
    a) 1⁺ b) 2⁺ c) 1⁻ d) 2⁻
  9. What is Avogadro’s number?
    a) 6.022 × 10²² b) 6.022 × 10²⁴ c) 6.022 × 10²¹ d) 6.022 × 10²³
  10. What is the correct chemical formula for calcium phosphide?
    a) CaP b) CaP₂ c) Ca₂P₃ d) Ca₃P₂
  11. What state symbol represents ammonia in the equation N₂ + 3H₂ ⇌ 2NH₃?
    a) (s) b) (l) c) (g) d) (aq)
  12. According to 2H₂ + O₂ → 2H₂O, how many moles of water are produced when 4 moles of hydrogen react completely?
    a) 1 mole b) 2 moles c) 4 moles d) 8 moles
  13. One mole of CH₄ contains:
    a) 12 g of carbon b) 18 g of hydrogen c) 36 g of oxygen d) 6.022 × 10²³ molecules
  14. What mass of CaCl₂ is produced when 100 g of CaCO₃ reacts with excess HCl?
    a) 111 g b) 222 g c) 55.5 g d) 27.75 g
  15. What is the chemical formula of magnesium nitride?
    a) MgN b) Mg₂N₃ c) Mg₃N₂ d) MgN₂
  16. What is the molar mass of glucose, C₆H₁₂O₆?
    a) 180 g/mol b) 160 g/mol c) 140 g/mol d) 120 g/mol
  17. How many moles of CO₂ are produced when 1.8 moles of ethanol burn completely?
    a) 1.8 moles b) 3.6 moles c) 5.4 moles d) 7.2 moles
  18. The term “molar mass” refers to:
    a) The weight of one atom b) The number of atoms in a molecule c) The volume of one mole d) The mass of one mole of a substance
  19. What is the empirical formula of a compound with molecular formula C₂H₂?
    a) CH₂ b) C₂H₄ c) CH d) C₂H₆
  20. Why is the mole concept important in chemistry?
    a) It determines the colour of substances b) It measures temperature c) It determines reaction speed d) It allows atoms and molecules to be counted through measurable amounts of matter
