Hey there, future chemists! 👋 Whether you're gearing up for MDCAT, ECAT, or FSC, this blog will help you ace the Stoichiometry unit with ease. Get ready to dive into the fundamental concepts of chemistry through carefully crafted MCQs that will prepare you for any exam! Let’s make learning fun and easy! 💡
This blog is designed to give you a perfect start to mastering Stoichiometry – one of the most important topics in the Fundamental Concepts of Chemistry for exams like MDCAT, ECAT, and FSC! 📚✨ Whether you're preparing for competitive exams or strengthening your basics, these MCQs will boost your confidence and test your knowledge!
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🌟 11. Which of the following formula represents an acid anhydride?
🌟 12. How many neutrons are contained in the nucleus of an element with Z = 27 and A = 59?
🌟 13. How many grams of NaOH are needed to make 1000g of a 5% solution?
🌟 14. nm is …………. than μm.
🌟 15. Which one is larger than dm³?
🌟 16. Which of the following is classified as a monoatomic element?
🌟 17. The decimal equivalent of 1/60 to three significant figures is:
🌟18. How many significant figures are contained in 0.00050890400?
🌟 19. One cm³ is equal to:
🌟 20. The number of protons in one molecule of HNO₃ are:
🌟 21. Which one of the following is NOT an iso electronic pair?
🟦 A. Ca²⁺, K🟩 B. Na⁺, Ne🟥 C. K⁺, Cl⁻🟨 D. O²⁻, Al³⁺
🌟 22. Which of the following formula represents a basic anhydride?
🟦 A. CO🟩 B. CrO₃🟥 C. MgO🟨 D. NO
🌟 23. The basic oxide in the given list is:
🟦 A. N₂O₅🟩 B. P₄O₆🟥 C. Sb₄O₆🟨 D. Bi₂O₃
🌟 24. If an element M forms an oxide with formula MO, which of the following is a correct formula?
🟦 A. MCl🟩 B. MS🟥 C. MCl₂🟨 D. Both B and C
🌟 25. The formula of KAl(SO₄)₂ represents a total of:
🟦 A. 6 atoms🟩 B. 7 atoms🟥 C. 12 atoms🟨 D. 14 atoms
🌟 26. The diameter of atoms is of the order of:
🟦 A. 2 × 10⁻⁵ m🟩 B. 2 × 10⁻¹⁰ m🟥 C. 2 × 10⁻² m🟨 D. 2 × 10⁻³ m
🌟 27) 51.084 g has five significant figures while 0.00510840 mg has ……….. significant figures.
🟦 A. 4🟩 B. 6🟥 C. 5🟨 D. 3
🌟 28) 1 is written in exponential notation as:
🟦 A. 10¹🟩 B. 10⁰🟥 C. 10²🟨 D. 10³
🌟 29) 67.84 g has four significant figures while 0.00678400 mg has ……….. significant figures.
🟦 A. 4🟩 B. 6🟥 C. 5🟨 D. 3
🌟30. How many significant figures are contained in 0.00020089400 mm?
🟦 A. 6🟩 B. 4🟥 C. 8🟨 D. 11
🌟 31) 75.5 g has three significant figures while 0.00755 mg has ……….. significant figures.
🟦 A. 2🟩 B. 3🟥 C. 5🟨 D. 6
🌟 32. Which one is the incorrect relation?
🟦 A. 1 m³ = 10² dm³🟩 B. 1 cm³ = 10⁻⁶ m³🟥 C. 1 cm³ = 10⁻³ dm³🟨 D. 1 dm³ = 10³ cm³
🌟 33. The digit that can be significant at times is:
🟦 A. 1🟩 B. 3🟥 C. 7🟨 D. 0
🌟 34) 8.687 has rounded off to two significant figures as:
🟦 A. 8.7🟩 B. 8.6🟥 C. 8.700🟨 D. 8.70
🌟 35. The property of measurement reflected by significant figures is:
🟦 A. Purity🟩 B. Precision🟥 C. Perfection🟨 D. All of them
🌟 36) 0.00000000000000000000000000000000091096 is expressed in exponential notation as:
🟦 A. 9.1096 × 10⁻³⁶🟩 B. 9.1096 × 10⁻³⁰🟥 C. 9.1096 × 10⁻³¹🟨 D. 9.1096 × 10⁻³²
🌟 37) 28.987 has rounded off to two significant figures as:
🟦 A. 28.9🟩 B. 28🟥 C. 29🟨 D. 29.0
🌟 38. The prefix 10¹⁸ represents:
🟦 A. Kilo🟩 B. Nano🟥 C. Exa🟨 D. Giga
🌟 39. Which one of the following is anhydride of sulphuric acid?
