IB Chemistry (SL and HL) Examination Exam
Question 1. Which of the following is an example of a mixture?
A) Pure sodium chloride
B) Distilled water
C) Air
D) Carbon dioxide
Answer: C
Explanation: Air is a mixture because it contains several different gases (mainly nitrogen, oxygen,
argon, carbon dioxide) that are not chemically bonded.
Question 2. What is the correct chemical formula for magnesium chloride?
A) MgCl
B) MgCl₂
C) Mg₂Cl
D) Mg₂Cl₂
Answer: B
Explanation: Magnesium forms a 2+ ion and chloride is 1-. Two chloride ions are needed to balance
one magnesium ion, giving MgCl₂.
Question 3. Which term best describes a substance consisting of two or more elements chemically
combined in fixed proportions?
A) Mixture
B) Compound
C) Solution
D) Alloy
Answer: B
Explanation: A compound is formed when two or more elements are chemically combined in a fixed
ratio.
Question 4. Which statement about the atoms in a chemical reaction is correct?
A) Atoms are destroyed.
B) Atoms are created.
C) Atoms are rearranged.
D) Atoms change into energy.
Answer: C
Explanation: In a chemical reaction, atoms are rearranged to form new substances, but are neither
created nor destroyed.
Question 5. What is Avogadro’s constant?
A) 1.008
B) 6.02 × 10²³ mol⁻¹
C) 3.14
D) 9.8 m/s²
Answer: B
, IB Chemistry (SL and HL) Examination Exam
Explanation: Avogadro’s constant is the number of particles (atoms, molecules, ions) in one mole,
which is 6.02 × 10²³.
Question 6. What is the molar mass of H₂SO₄ (sulfuric acid)?
A) 34 g/mol
B) 98 g/mol
C) 100 g/mol
D) 49 g/mol
Answer: B
Explanation: H₂SO₄ has a molar mass of (2×1) + 32 + (4×16) = 2 + 32 + 64 = 98 g/mol.
Question 7. Which of the following is the correct definition of relative atomic mass?
A) The mass of one atom in grams
B) The weighted average mass of an atom compared to 1/12 of a carbon-12 atom
C) The mass number of an atom
D) The number of neutrons in an atom
Answer: B
Explanation: Relative atomic mass is a weighted average compared to 1/12 of a carbon-12 atom.
Question 8. How many moles of oxygen atoms are there in 18 g of water (H₂O)?
A) 1
B) 2
C) 0.5
D) 3
Answer: A
Explanation: Moles of H₂O = 18/18 = 1 mol; 1 mol of H₂O contains 1 mol of O atoms.
Question 9. Which calculation would you use to find the number of particles in a 0.5 mol sample?
A) 0.5 × 6.02 × 10²³
B) 0.5 ÷ 6.02 × 10²³
C) 0.5 × 1.01
D) 0.5 ÷ 1.01
Answer: A
Explanation: Number of particles = moles × Avogadro’s constant.
Question 10. What is the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and
53.3% oxygen by mass?
A) CHO
B) CH₂O
C) C₂H₂O₂
D) C₂H₄O₂
Answer: B
, IB Chemistry (SL and HL) Examination Exam
Explanation: Divide by molar masses: C: 40/12=3.33, H: 6.7/1=6.7, O: 53.3/16=3.33. Simplest ratio is
1:2:1 (CH₂O).
Question 11. In the reaction: 2Na + Cl₂ → 2NaCl, what is the limiting reactant if 4 mol Na reacts with
2 mol Cl₂?
A) Sodium
B) Chlorine
C) Sodium chloride
D) Neither
Answer: B
Explanation: 4 mol Na requires 2 mol Cl₂ (1:1 ratio), so both are used up; neither is in excess, but Cl₂
is limiting if less is present.
Question 12. If 1.6 g of oxygen gas (O₂) reacts, how many moles of O₂ are present? (Molar mass of
O₂ = 32 g/mol)
A) 0.05
B) 0.5
C) 0.2
D) 0.04
Answer: C
Explanation: Moles = mass/molar mass = 1.6/32 = 0.05 mol.