  21. What is the molar mass of CO₂?
    a) 28 g/mol b) 32 g/mol c) 44 g/mol d) 56 g/mol
  22. What is the empirical formula of benzene, C₆H₆?
    a) C₆H₆ b) CH c) C₃H₃ d) C₂H₂
  23. What is the empirical formula of 2-hexene, CH₃–CH=CH–(CH₂)₂–CH₃?
    a) C₂H₂ b) CH c) C₆H₁₂ d) CH₂
  24. What is the molecular formula of a compound whose empirical formula is CH and molar mass is 78 g/mol?
    a) CH b) C₂H₂ c) C₆H₆ d) C₃H₃
  25. What is the mass of one mole of NaCl?
    a) 23 g b) 44 g c) 96 g d) 58.5 g
  26. According to 2C + O₂ → 2CO, how many grams of CO are produced from 24 g of carbon?
    a) 24 g b) 44 g c) 56 g d) 12 g
  27. What does the symbol (g) represent in a chemical equation?
    a) Aqueous solution b) Solid c) Liquid d) Gas
  28. How many grams of CO₂ are produced when 100 g of CaCO₃ reacts with excess HCl?
    a) 44 g b) 88 g c) 132 g d) 176 g
  29. What is the molar mass of H₂SO₄?
    a) 98 g/mol b) 180 g/mol c) 58.5 g/mol d) 44 g/mol
  30. Which compound has the highest percentage of nitrogen by mass?
    a) CO(NH₂)₂ b) N₂H₄ c) NH₃ d) NH₂OH
  31. How many grams of water are produced when 100 g of CaCO₃ reacts with excess HCl?
    a) 18 g b) 36 g c) 54 g d) 72 g
  32. Which equation correctly represents the reversible formation of ammonia?
    a) N₂ + 3H₂ → 2NH₃ b) N₂ + 3H₂ ⇌ 2NH₃ c) 2NH₃ → N₂ + 3H₂ d) 2NH₃ ⇌ N₂ + 3H₂
  33. What is the total mass of products when 100 g of CaCO₃ reacts with excess HCl?
    a) 173 g b) 273 g c) 373 g d) 473 g
  34. What is the molar mass of carbon monoxide, CO?
    a) 28 g/mol b) 32 g/mol c) 44 g/mol d) 56 g/mol
  35. What is the empirical formula of C₆H₆?
    a) C₆H₆ b) CH c) C₃H₃ d) C₂H₂
  36. What is the total mass of reactants when 100 g of CaCO₃ reacts with excess HCl?
    a) 173 g b) 273 g c) 373 g d) 473 g
  37. What does the symbol (aq) represent?
    a) Aqueous solution b) Solid c) Liquid d) Gas
  38. What is the correct formula for lithium oxide?
    a) LiO b) LiO₂ c) Li₂O d) Li₃O
  39. How many moles are present in 24 g of carbon?
    a) 1 mole b) 2 moles c) 3 moles d) 4 moles
  40. What is the empirical formula of hydrogen peroxide, H₂O₂?
    a) H₂O₂ b) H₂O c) HO d) O₂H
  41. What is the molar mass of NaCl?
    a) 58.5 g/mol b) 23 g/mol c) 35.5 g/mol d) 40 g/mol
  42. What is the chemical formula of aluminium oxide?
    a) AlO b) Al₂O₃ c) Al₃O₂ d) AlO₂
  43. Which compound has the same empirical and molecular formulas?
    a) Benzene (C₆H₆) b) Hydrogen peroxide (H₂O₂) c) Water (H₂O) d) Acetylene (C₂H₂)
  44. How many molecules of water are produced when 5 g of hydrogen reacts with excess oxygen?
    a) 1.505 × 10²⁴ b) 3.01 × 10²⁴ c) 6.022 × 10²³ d) 12.04 × 10²³
  45. A balanced chemical equation follows which law?
    a) Law of multiple proportions b) Periodic law c) Law of definite proportions d) Law of conservation of mass
  46. What is the molar mass of oxygen molecules, O₂?
    a) 16 g/mol b) 48 g/mol c) 64 g/mol d) 32 g/mol
  47. What is the molar mass of hydrogen molecules, H₂?
    a) 1.008 g/mol b) 2.016 g/mol c) 3.024 g/mol d) 4.032 g/mol
  48. What is the crisscross method mainly used for?
    a) Balancing equations b) Finding molecular mass c) Determining empirical formulas d) Writing chemical formulas of ionic compounds
  49. If 100 g of CaCO₃ reacts with excess HCl, how much CaCl₂ is produced?
    a) 50 g b) 111 g c) 200 g d) 44 g
  50. Which is the balanced equation for aluminium reacting with oxygen?
    a) 2Al + 3O₂ → 2Al₂O₃ b) 4Al + 3O₂ → 2Al₂O₃ c) Al + O₂ → Al₂O₃ d) 2Al + O₂ → Al₂O₃
  51. Which scientist is associated with the concept of Avogadro’s number?
    a) Dalton b) Bohr c) Avogadro d) Rutherford
  52. What state symbol represents water in a chemical equation?
    a) (s) b) (l) c) (g) d) (aq)
  53. What is the molar mass of hydrogen atoms?
    a) 1.008 g/mol b) 2.016 g/mol c) 3.024 g/mol d) 4.032 g/mol
  54. Which is the correct formula for calcium chloride?
    a) CaCl b) Ca₂Cl c) CaCl₂ d) Ca₂Cl₂
  55. Which symbol represents a reversible reaction?
    a) → b) = c) ⇌ d) ≠
  56. What is the formula of aluminium oxide?
    a) AlO b) Al₂O₃ c) Al₃O₂ d) AlO₂
  57. Approximately how many atoms are present in one mole of carbon?
    a) 6.022 × 10²² b) 6.022 × 10²³ c) 6.022 × 10²¹ d) 6.022 × 10²⁴
  58. In a reversible reaction, what happens to reactants and products?
    a) Reactants are converted only into products b) Products are converted only into reactants c) Both remain unchanged d) Reactants and products are continuously converted into one another
  59. What does the symbol (l) represent in a chemical equation?
    a) Aqueous solution b) Solid c) Liquid d) Gas
  60. What mass of water is produced when 5 g of hydrogen reacts with excess oxygen?
    a) 18 g b) 36 g c) 45 g d) 12 g
  61. What mass of aluminium is present in 204 g of Al₂O₃?
    a) 26 g b) 27 g c) 54 g d) 108 g
  62. What does the equation Zn + H₂SO₄ → ZnSO₄ + H₂ show?
    a) Zinc reacts with oxygen b) Zinc displaces hydrogen c) Zinc forms a precipitate d) Sulfuric acid is reduced
  63. What is the state symbol for a gaseous substance?
    a) (aq) b) (l) c) (s) d) (g)