🟦 A. Sulphur(II) oxide🟩 B. Sulphur(III) oxide🟥 C. Sulphur(VI) oxide🟨 D. Iron pyrite
🌟 40. Which one is the incorrect relation?
🟦 A. 1 L = 10³ mL🟩 B. 1 cm³ = 10⁻⁶ m³🟥 C. 1 cm³ = 10⁻³ dm³🟨 D. 1 kg = 10² g
🌟 41. An atom has 9 protons and 10 neutrons, the atom is:
🟦 A. N🟩 B. O🟥 C. B🟨 D. F
🌟 42. Which of the following has infinite significant figures?
🟦 A. 22.40 cm🟩 B. 3.00 g🟥 C. Avogadro’s number🟨 D. 0.0045 m
🌟 43. Round off 2.3746 to 3 significant figures:
🟦 A. 2.37🟩 B. 2.38🟥 C. 2.36🟨 D. 2.374
🌟 44. The number of significant figures in 6.022 × 10²³ is:
🟦 A. 3🟩 B. 4🟥 C. 5🟨 D. Infinite
🌟 45. 4.578 has 4 significant figures. It can be changed to 7 significant figures by:
🟦 A. Placing decimal🟩 B. Placing decimal after 8 and adding 2 zeros🟥 C. Adding 3 zeros at the end🟨 D. None of them
🌟 46. 13.89 has 4 significant figures. It can be changed to 6 significant figures by:
🟦 A. Removing decimal🟩 B. Placing one zero at the end🟥 C. Simply adding two zeros at the end🟨 D. None of them
🌟 47. The similarity between 0.6850 and 6850 is that:
🟦 A. Both have 3 significant figures🟩 B. Both have 4 digits🟥 C. Both have 1 Non-significant zero🟨 D. Both have 4 significant figures
🌟 48. The lesser the number of significant figures, the:
🟦 A. Greater is the uncertainty🟩 B. Smaller is the uncertainty🟥 C. Smaller is certainty🟨 D. Both A and C
🌟 49) 3.69 has 3 significant figures. It can be changed to 6 significant figures by:
🟦 A. Placing decimal🟩 B. Placing decimal after 9 and adding 3 zeros🟥 C. Adding 3 zeros at the end🟨 D. None of them
🌟 50. Chlorine atom and chloride ions:
🟦 A. Have same number of protons🟩 B. Have same number of electrons🟥 C. Are allotropes of chlorine🟨 D. Are chemically identical
🌟 51. Which of the following statements is FALSE if the number has greater number of significant figures?
🟦 A. Greater is the precision🟩 B. Smaller is uncertainty🟥 C. Greater is the certainty🟨 D. Lesser is the precision
🌟 52. The similarity between 0.569 and 569 is that:
🟦 A. Both have 3 significant figures🟩 B. Both have 4 digits🟥 C. Both have 1 Non-significant zero🟨 D. Both have 4 significant figures
🌟 53. The greater the number of significant figures, the:
🟦 A. Greater is the uncertainty🟩 B. Smaller is the uncertainty🟥 C. Smaller is certainty🟨 D. Both A and C
🌟 54. The greater the number of significant figures, the:
🟦 A. Smaller is the uncertainty🟩 B. Greater is the precision🟥 C. Greater is the certainty🟨 D. All of them
🌟 55. Zero in decimal figure is significant if it is present:
🟦 A. On extreme right at the end🟩 B. On left side between decimal & non-zero digit when number is < 1🟥 C. Between two non-zero digits🟨 D. Both A and C are true
🌟 56. 6.55 has 3 significant figures. It can be changed to 5 significant figures by:
🟦 A. Removing decimal🟩 B. Placing two zeros at the end🟥 C. Simply adding a zero at the end🟨 D. None of them
🌟 57. Zero in decimal figure is insignificant if it is:
🟦 A. On extreme right at the end🟩 B. Between two non-zero digits🟥 C. On left side of non-zero digit while number is < 1🟨 D. None of these
🌟 58. Which figures are significant?