Question 13. What is the theoretical yield of NaCl when 2.3 g of Na reacts with excess Cl₂? (Na = 23,
NaCl = 58.5)
A) 5.85 g
B) 2.3 g
C) 1.15 g
D) 5.0 g
Answer: A
Explanation: 2.3 g Na = 0.1 mol; 0.1 mol NaCl = 0.1 × 58.5 = 5.85 g.
Question 14. If the actual yield of a reaction is 4.8 g and the theoretical yield is 6.0 g, what is the
percentage yield?
A) 80%
B) 60%
C) 120%
D) 20%
Answer: A
Explanation: % yield = (actual/theoretical) × 100 = (4.8/6.0) × 100 = 80%.
Question 15. What is the concentration of a solution containing 0.5 mol NaCl in 250 cm³ of water?
A) 2 mol/dm³
, IB Chemistry (SL and HL) Examination Exam
B) 0.5 mol/dm³
C) 0.2 mol/dm³
D) 1 mol/dm³
Answer: A
Explanation: 250 cm³ = 0.25 dm³; concentration = moles/volume = 0.5/0.25 = 2 mol/dm³.
Question 16. Which equation represents the ideal gas law?
A) P = nRT/V
B) PV = nRT
C) PV = RT/n
D) V = nRT/P
Answer: B
Explanation: The ideal gas law is PV = nRT.
Question 17. What is the volume at STP (273 K, 1 atm) occupied by 2 moles of an ideal gas?
A) 11.2 L
B) 22.4 L
C) 44.8 L
D) 33.6 L
Answer: C
Explanation: 1 mol gas at STP = 22.4 L; 2 mol = 44.8 L.
Question 18. What is the mass number of an atom with 12 protons and 13 neutrons?
A) 12
B) 13
C) 25
D) 1
Answer: C
Explanation: Mass number = protons + neutrons = 12 + 13 = 25.
Question 19. Which subatomic particle determines the identity (element) of an atom?
A) Neutron
B) Proton
C) Electron
D) Nucleus
Answer: B
Explanation: The number of protons (atomic number) defines the element.
Question 20. Isotopes of an element have the same:
A) Mass number
B) Number of neutrons
C) Number of protons
Question 1. Which of the following is an example of a mixture?
A) Pure sodium chloride
B) Distilled water
C) Air
D) Carbon dioxide
Answer: C
Explanation: Air is a mixture because it contains several different gases (mainly nitrogen, oxygen,
argon, carbon dioxide) that are not chemically bonded.
Question 2. What is the correct chemical formula for magnesium chloride?
A) MgCl
B) MgCl₂
C) Mg₂Cl
D) Mg₂Cl₂
Answer: B
Explanation: Magnesium forms a 2+ ion and chloride is 1-. Two chloride ions are needed to balance
one magnesium ion, giving MgCl₂.
Question 3. Which term best describes a substance consisting of two or more elements chemically
combined in fixed proportions?
A) Mixture
B) Compound
C) Solution
D) Alloy
Answer: B
Explanation: A compound is formed when two or more elements are chemically combined in a fixed
ratio.
Question 4. Which statement about the atoms in a chemical reaction is correct?
A) Atoms are destroyed.
B) Atoms are created.
C) Atoms are rearranged.
D) Atoms change into energy.
Answer: C
Explanation: In a chemical reaction, atoms are rearranged to form new substances, but are neither
created nor destroyed.
Question 5. What is Avogadro’s constant?
A) 1.008
B) 6.02 × 10²³ mol⁻¹
C) 3.14
D) 9.8 m/s²
Answer: B
, IB Chemistry (SL and HL) Examination Exam
Explanation: Avogadro’s constant is the number of particles (atoms, molecules, ions) in one mole,
which is 6.02 × 10²³.
Question 6. What is the molar mass of H₂SO₄ (sulfuric acid)?
A) 34 g/mol
B) 98 g/mol
C) 100 g/mol
D) 49 g/mol
Answer: B
Explanation: H₂SO₄ has a molar mass of (2×1) + 32 + (4×16) = 2 + 32 + 64 = 98 g/mol.
Question 7. Which of the following is the correct definition of relative atomic mass?