  64. Which group contains elements that exist as discrete molecules?
    a) Na, Ca, Fe b) O₂, N₂, H₂ c) Zn, Cu, Ag d) Al, Mg, Si
  65. How many moles are present in 25 g of H₂SO₄?
    a) 0.765 moles b) 0.51 moles c) 0.255 moles d) 0.4 moles
  66. What is the molecular formula of water?
    a) H₁O b) H₂O c) H₂O₂ d) H₃O
  67. What is the molar mass of sulfuric acid, H₂SO₄?
    a) 98 g/mol b) 96 g/mol c) 94 g/mol d) 92 g/mol
  68. What mass of 95% pure CaCO₃ is needed to neutralize 50 cm³ of 0.5 M HCl?
    a) 9.5 g b) 1.25 g c) 1.32 g d) 1.45 g
  69. What is the empirical formula of glucose, C₆H₁₂O₆?
    a) C₆H₁₂O₆ b) C₂H₄O₂ c) CHO d) CH₂O
  70. What is the chemical formula of lithium oxide?
    a) LiO b) Li₂O c) LiO₂ d) Li₂O₂
  71. One mole of any substance contains:
    a) 6.022 × 10²³ molecules or particles b) 1.00 × 10²³ molecules c) 3.011 × 10²³ molecules d) 10.022 × 10²³ molecules
  72. What is the molecular formula of a compound with empirical formula CH₂O and molar mass 60 g/mol?
    a) CH₂O b) C₂H₄O₂ c) C₃H₆O₃ d) C₄H₈O₄
  73. Which symbol represents a reversible reaction?
    a) → b) ↔ c) ← d) ⇌
  74. How many grams of O₂ are required to react with 0.3 moles of aluminium according to 4Al + 3O₂ → 2Al₂O₃?
    a) 4.2 g b) 6.4 g c) 7.2 g d) 10.2 g
  75. What does the symbol (s) represent in a chemical equation?
    a) Aqueous solution b) Solid c) Liquid d) Gas
  76. What is the empirical formula of a compound with molecular formula H₂O₂?
    a) H₂O₂ b) HO c) H₃O d) H₂O
  77. Which represents the empirical formula of hydrogen peroxide?
    a) H₂O₂ b) HO c) H₃O d) H₂O
  78. What is the chemical formula of ozone?
    a) O₂ b) O₃ c) O₄ d) O
  79. What mass of oxygen is required to react with 0.3 moles of aluminium?
    a) 7.2 g b) 14.4 g c) 21.6 g d) 28.8 g
  80. What is the empirical formula of benzene, C₆H₆?
    a) CH b) C₂H₂ c) C₆H₆ d) CH₂
  81. What is the formula unit of sodium chloride?
    a) NaCl₂ b) Na₂Cl c) NaCl d) Na₂Cl₂
  82. Approximately how many atomic mass units are present in one gram?
    a) 1 amu b) 10²³ amu c) 6.022 × 10²³ amu d) 6.022 × 10²² amu
  83. How many moles of oxygen are required to burn 1.8 moles of ethanol completely?
    a) 1.8 moles b) 3.6 moles c) 5.4 moles d) 7.2 moles
  84. What is the molar mass of phosphoric acid, H₃PO₄?
    a) 98 g/mol b) 96 g/mol c) 94 g/mol d) 92 g/mol
  85. Sodium chloride exists in the form of:
    a) Atoms b) Molecules c) Covalent bonds d) Ions bonded in a crystal lattice
  86. How many atoms are present in one gram of water?
    a) 1.002 × 10²³ atoms b) 6.022 × 10²³ atoms c) 0.334 × 10²³ atoms d) 2.004 × 10²³ atoms
  87. What does Avogadro’s number represent?
    a) The number of grams in one mole b) The number of atoms or molecules in one mole c) The weight of one atom d) The mass of a compound

SHORT QUESTIONS

  1. Calculate the molar mass of CO₂.
  2. Which symbol is used to represent a reversible reaction?
  3. What is the difference between a mole and Avogadro’s number?
  4. How does the mole help us count atoms?
  5. Write the chemical formula of magnesium nitride.
  6. Write the formulas of calcium phosphate, aluminium nitride, sodium acetate, ammonium carbonate, and bismuth sulphate.
  7. Calculate the molar mass of H₂O.
  8. How is the formula of an ionic compound written?
  9. State the relationship between molecular and empirical formulas.
  10. How can the amount of product be calculated from a given reactant?
  11. What information does a balanced chemical equation provide?
  12. How does the mass of reactants compare with the mass of products in a chemical reaction?
  13. Why must a chemical equation be balanced?
  14. Write the balanced chemical equation for the reaction of copper with sulphuric acid to form copper sulphate, sulphur dioxide, and water.