🟦 A. All non-zero figures🟩 B. Trailing zeros to the right of a decimal point🟥 C. Any zeros between significant figures🟨 D. All of the above
🌟 59. The correct set of significant figures is:
🟦 A. 0.00056 has 5 significant figures🟩 B. 1.2300 has 5 significant figures🟥 C. 0.100 has 1 significant figure🟨 D. 2.5 × 10³ has 4 significant figures
🌟 60. The correct set of significant figures is:
🟦 A. 0.00750 → 3 significant figures🟩 B. 2.50 × 10³ → 4 significant figures🟥 C. 1.0050 → 5 significant figures🟨 D. 200 → 3 significant figures
🌟 61. The mass of one mole of electrons is:
🟦 A. 1.008 mg🟩 B. 0.55 mg🟥 C. 0.184 mg🟨 D. 1.673 mg
🌟 62. The largest number of molecules are present in:🟦 A. 3.6 g of water
🟩 B. 4.8 g of C₂H₅OH
🟥 C. 2.8 g of CO
🟨 D. 5.4 g of N₂O₅
🌟 63. If 28 g of N₂ gas comprises of z molecules; how many molecules are there in 16 g of oxygen?
🟦 A. z🟩 B. 2 z🟥 C. ½ z🟨 D. ¼ z
🌟 64. The mass of a single hydrogen atom is:🟦 A. 1.67 × 10⁻²² g
🟩 B. 1.67 × 10⁻²⁴ kg
🟥 C. 1 g
🟨 D. 1.67 × 10⁻²⁷ kg
🌟 65. One mole of carbon-12 has a mass of:
🟦 A. 0.012 kg🟩 B. 0.0224 kg🟥 C. 12 kg🟨 D. 1 kg
🌟 66. The molar mass of formaldehyde is …………
🟦 A. 30🟩 B. 40🟥 C. 26🟨 D. None of them
🌟 67. What is the mass of one mole of iodine molecule?
🟦 A. 53 g🟩 B. 127 g🟥 C. 254 g🟨 D. 74 g
🌟 68. The volume occupied by a 0.1 mole of a gas at STP is:
🟦 A. 22400 cm³🟩 B. 2.24 dm³🟥 C. 22.4 dm³🟨 D. 5.6 dm³
🌟 69. The relative atomic mass of chlorine is 35.5 amu, the mass in grams of 0.5 moles of chlorine gas is:
🟦 A. 71 g🟩 B. 35.5 g🟥 C. 142 g🟨 D. 17.75 g
🌟 70. The total number of ions in CaCl₂ is:
🟦 A. 6.02 × 10²³🟩 B. 12.04 × 10²³🟥 C. 18.06 × 10²³🟨 D. 24.08 × 10²³
🌟 71. 1 atom of an element weighs 1.792 × 10⁻²² g. The Atomic mass of the element is:
🟦 A. 17.92🟩 B. 1.192🟥 C. 108🟨 D. 64
🌟 72. Which of the following has maximum number of atoms?
