1. For the reaction 2H₂ + O₂ → 2H₂O, how many moles of H₂O are produced from 4.0 moles of O₂ (assuming excess H₂)?
- (A) 2.0 moles
- (B) 4.0 moles
- (C) 6.0 moles
- (D) 8.0 moles
View Answer
Correct Answer: (D) 8.0 moles
Explanation: From the balanced equation, 1 mole O₂ produces 2 moles H₂O.
Moles H₂O = 4.0 moles O₂ × (2 moles H₂O / 1 mole O₂) = 8.0 moles2. For N₂ + 3H₂ → 2NH₃, if 0.50 moles of N₂ react with excess H₂, how many grams of NH₃ are produced?
- (A) 8.5 g
- (B) 17.0 g
- (C) 25.5 g
- (D) 34.0 g
View Answer
Correct Answer: (B) 17.0 g
Explanation: Molar mass NH₃ = 17 g/mol.
Moles NH₃ = 0.50 moles N₂ × (2 moles NH₃ / 1 mole N₂) = 1.0 mole
Mass NH₃ = 1.0 mol × 17 g/mol = 17.0 g3. For CH₄ + 2O₂ → CO₂ + 2H₂O, if 16.0 g of CH₄ is combusted, what mass of CO₂ is produced?
- (A) 11.0 g
- (B) 22.0 g
- (C) 44.0 g
- (D) 88.0 g
View Answer
Correct Answer: (C) 44.0 g
Explanation: Molar mass CH₄ = 16 g/mol, CO₂ = 44 g/mol.
Moles CH₄ = 16.0 g / 16 g/mol = 1.0 mol
Moles CO₂ = 1.0 mol (1:1 ratio)
Mass CO₂ = 1.0 mol × 44 g/mol = 44.0 g4. For 2H₂ + O₂ → 2H₂O, with 5.0 moles H₂ and 2.0 moles O₂, what is the limiting reagent?
- (A) H₂
- (B) O₂
- (C) Neither (stoichiometric)
- (D) Both equally
View Answer
Correct Answer: (B) O₂
Explanation: O₂ required for 5.0 mol H₂ = 2.5 mol, but only 2.0 mol available → O₂ limiting5. For 2Na + Cl₂ → 2NaCl, with 23.0 g Na and 10.0 g Cl₂, what mass of NaCl is produced?
- (A) 16.4 g
- (B) 32.8 g
- (C) 49.2 g
- (D) 58.5 g
View Answer
Correct Answer: (A) 16.4 g
Explanation: Moles Cl₂ = 10.0/71 ≈ 0.14 mol
Moles NaCl = 0.14 × 2 = 0.28 mol
Mass NaCl = 0.28 × 58.5 ≈ 16.4 g6. For 2H₂ + O₂ → 2H₂O, with 10.0 g H₂ and 40.0 g O₂, what mass of excess reactant remains?
- (A) 5.0 g H₂
- (B) 10.0 g H₂
- (C) 20.0 g O₂
- (D) 35.0 g O₂
View Answer
Correct Answer: (A) 5.0 g H₂
Explanation: H₂ used = 5.0 g (from 40 g O₂)
H₂ remaining = 10.0 g - 5.0 g = 5.0 g7. For CaCO₃ → CaO + CO₂, what mass of CaCO₃ is needed to produce 5.00 g CaO?
- (A) 5.00 g
- (B) 8.93 g
- (C) 10.00 g
- (D) 17.86 g
View Answer
Correct Answer: (B) 8.93 g
Explanation: Moles CaO = 5.00/56 ≈ 0.0893 mol
Mass CaCO₃ = 0.0893 × 100 = 8.93 g8. For 2Al + 3Cl₂ → 2AlCl₃, with 4.0 moles Al and 6.0 moles Cl₂, how many moles of AlCl₃ are produced?