  15. What role does stoichiometry play in determining the amounts of reactants and products?
  16. What is the mass of one mole of carbon atoms?
  17. Why is a balanced chemical equation important?
  18. Define molar mass and give an example.
  19. What happens if a chemical equation is not balanced?
  20. How does the crisscross method ensure neutrality in ionic compounds?
  21. Why is Avogadro’s number important in chemistry?
  22. Define the mole concept.
  23. What is the mole ratio in a balanced chemical equation?
  24. Write the formula of aluminium oxide.
  25. How can the molecular formula be determined from the empirical formula?
  26. Write the chemical formula of barium nitride.
  27. Give two examples of compounds whose empirical and molecular formulas are the same.
  28. Why does increasing the number of reactants not change the reaction ratio?
  29. What is the total mass of reactants when CaCO₃ reacts with HCl?
  30. Why is the mole concept useful in chemical reactions?
  31. Why do ionic compounds generally have empirical formulas rather than molecular formulas?
  32. State the law of conservation of mass.
  33. Sand has the formula SiO₂ but does not exist as separate molecules like H₂O. How is its formula determined?
  34. What is the relationship among moles, mass, and molar mass?
  35. Why is Avogadro’s number extremely important in chemistry?
  36. How many molecules are present in 1.5 g of H₂O?
  37. Define empirical formula with an example.
  38. Define empirical formula.
  39. What is the crisscross method?
  40. What is meant by a reversible reaction?
  41. How does a molecular formula differ from an empirical formula?
  42. A compound weighing 8.657 g contains 5.217 g carbon, 0.962 g hydrogen, and 2.478 g oxygen. Calculate the percentage of each element.
  43. Write the chemical formula of hydrogen peroxide.
  44. How does an empirical formula help identify a compound?
  45. Give examples of covalent compounds along with their molecular formulas.
  46. Explain how different compounds can have the same empirical formula but different molecular formulas.
  47. If one glass contains 400 cm³ of water, how many moles of water are needed for one adult drinking eight such glasses?
  48. Why is knowing the molecular formula of a compound important?
  49. How can the masses of products be calculated in a reversible reaction?
  50. How many molecules are present in one mole of oxygen gas?
  51. What is the empirical formula of hydrogen peroxide, H₂O₂?
  52. How does the empirical formula differ from the molecular formula?
  53. Give an example of a binary ionic compound and write its formula.
  54. Define reactants and products.
  55. How is a chemical equation balanced?
  56. What is the chemical formula of ozone?
  57. Write the formula of lithium oxide.
  58. How are elements represented in chemistry?
  59. Give an example of an element that exists as discrete molecules.
  60. How is a molecular formula determined experimentally?
  61. What is Avogadro’s number?
  62. What is the formula unit of sodium chloride?
  63. Define a chemical equation.
  64. Why should chemical calculations be based on a balanced equation?
  65. Why is stoichiometry important in industrial chemical production?
  66. Why is stoichiometry important in the chemical industry?
  67. What is the significance of the mole in chemistry?
  68. Why must chemical equations be balanced?
  69. What happens when calcium carbonate reacts with hydrochloric acid?
  70. Define molar mass.
  71. What is the empirical formula of benzene, C₆H₆?
  72. What does n represent in the molecular formula equation?
  73. What is the significance of a chemical formula?
  74. Why can some compounds have the same empirical formula but different molecular formulas?
  75. Why does increasing the number of reactant molecules not change their ratio?
  76. What is a molecular formula?
  77. Define stoichiometry.
  78. Find the molecular formula of a compound with empirical formula CH₂O and molar mass 180 g/mol.
  79. How is the molar mass of a compound calculated?
  80. How does the mole concept help in practical chemical reactions?
  81. Why is Avogadro’s number used in chemistry?

LONG QUESTIONS

  1. Explain how the molecular formula of a compound can be determined from its empirical formula, giving suitable examples.
  2. If 1.80 moles of ethanol, C₂H₅OH, are burned in air, calculate the moles of O₂ required and the moles of CO₂ produced.
  3. Calculate the mass of CO produced when 24 g of carbon reacts with excess oxygen.
  4. Define stoichiometry and explain its importance in chemical reactions.
  5. Describe the rules for writing a balanced chemical equation and provide an example.
  6. Calculate the number of molecules present in 36 g of H₂O.
  7. Calculate the mass of oxygen required to react completely with 0.3 moles of aluminium according to 4Al + 3O₂ → 2Al₂O₃.