A) The mass of one atom in grams
B) The weighted average mass of an atom compared to 1/12 of a carbon-12 atom
C) The mass number of an atom
D) The number of neutrons in an atom
Answer: B
Explanation: Relative atomic mass is a weighted average compared to 1/12 of a carbon-12 atom.
Question 8. How many moles of oxygen atoms are there in 18 g of water (H₂O)?
A) 1
B) 2
C) 0.5
D) 3
Answer: A
Explanation: Moles of H₂O = 18/18 = 1 mol; 1 mol of H₂O contains 1 mol of O atoms.
Question 9. Which calculation would you use to find the number of particles in a 0.5 mol sample?
A) 0.5 × 6.02 × 10²³
B) 0.5 ÷ 6.02 × 10²³
C) 0.5 × 1.01
D) 0.5 ÷ 1.01
Answer: A
Explanation: Number of particles = moles × Avogadro’s constant.
Question 10. What is the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and
53.3% oxygen by mass?
A) CHO
B) CH₂O
C) C₂H₂O₂
D) C₂H₄O₂
Answer: B
, IB Chemistry (SL and HL) Examination Exam
Explanation: Divide by molar masses: C: 40/12=3.33, H: 6.7/1=6.7, O: 53.3/16=3.33. Simplest ratio is
1:2:1 (CH₂O).
Question 11. In the reaction: 2Na + Cl₂ → 2NaCl, what is the limiting reactant if 4 mol Na reacts with
2 mol Cl₂?
A) Sodium
B) Chlorine
C) Sodium chloride
D) Neither
Answer: B
Explanation: 4 mol Na requires 2 mol Cl₂ (1:1 ratio), so both are used up; neither is in excess, but Cl₂
is limiting if less is present.
Question 12. If 1.6 g of oxygen gas (O₂) reacts, how many moles of O₂ are present? (Molar mass of
O₂ = 32 g/mol)
A) 0.05
B) 0.5
C) 0.2
D) 0.04
Answer: C
Explanation: Moles = mass/molar mass = 1.6/32 = 0.05 mol.
Question 13. What is the theoretical yield of NaCl when 2.3 g of Na reacts with excess Cl₂? (Na = 23,
NaCl = 58.5)
A) 5.85 g
B) 2.3 g
C) 1.15 g
D) 5.0 g
Answer: A
Explanation: 2.3 g Na = 0.1 mol; 0.1 mol NaCl = 0.1 × 58.5 = 5.85 g.
Question 14. If the actual yield of a reaction is 4.8 g and the theoretical yield is 6.0 g, what is the
percentage yield?
A) 80%
B) 60%
C) 120%
D) 20%
Answer: A
Explanation: % yield = (actual/theoretical) × 100 = (4.8/6.0) × 100 = 80%.
Question 15. What is the concentration of a solution containing 0.5 mol NaCl in 250 cm³ of water?
A) 2 mol/dm³
, IB Chemistry (SL and HL) Examination Exam
B) 0.5 mol/dm³
C) 0.2 mol/dm³
D) 1 mol/dm³
Answer: A
Explanation: 250 cm³ = 0.25 dm³; concentration = moles/volume = 0.5/0.25 = 2 mol/dm³.
Question 16. Which equation represents the ideal gas law?
A) P = nRT/V
B) PV = nRT
C) PV = RT/n
D) V = nRT/P
Answer: B
Explanation: The ideal gas law is PV = nRT.
Question 17. What is the volume at STP (273 K, 1 atm) occupied by 2 moles of an ideal gas?
A) 11.2 L
B) 22.4 L
C) 44.8 L
D) 33.6 L
Answer: C
Explanation: 1 mol gas at STP = 22.4 L; 2 mol = 44.8 L.
Question 18. What is the mass number of an atom with 12 protons and 13 neutrons?
A) 12
B) 13
C) 25
D) 1
Answer: C
Explanation: Mass number = protons + neutrons = 12 + 13 = 25.
Question 19. Which subatomic particle determines the identity (element) of an atom?
A) Neutron
B) Proton
C) Electron
D) Nucleus
Answer: B
Explanation: The number of protons (atomic number) defines the element.
Question 20. Isotopes of an element have the same:
A) Mass number
B) Number of neutrons
C) Number of protons