- (A) 2.0 moles
- (B) 4.0 moles
- (C) 6.0 moles
- (D) 8.0 moles
View Answer
<极code>Correct Answer: (B) 4.0 moles Explanation: Perfect stoichiometric ratio (2Al:3Cl₂) Moles AlCl₃ = 4.0 mol Al × (2 mol AlCl₃/2 mol Al) = 4.0 mol
9. Why must chemical equations be balanced before stoichiometric calculations?
- (A) To determine reaction speed
- (B) To obey Law of Conservation of Mass
- (C) To calculate reaction energy
- (D) To identify physical states
View Answer
Correct Answer: (B) To obey Law of Conservation of Mass
Explanation: Balancing ensures atoms/mass are conserved and provides correct mole ratios10. What is a limiting reactant?
- (A) The reactant with largest mass
- (B) The reactant completely consumed first
- (C) The catalyst for the reaction
- (D) The product of the reaction
View Answer
Correct Answer: (B) The reactant completely consumed first
Explanation: It limits product formation as reaction stops when it's depleted11. What volume will 2.00 moles of ideal gas occupy at STP?
- (A) 11.2 L
- (B) 22.4 L
- (C) 44.8 L
- (D) 89.6 L
View Answer
Correct Answer: (C) 44.8 L
Explanation: At STP, 1 mole = 22.4 L → 2.00 × 22.4 = 44.8 L12. A gas occupies 11.2 L at STP. How many moles are present?
- (A) 0.25 mol
- (B) 0.50 mol
- (C) 1.00 mol
- (D) 2.00 mol
View Answer
Correct Answer: (B) 0.50 mol
Explanation: Moles = 11.2 L / 22.4 L/mol = 0.500 mol13. Zn + 2HCl → ZnCl₂ + H₂. What volume of H₂ (STP) is produced from 5.00 g Zn?
- (A) 0.86 L
- (B) 1.72 L
- (C) 3.44 L
- (D) 6.88 L
View Answer
Correct Answer: (B) 1.72 L
Explanation: Moles Zn = 5.00/65 ≈ 0.0769 mol
Volume H₂ = 0.0769 × 22.4 ≈ 1.72 L14. CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. What mass of CaCO₃ is needed for 10.0 L CO₂ at STP?
- (A) 22.3 g
- (B) 44.6 g
- (C) 66.9 g
- (D) 89.2 g
View Answer
Correct Answer: (B) 44.6 g
Explanation: Moles CO₂ = 10.0/22.4 ≈ 0.446 mol
Mass CaCO₃ = 0.446 × 100 = 44.6 g15. 2H₂ + O₂ → 2H₂O. If 10.0 L H₂ reacts at STP, what volume of H₂O vapor is produced at STP?
- (A) 5.0 L
- (B) 10.0 L
- (C) 20.0 L
- (D) 40.0 L
View Answer
Correct Answer: (B) 10.0 L
Explanation: 2 volumes H₂ produce 2 volumes H₂O → same volume16. What are standard STP conditions?
- (A) 0°C and 1 atm
- (B) 25°C and 1 atm
- (C) 0°C and 760 torr
- (D) Both (A) and (C)
View Answer
Correct Answer: (D) Both (A) and (C)
Explanation: STP = 0°C (273 K) and 1 atm (760 torr)17. Theoretical yield = 20.0 g, actual yield = 15.0 g. What is percent yield?
- (A) 65.0%
- (B) 70.0%
- (C) 75.0%
- (D) 133%
View Answer
Correct Answer: (C) 75.0%
Explanation: (15.0/20.0) × 100% = 75.0%18. Theoretical yield = 40.0 g, percent yield = 80%. What is actual yield?
- (A) 32.0 g
- (B) 40.0 g
- (C) 48.0 g
- (D) 50.0 g
View Answer
Correct Answer: (A) 32.0 g
Explanation: 40.0 g × 0.80 = 32.0 g19. Accepted value = 5.00 g, experimental yield = 4.70 g. What is percent error?