  8. Calculate the number of H₂O molecules produced when 5 g of hydrogen reacts with excess oxygen.
  9. Calculate the mass of CO₂ produced when 10 g of CH₄ reacts with excess O₂ according to CH₄ + 2O₂ → CO₂ + 2H₂O.
  10. Calculate the mass of ammonia required to produce 1 kg of urea fertilizer according to 2NH₃ + CO₂ → CO(NH₂)₂ + H₂O.
  11. A compound has an empirical formula CH₂O and a molar mass of 60 g/mol. Determine its molecular formula.
  12. What is Avogadro’s number? Explain its significance in chemistry.
  13. Explain the law of conservation of mass with a suitable example.
  14. Explain the crisscross method used for writing formulas of binary ionic compounds.
  15. A compound has empirical formula CH₂ and molar mass 180 g/mol. Determine its molecular formula.
  16. According to 3C + O₂ + H₂O → H₂ + 3CO, calculate the number of moles of carbon required to produce 10 moles of CO.
  17. Explain the concepts of Avogadro’s number and the mole.
  18. A compound has empirical formula CH and molecular mass 78 g/mol. Determine its molecular formula.
  19. Explain the mole concept with suitable examples.
  20. According to 2H₂S + SO₂ → 2H₂O + 3S, calculate the mass of SO₂ required to produce 10 moles of sulfur.
  21. What conditions must be fulfilled before writing a chemical equation for a reaction?
  22. Calculate the molar masses of H₃PO₄, SO₂, Cl₂, H₂O₂, N₂O₄, and MgCO₃.
  23. Define molecular and empirical formulas and explain the differences between them with examples.
  24. Calculate the number of atoms in: (a) 3 g of H₂, (b) 3.4 moles of N₂, and (c) 10 g of C₆H₁₂O₆.
  25. When 25 g of CaCO₃ reacts with excess HCl, calculate the amount of CaCl₂ produced.

ANSWER KEY

  1. c) C₆H₁₂O₆
  2. b) N₂ + 3H₂ ⇌ 2NH₃
  3. c) Ethane (C₂H₆)
  4. a) 27.75 g
  5. d) 3.01 × 10²³
  6. a) 0.225 moles
  7. a) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
  8. a) 1⁺
  9. d) 6.022 × 10²³
  10. d) Ca₃P₂
  11. c) (g)
  12. c) 4 moles
  13. d) 6.022 × 10²³ molecules
  14. a) 111 g
  15. c) Mg₃N₂
  16. a) 180 g/mol
  17. b) 3.6 moles
  18. d) The mass of one mole of a substance
  19. c) CH
  20. d) It allows atoms and molecules to be counted through measurable amounts of matter
  21. c) 44 g/mol
  22. b) CH
  23. d) CH₂
  24. c) C₆H₆
  25. d) 58.5 g
  26. c) 56 g
  27. d) Gas
  28. a) 44 g
  29. a) 98 g/mol
  30. b) N₂H₄
  31. a) 18 g
  32. b) N₂ + 3H₂ ⇌ 2NH₃
  33. b) 273 g
  34. a) 28 g/mol
  35. b) CH
  36. b) 273 g
  37. a) Aqueous solution
  38. c) Li₂O
  39. b) 2 moles
  40. c) HO
  41. a) 58.5 g/mol
  42. b) Al₂O₃
  43. c) Water (H₂O)
  44. a) 1.505 × 10²⁴
  45. d) The law of conservation of mass
  46. d) 32 g/mol
  47. b) 2.016 g/mol
  48. d) Writing chemical formulas of ionic compounds
  49. b) 111 g
  50. b) 4Al + 3O₂ → 2Al₂O₃
  51. c) Avogadro
  52. b) (l)
  53. a) 1.008 g/mol
  54. c) CaCl₂
  55. c) ⇌
  56. b) Al₂O₃
  57. b) 6.022 × 10²³
  58. d) Reactants and products are continuously converted into one another
  59. c) Liquid
  60. c) 45 g
  61. d) 108 g
  62. b) Zinc displaces hydrogen
  63. d) (g)
  64. b) O₂, N₂, H₂
  65. c) 0.255 moles
  66. b) H₂O
  67. a) 98 g/mol
  68. c) 1.32 g
  69. d) CH₂O
  70. b) Li₂O
  71. a) 6.022 × 10²³ molecules
  72. b) C₂H₄O₂
  73. d) ⇌
  74. c) 7.2 g
  75. b) Solid
  76. b) HO
  77. b) HO
  78. b) O₃
  79. a) 7.2 g
  80. a) CH
  81. c) NaCl
  82. c) 6.022 × 10²³ amu
  83. c) 5.4 moles
  84. a) 98 g/mol
  85. d) Ions bonded in a crystal
  86. a) 1.002 × 10²³ atoms
  87. b) The number of atoms or molecules in one mole

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