🟦 A. 18 g of H₂O🟩 B. 4.4 g of CO₂🟥 C. 16 g of O₂🟨 D. 16 g of CH₄
🌟 73. The mass of 1 atom of hydrogen is:
🟦 A. 0.5 g🟩 B. 1.6 × 10⁻²⁴ g
🟥 C. 1 g
🟨 D. 3.2 × 10⁻²⁴ g
🌟 74. The number of sulfur atoms present in 0.2 moles of S₈ molecules is:
🟦 A. 9.63 × 10²²🟩 B. 4.82 × 10²³🟥 C. 1.20 × 10²³🟨 D. 9.63 × 10²³
🌟 75. One mole of any covalent compound contains the same number of:
🟦 A. Atoms🟩 B. Molecules🟥 C. Ions🟨 D. Electrons
🌟 76. The number of atoms in 4.25 g of NH₃ is approximately:
🟦 A. 1 × 10²³🟩 B. 2 × 10²³🟥 C. 4 × 10²³🟨 D. 6 × 10²³
🌟 77. A quantity containing Avogadro’s number of particles is called:
🟦 A. Gram atom🟩 B. Gram molecule🟥 C. Mole🟨 D. Gram formula
🌟 78. The number of formula units in 11.1 g of calcium chloride is:
🟦 A. 12.04 x 10²³🟩 B. 18.06 x 10²³🟥 C. 6.02 x 10²²🟨 D. 6.02 x 10²³
🌟 79. The number of water molecules in 1 litre of water is:🟦 A. 18
🟩 B. 18 × 1000
🟥 C. Nᴀ
🟨 D. 55.55 Nᴀ
🌟 80. Mass of one mole of electrons is ……… kg
🟦 A. 1.97 × 10⁻⁶🟩 B. 54.7 × 10⁻⁸🟥 C. 54.86 × 10⁹🟨 D. 1.97 × 10⁻³¹
81. The number of molecules in 100 ml of each of O₂, NH₃, and CO₂ at STP are:
🟦 A. O₂ = NH₃ = CO₂
🟩 B. CO₂ < O₂ < NH₃
🟥 C. NH₃ < O₂ < CO₂
🟨 D. CO₂ = NH₃ < O₂
🟦 A. O₂ = NH₃ = CO₂
🟩 B. CO₂ < O₂ < NH₃
🟥 C. NH₃ < O₂ < CO₂
🟨 D. CO₂ = NH₃ < O₂
82. Which has the maximum number of atoms?
🟦 A. 24 g of C
🟩 B. 5.6 g of Fe
🟥 C. 270 g of Al
🟨 D. 1.08 g Ag
🟦 A. 24 g of C
🟩 B. 5.6 g of Fe
🟥 C. 270 g of Al
🟨 D. 1.08 g Ag
83. Two moles of hydrogen gas at STP contains how many atoms?
🟦 A. 24.08 × 10²⁴
🟩 B. 3.01 × 10²⁴
🟥 C. 24.08 × 10²³
🟨 D. 12.04 × 10⁴⁶
🟦 A. 24.08 × 10²⁴
🟩 B. 3.01 × 10²⁴
🟥 C. 24.08 × 10²³
🟨 D. 12.04 × 10⁴⁶
84. Number of O₂ molecules present in a one-litre flask at pressure 7.6 × 10⁻¹⁰ mm of Hg at 0ºC is:
🟦 A. 2.69 × 10¹⁰
🟩 B. 2.69 × 10¹¹
🟥 C. 2.69 × 10⁹
🟨 D. None of these
🟦 A. 2.69 × 10¹⁰
🟩 B. 2.69 × 10¹¹
🟥 C. 2.69 × 10⁹
🟨 D. None of these
85. 16 g of oxygen has a volume of:
🟦 A. 22.4 dm³
🟩 B. 11.2 dm³
🟥 C. 5.6 dm³
🟨 D. 22400 cm³
🟦 A. 22.4 dm³
🟩 B. 11.2 dm³
🟥 C. 5.6 dm³
🟨 D. 22400 cm³
86. 11.2 dm³ of Cl₂ gas at STP weighs:
🟦 A. 71 g
🟩 B. 17 g
🟥 C. 35.5 g
🟨 D. 37 g
🟦 A. 71 g
🟩 B. 17 g
🟥 C. 35.5 g
🟨 D. 37 g
87. Which one of the following represents the value of 1 a.m.u.?
🟦 A. 1.667 × 10⁻²⁴ g
🟩 B. 1.667 × 10⁻²³ g
🟥 C. 1.667 × 10⁻²⁷ g
🟨 D. 1.667 × 10⁻²⁸ g
🟦 A. 1.667 × 10⁻²⁴ g
🟩 B. 1.667 × 10⁻²³ g
🟥 C. 1.667 × 10⁻²⁷ g
🟨 D. 1.667 × 10⁻²⁸ g
88. This one of the following pairs has the same number of molecules:
🟦 A. 10 g H₂ & 10 g CH₄
🟩 B. 10 g H₂ & 50 g CH₄
🟥 C. 10 g H₂ & 80 g CH₄
🟨 D. 10 g H₂ & 16 g CH₄
🟦 A. 10 g H₂ & 10 g CH₄
🟩 B. 10 g H₂ & 50 g CH₄
🟥 C. 10 g H₂ & 80 g CH₄
🟨 D. 10 g H₂ & 16 g CH₄
89. One cm³ of oxygen gas at STP contains about:
🟦 A. 1 × 10²⁰ atoms
🟩 B. 6 × 10²³ atoms
🟥 C. 1.67 × 10²⁴ atoms
🟨 D. 0.53 × 10²⁰ atoms
🟦 A. 1 × 10²⁰ atoms
🟩 B. 6 × 10²³ atoms
🟥 C. 1.67 × 10²⁴ atoms
🟨 D. 0.53 × 10²⁰ atoms
90. The number of atoms in 558.5 grams of Fe (atomic weight of Fe = 55.85 g/mol) is:
🟦 A. Twice that in 60 g of carbon
🟩 B. 558.5 × 6.023 × 10²³
🟥 C. Half that in 8 g of He
🟨 D. 6.023 × 10²²
🟦 A. Twice that in 60 g of carbon
🟩 B. 558.5 × 6.023 × 10²³
🟥 C. Half that in 8 g of He
🟨 D. 6.023 × 10²²
91. Calculate the number of moles in 1 m³ of gas at STP:
🟦 A. 4.46
🟩 B. 44.6
🟥 C. 446
🟨 D. 4460
🟦 A. 4.46
🟩 B. 44.6
🟥 C. 446
🟨 D. 4460
92. Which of the following will contain the same number of atoms as 20 g of calcium?
🟦 A. 12 g magnesium
🟩 B. 12 g carbon
🟥 C. 16 g oxygen atom
🟨 D. 8 g oxygen gas
🟦 A. 12 g magnesium
🟩 B. 12 g carbon
🟥 C. 16 g oxygen atom
🟨 D. 8 g oxygen gas
93. One mole of P₄ molecules contains:
🟦 A. 1 molecule
🟩 B. 24.088 × 10²³ atoms
🟥 C. ¼ × 6.022 × 10²³ atoms
🟨 D. 4 molecules
🟦 A. 1 molecule
🟩 B. 24.088 × 10²³ atoms
🟥 C. ¼ × 6.022 × 10²³ atoms
🟨 D. 4 molecules
94. In which of the following pairs do 1 g of each have an equal number of molecules?
🟦 A. N₂O and CO
🟩 B. N₂ and C₃O₂
🟥 C. N₂ and CO
🟨 D. N₂O and CO₂
🟦 A. N₂O and CO
🟩 B. N₂ and C₃O₂
🟥 C. N₂ and CO
🟨 D. N₂O and CO₂
95. 400 g of caustic soda constitutes its … gram formula:
🟦 A. 1
🟩 B. 5
🟥 C. 10
🟨 D. Half
🟦 A. 1
🟩 B. 5
🟥 C. 10
🟨 D. Half
96. The mass of 1 atom of diamond is:
🟦 A. 2.99 × 10⁻²³ g
🟩 B. 1.99 × 10⁻²³ g
🟥 C. 3.99 × 10⁻²³ g
🟨 D. 2.99 × 10⁻²⁴ g
🟦 A. 2.99 × 10⁻²³ g
🟩 B. 1.99 × 10⁻²³ g
🟥 C. 3.99 × 10⁻²³ g
🟨 D. 2.99 × 10⁻²⁴ g
97. The mass of 1 dm³ of nitrogen gas at STP is:
🟦 A. 1.25
🟩 B. 1.43
🟥 C. 0.089
🟨 D. None of them
🟦 A. 1.25
🟩 B. 1.43
🟥 C. 0.089
🟨 D. None of them
98) 11200 ml of argon gas at STP weighs:
🟦 A. 40
🟩 B. 20
🟥 C. 30