- (A) 4.0%
- (B) 6.0%
- (C) 6.4%
- (D) 10.0%
View Answer
Correct Answer: (B) 6.0%
Explanation: |4.70-5.00|/5.00 × 100% = 6.00%20. What distinguishes percent yield from percent error?
- (A) Yield measures efficiency; error measures accuracy
- (B) Yield uses theoretical value; error uses experimental
- (C) Yield applies to products; error applies to measurements
- (D) All of the above
View Answer
Correct Answer: (D) All of the above
Explanation: Percent yield = (actual/theoretical)×100%; Percent error = |exp - accepted|/accepted ×100%21. Why might percent yield exceed 100%?
- (A) Incomplete product purification
- (B) Presence of impurities
- (C) Measurement errors
- (D) All of the above
View Answer
Correct Answer: (D) All of the above
Explanation: Impurities, unreacted reactants, or incomplete drying can increase mass22. What best defines theoretical yield?
- (A) Maximum possible product
- (B) Actual lab-obtained product
- (C) Yield from side reactions
- (D) Minimum expected product
View Answer
Correct Answer: (A) Maximum possible product
Explanation: Theoretical yield is calculated from stoichiometry under ideal conditions23. Element X: X-10 (10.0 amu, 20%), X-11 (11.0 amu, 80%). Average atomic mass?
- (A) 10.0 amu
- (B) 10.5 amu
- (C) 10.8 amu
- (D) 11.0 amu
View Answer
Correct Answer: (C) 10.8 amu
Explanation: (10.0×0.20) + (11.0×0.80) = 2.0 + 8.8 = 10.8 amu24. Element Z: Z-63 abundance = 70%, average mass = 63.6 amu. Abundance of Z-65?
- (A) 20%
- (B) 30%
- (C) 40%
- (D) 50%
View Answer
Correct Answer: (B) 30%
Explanation: (63×0.70) + 65x = 63.6 → 44.1 + 65x = 63.6 → x = 0.3025. Chlorine atomic mass = 35.45 amu. Which isotope is more abundant?
- (A) Cl-35
- (B) Cl-37
- (C) Both equally
- (D) Cannot determine
View Answer
Correct Answer: (A) Cl-35
Explanation: 35.45 is closer to 35 than 37, so Cl-35 is more abundant26. Why is atomic mass not a whole number?
- (A) Weighted average of isotopes
- (B) Measurement errors
- (C) Quantum effects
- (D) Nuclear binding energy
View Answer
Correct Answer: (A) Weighted average of isotopes
Explanation: Atomic mass accounts for all natural isotopes and their abundances27. Which compound is soluble in water?
- (A) AgCl
- (B) PbSO₄
- (C) KNO₃
- (D) CaCO₃
View Answer
Correct Answer: (C) KNO₃
Explanation: All nitrates (NO₃⁻) are soluble28. Mixing K₂SO₄ and BaCl₂ produces which precipitate?
- (A) KCl
- (B) BaSO₄
- (C) K₂Cl₂
- (D) SO₄Cl
View Answer
Correct Answer: (B) BaSO₄
Explanation: Ba²⁺ and SO₄²⁻ form insoluble BaSO₄29. Mixing NaNO₃ and KCl produces precipitate?
- (A) Yes, NaCl
- (B) Yes, KNO₃
- (C) Yes, NaK
- (D) No precipitate
View Answer
Correct Answer: (D) No precipitate
Explanation: All possible products are soluble30. Which chloride is insoluble?
- (A) NaCl
- (B) NH₄Cl
- (C) MgCl₂
- (D) AgCl
View Answer
Correct Answer: (D) AgCl
Explanation: Ag⁺ forms insoluble chlorides (except with NH₄⁺ and group 1)31. What precipitate forms when CaCl₂(aq) + K₃PO₄(aq) react?
- (A) CaCl₂
- (B) K₃PO₄
- (C) KCl
- (D) Ca₃(PO₄)₂
View Answer
Correct Answer: (D) Ca₃(PO₄)₂
Explanation: Calcium phosphate is insoluble32. Which ion always forms soluble compounds?
- (A) Ag⁺
- (B) Pb²⁺
- (C) NO₃⁻
- (D) SO₄²⁻
View Answer
Correct Answer: (C) NO₃⁻
Explanation: All nitrates are soluble without exceptions33. Net ionic equation for Pb(NO₃)₂(aq) + KI(aq) → ?
- (A) Pb²⁺ + 2I⁻ → PbI₂(s)
- (B) K⁺ + NO₃⁻ → KNO₃(s)
- (C) Pb²⁺ + I₂ → PbI₂(s)
- (D) NO₃⁻ + K⁺ → KNO₃(s)
View Answer
Correct Answer: (A) Pb²⁺ + 2I⁻ → PbI₂(s)
Explanation: Only ions forming precipitate are shown34. Net ionic equation for HCl(aq) + NaOH(aq) → ?
- (A) H⁺ + OH⁻ → H₂O(l)
- (B) Cl⁻ + Na⁺ → NaCl(s)
- (C) H₂ + Cl₂ → 2HCl(g)
- (D) Na⁺ + Cl⁻ → NaCl(aq)
View Answer
Correct Answer: (A) H⁺ + OH⁻ → H₂O(l)
Explanation: Acid-base neutralization core reaction35. In Na₂SO₄ + BaCl₂ → BaSO₄(s), what are spectator ions?
- (A) Ba²⁺ and SO₄²⁻
- (B) Na⁺ and Cl⁻
- (C) Na⁺ and SO₄²⁻
- (D) Ba²⁺ and Cl⁻
View Answer
Correct Answer: (B) Na⁺ and Cl⁻
Explanation: Ions not involved in precipitate formation36. In H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O, what are spectator ions?
- (A) H⁺ and OH⁻
- (B) Na⁺ and SO₄²⁻
- (C) H⁺ and SO₄²⁻
- (D) Na⁺ and OH⁻
View Answer
Correct Answer: (B) Na⁺ and SO₄²⁻
Explanation: Ions not involved in water formation37. Why omit spectator ions in net ionic equations?
- (A) Simplify to essential chemical change
- (B) Hide reaction details
- (C) Reduce equation complexity
- (D) Both (A) and (C)
View Answer
Correct Answer: (D) Both (A) and (C)
Explanation: Focuses on actual chemical change and simplifies representation38. Which are strong acids?
- (A) H₂SO₄ and HCl
- (B) H₃PO₄ and HF
- (C) CH₃COOH and H₂CO₃
- (D) All acids are strong
View Answer
Correct Answer: (A) H₂SO₄ and HCl
Explanation: Strong acids fully dissociate: HCl, H₂SO₄ (first proton)39. Which are strong bases?
- (A) LiOH and Ba(OH)₂
- (B) NH₃ and Fe(OH)₃
- (C) Al(OH)₃ and Cu(OH)₂
- (D) All hydroxides
View Answer
Correct Answer: (A) LiOH and Ba(OH)₂
Explanation: Strong bases: Group 1 hydroxides and heavy group 2 hydroxides40. True about strong acids?
- (A) Same as concentrated acids
- (B) Fully dissociate in water
- (C) Have high pH values
- (D) Always liquid at room temperature
View Answer
Correct Answer: (B) Fully dissociate in water
Explanation: "Strong" refers to complete dissociation, not concentration41. Products of strong acid + strong base?
- (A) Salt + water
- (B) Acid anhydride
- (C) Basic oxide
- (D) Hydrogen gas
View Answer
Correct Answer: (A) Salt + water
Explanation: General reaction: HA + BOH → BA + H₂O42. Oxidation state of nitrogen in NO₃⁻?
- (A) +3
- (B) +5
- (C) -3
- (D) +1
View Answer
Correct Answer: (B) +5
Explanation: x + 3(-2) = -1 → x - 6 = -1 → x = +543. Oxidation state of manganese in MnO₄⁻?