🟨 D. 10
🟦 A. 40
🟩 B. 20
🟥 C. 30
🟨 D. 10
99) 840 g of baking soda constitutes its … gram formula:
🟦 A. 5
🟩 B. Half
🟥 C. 10
🟨 D. 2
🟦 A. 5
🟩 B. Half
🟥 C. 10
🟨 D. 2
100. The mass of 1 atom of uranium is:
🟦 A. 3.95 × 10⁻²³ g
🟩 B. 3.95 × 10⁻²⁴ g
🟥 C. 3.95 × 10⁻²² g
🟨 D. None of them
🟦 A. 3.95 × 10⁻²³ g
🟩 B. 3.95 × 10⁻²⁴ g
🟥 C. 3.95 × 10⁻²² g
🟨 D. None of them
📝 Answer Key:
🟥 C. 12.04 x 10²³
🟦 A. 11.2 dm³
🟨 D. 72 x 10²³
🟦 A. 16g S
🟩 B. 3.01 × 10²⁴
🟩 B. 100g CH₄
🟩 B. The mass of 1 mole of Cl₂ gas is 35.5g
🟥 C. Its value changes if temperature increases
🟩 B. Less than theoretical yield
🟦 A. 1 dm³ of methane gas at STP
🟨 D. SO₃
🟩 B. 32
🟨 D. 50g
🟩 B. Less
🟥 C. m³
🟨 D. Helium
🟩 B. 0.0167
🟥 C. 8
🟦 A. 10⁻³ dm³
🟨 D. 32
🟦 A. Ca²⁺, K
-
🟥 C. MgO
-
🟨 D. Bi₂O₃
-
🟨 D. Both B and C
-
🟥 C. 12 atoms
-
🟩 B. 2 × 10⁻¹⁰ m
-
🟥 B. B
-
🟩 B. 10⁰
-
🟩 B. 6
-
🟥 C. 8
🟥 C. 5
-
🟦 A. 1 m³ = 10² dm³
-
🟨 D. 0
-
🟦 A. 8.7
-
🟩 B. Precision
-
🟥 C. 9.1096 × 10⁻³¹
-
🟥 C. 29
-
🟩 C. Exa
-
🟥 C. Sulphur(VI) oxide
-
🟨 D. 1 kg = 10² g
🟨 D. F
-
🟥 C. Avogadro’s number
-
🟩 B. 2.38
-
🟩 B. 4
-
🟥 C. Adding 3 zeros at the end
-
🟥 C. Simply adding two zeros at the end
-
🟩 B. Both have 4 digits
-
🟨 D. Both A and C
-
🟥 C. Adding 3 zeros at the end
-
🟦 A. Have same number of protons
🟨 D. Lesser is the precision
-
🟦 A. Both have 3 significant figures
-
🟩 B. Smaller is the uncertainty
-
🟨 D. All of them
-
🟨 D. Both A and C are true
-
🟩 B. Placing two zeros at the end
-
🟥 C. On left side of non-zero digit while number is < 1
-
🟨 D. All of the above
-
🟩 B. 1.2300 has 5 significant figures
-
🟥 C. 1.0050 → 5 significant figures
🟩 B. 0.55 mg
-
🟦 A. 3.6 g of water
-
🟥 C. ½ z
-
🟨 D. 1.67 × 10⁻²⁷ kg
-
🟦 A. 0.012 kg
-
🟦 A. 30
-
🟥 C. 254 g
-
🟩 B. 2.24 dm³
-
🟩 B. 35.5 g
-
🟥 C. 18.06 × 10²³
🟥 C. 108
-
🟨 D. 16 g of CH₄
-
🟩 B. 1.6 × 10⁻²⁴ g
-
🟨 D. 9.63 × 10²³
-
🟩 B. Molecules
-
🟨 D. 6 × 10²³
-
🟩 C. Mole
-
🟥 C. 6.02 x 10²²
-
🟨 D. 55.55 Nᴀ
-
🟦 A. 1.97 × 10⁻⁶
🟦 A. O₂ = NH₃ = CO₂
🟩 C. 270 g of Al
🟩 C. 24.08 × 10²³
🟩 B. 2.69 × 10¹¹
🟩 B. 11.2 dm³
🟥 C. 35.5 g
🟦 A. 1.667 × 10⁻²⁴ g
🟥 C. 10 g H₂ & 80 g CH₄
🟨 D. 0.53 × 10²⁰ atoms
🟦 A. Twice that in 60 g of carbon
🟩 B. 44.6
🟦 A. 12 g magnesium
🟩 B. 24.088 × 10²³ atoms
🟩 C. N₂ and CO
🟥 C. 10
🟩 B. 1.99 × 10⁻²³ g
🟦 A. 1.25
🟩 B. 20
🟥 C. 10
🟥 C. 3.95 × 10⁻²² g
📝 Explanations:
1. 🟥 C. 12.04 x 10²³
Explanation:
No. of molecules = Vᶃ/Vᴍ × Nᴀ
2.🟦 A. 11.2 dm³
Explanation:
3. 🟨 D. 72 x 10²³
Explanation:
1 mole of sugar contains 12 moles of carbon.