- (A) +2
- (B) +4
- (C) +7
- (D) +3
View Answer
Correct Answer: (C) +7
Explanation: x + 4(-2) = -1 → x - 8 = -1 → x = +744. In Zn + CuSO₄ → ZnSO₄ + Cu, what is oxidized?
- (A) Zn
- (B) Cu²⁺
- (C) SO₄²⁻
- (D) None
View Answer
Correct Answer: (A) Zn
Explanation: Zn loses electrons (0 → +2)45. In Zn + CuSO₄ → ZnSO₄ + Cu, what is the oxidizing agent?
- (A) Zn
- (B) Cu²⁺
- (C) SO₄²⁻
- (D) Zn²⁺
View Answer
Correct Answer: (B) Cu²⁺
Explanation: Cu²⁺ causes oxidation of Zn (reduced itself)46. True about oxidizing agents?
- (A) Get oxidized
- (B) Get reduced
- (C) Always metals
- (D) Increase in oxidation state
View Answer
Correct Answer: (B) Get reduced
Explanation: Oxidizing agents accept electrons (reduced)47. Oxidation involves:
- (A) Gain of electrons
- (B) Loss of electrons
- (C) Gain of protons
- (D) Loss of neutrons
View Answer
Correct Answer: (B) Loss of electrons
Explanation: Oxidation: loss of electrons; Reduction: gain of electrons48. Balanced equation for Fe²⁺ + MnO₄⁻ → Fe³⁺ + Mn²⁺ in acid?
- (A) Fe²⁺ + MnO₄⁻ → Fe³⁺ + Mn²⁺
- (B) 5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O
- (C) 3Fe²⁺ + MnO₄⁻ + 4H⁺ → 3Fe³⁺ + Mn²⁺ + 2H₂O
- (D) Fe²⁺ + MnO₄⁻ + 4H⁺ → Fe³⁺ + Mn²⁺ + 2H₂O
View Answer
Correct Answer: (B) 5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5极³⁺ + Mn²⁺ + 4H₂O
Explanation: Standard balancing for permanganate reduction49. Balanced equation for Cr₂O₇²⁻ + Cl⁻ → Cr³⁺ + Cl₂ in acid?
- (A) Cr₂O₇²⁻ + 6Cl⁻ + 14H⁺ → 2Cr³⁺ + 3Cl₂ + 7H₂O
- (B) Cr₂O₇²⁻ + 2Cl⁻ + 8H⁺ → 2Cr³⁺ + Cl₂ + 4H₂O
- (C) Cr₂O₇²⁻ + 4Cl⁻ + 10H⁺ → 2Cr³⁺ + 2Cl₂ + 5H₂O
- (D) Cr₂O₇²⁻ + Cl⁻ + 7H⁺ → 2Cr³⁺ + Cl₂ + 7H₂O
View Answer
Correct Answer: (A) Cr₂O₇²⁻ + 6Cl⁻ + 14H⁺ → 2Cr³⁺ + 3Cl₂ + 7H₂O
Explanation: Correct stoichiometry for dichromate reduction50. Balanced equation for Cu + NO₃⁻ → Cu²⁺ + NO in acid?
- (A) Cu + NO₃⁻ + 4H⁺ → Cu²⁺ + NO + 2H₂O
- (B) 3Cu + 2NO₃⁻ + 8H⁺ → 3Cu²⁺ + 2NO + 4H₂O
- (C) Cu + NO₃⁻ + 2H⁺ → Cu²⁺ + NO + H₂O
- (D) 2Cu + NO₃⁻ + 6H⁺ → 2Cu²⁺ + NO + 3H₂O
View Answer
Correct Answer: (B) 3Cu + 2NO₃⁻ + 8H⁺ → 3Cu²⁺ + 2NO + 4H₂O
Explanation: Balanced equation with proper electron transfer