No. of carbon atoms = 12 × Nᴀ = 72 × 10²³
4. 🟦 A. 16g S
Explanation:
81. 🟦 A. O₂ = NH₃ = CO₂
Explanation:
82. 🟩 C. 270 g of Al
Explanation:
To find the largest number of atoms, we need to calculate the number of moles for each substance:
5.6 g of Fe = 0.1 mole
270 g of Al = 10 moles
1.08 g of Ag = 0.01 mole
Therefore, Al has the greatest number of atoms.
83. 🟩 C. 24.08 × 10²³
Explanation:
For 2 moles of hydrogen gas (H₂), the number of atoms = atomicity × moles × Avogadro’s number = 2 × 2 × = 24.08 × 10²³ atoms.
84. 🟩 B. 2.69 × 10¹¹
Explanation:
Use the ideal gas law to calculate the number of molecules in 1L of oxygen gas at the given pressure and temperature, yielding approximately 2.69 × 10¹¹ molecules.
85. 🟩 B. 11.2 dm³
Explanation:
At STP, 32 g of O₂ equals 22.4 dm³. Therefore, 16 g of O₂ = 11.2 dm³.
86. 🟥 C. 35.5 g
Explanation:
At STP, 22.4 dm³ of Cl₂ weighs 71 g. Therefore, 11.2 dm³ weighs 35.5 g.
87. 🟦 A. 1.667 × 10⁻²⁴ g
Explanation:
1 atomic mass unit (amu) is defined as 1.667 × 10⁻²⁴ g, which is the mass of one hydrogen atom.
88. 🟥 C. 10 g H₂ & 80 g CH₄
Explanation:
For equal moles (5 moles), you will have the same number of molecules:
10 g H₂ = 5 mol
80 g CH₄ = 5 mol
Thus, they contain the same number of molecules.
89. 🟨 D. 0.53 × 10²⁰ atoms
Explanation:
At STP, one cm³ of oxygen gas contains approximately 0.53 × 10²⁰ atoms. This is derived from the molar volume of gases at STP and the atomicity of O₂.
90. 🟦 A. Twice that in 60 g of carbon
Explanation:
The number of atoms in 558.5 g of Fe = ²³
This gives twice the number of atoms as in 60 g of carbon (which is 1 mole of carbon, or
91. 🟩 B. 44.6
Explanation:
1 m³ = 1000 L
At STP, 22.4 L = 1 mole, so:
1000 L =
92. 🟦 A. 12 g magnesium
Explanation:
20 g of calcium = 0.5 moles (since atomic mass of calcium = 40).
12 g of magnesium (atomic mass 24) also constitutes 0.5 moles.
Thus, both contain the same number of atoms.
93. 🟩 B. 24.088 × 10²³ atoms
Explanation:
1 mole of P₄ molecules contains 6.022 × 10²³ molecules.
94. 🟩 C. N₂ and CO
Explanation:
For 1 g of each to have the same number of molecules, their molar masses must be the same.
The molar mass of N₂ (28 g/mol) is the same as CO (28 g/mol), so 1 g of each will contain the same number of molecules.
95. 🟥 C. 10
Explanation:
1 mole (or gram formula) of NaOH (caustic soda) weighs 40 g.
Therefore, 400 g of NaOH contains 10 moles, i.e., 10 gram formulas.
96. 🟩 B. 1.99 × 10⁻²³ g
Explanation:
Mass of 1 atom of diamond = ⁻²³
97. 🟦 A. 1.25
Explanation:
For 1 dm³ of nitrogen gas at STP, the molar volume is 22.4 L (or 0.0224 m³).
Thus, the mass = = 1.25 g.
98. 🟩 B. 20
Explanation:
At STP, molar volume of argon = 22.4 L (22400 mL).
Thus, 11200 mL = half the molar volume, which is 20 g.
99. 🟥 C. 10
Explanation:
1 mole of baking soda (NaHCO₃) weighs 84 g.
Thus, 840 g = 10 moles or 10 gram formulas.
100. 🟥 C. 3.95 × 10⁻²² g
Explanation:
Mass of 1 atom of uranium =
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