Chem 103 Modules 1–6 & Final Exam | Latest Update 2026/2027 |
Questions and Verified Answers with Rationales | 100% Correct
1. Which property of matter can be observed without changing its chemical identity?
A) Flammability
B) Reactivity with acid
C) Boiling point
D) Toxicity
Correct Answer: C
Rationale: Physical properties are those that can be observed or measured without altering the
substance’s chemical composition. Boiling point is a physical property; the others involve chemical
reactions. Different states of matter have distinct particle arrangements and energies.
2. How many significant figures are in the measurement 0.003050 m?
A) 3
B) 4
C) 5
D) 6
Correct Answer: B
Rationale: Leading zeros are not significant (0.003), the digits 3,0,5,0 include captive zeros (between
non-zeros) as significant. Trailing zeros after a decimal point are significant, so this has 4 significant
figures. In general, zeros after a decimal and after non-zero digits are significant, while leading zeros are
not.
3. Convert 4.58 × 10³ cm³ to the following unit:
A) 4.58 × 10⁹ m³
,B) 4.58 × 10⁵ m³
C) 4.58 × 10⁻³ m³
D) 4.58 × 10⁶ m³
Correct Answer: C
Rationale: Using the conversion factor 10⁶ cm³ = 1 m³. Therefore, 4.58 × 10³ cm³ × (1 m³ / 10⁶ cm³) =
4.58 × 10⁻³ m³.
4. A student measures the mass of a beaker three times: 25.45 g, 25.46 g, and 25.44 g. The known mass
of the beaker is 25.50 g. The measurements are:
A) Precise but not accurate
B) Accurate but not precise
C) Both accurate and precise
D) Neither accurate nor precise
Correct Answer: A
Rationale: The measurements are very close to each other (precise) but differ from the true value (not
accurate). Accuracy refers to closeness to the true value, precision to reproducibility.
5. Dimensional analysis is used to convert units. Which statement is true?
A) Conversion factors are ratios of equivalent quantities measured in different units.
B) Units do not need to cancel when setting up dimensional analysis.
C) Dimensional analysis cannot be used for multi-step conversions.
D) The conversion factor is always less than 1.
Correct Answer: A
,Rationale: Dimensional analysis uses conversion factors as ratios of equivalent quantities. Units are set
up to cancel, leaving the desired unit.
6. The mass number of an atom is equal to:
A) The number of protons only
B) The number of neutrons only
C) The sum of protons and neutrons
D) The atomic number minus the charge
Correct Answer: C
Rationale: The mass number (A) is the total number of protons and neutrons in the nucleus. The atomic
number (Z) is the number of protons. The number of neutrons is A – Z.
7. Which of the following is TRUE about isotopes?
A) Isotopes have the same number of protons but different numbers of neutrons.
B) Isotopes have the same number of neutrons but different numbers of protons.
C) Isotopes have the same mass number but different atomic numbers.
D) Isotopes are always radioactive.
Correct Answer: A
Rationale: Isotopes have the same atomic number (same number of protons) but different numbers of
neutrons. Isotopes may be stable or radioactive.
8. The Bohr model of the atom describes electrons in:
A) Fixed orbits around the nucleus
B) Randomly distributed clouds
C) An electron sea without structure
D) Subshells with specific quantum numbers
, Correct Answer: A
Rationale: The Bohr model (1913) describes electrons traveling in fixed circular orbits around the
nucleus at specific energy levels. Later quantum mechanical models revised this picture.
9. Which subatomic particle has the smallest mass?
A) Proton
B) Neutron
C) Electron
D) They have the same mass
Correct Answer: C
Rationale: The electron has a mass of approximately 9.11 × 10⁻³¹ kg, which is about 1/1836 the mass of a
proton or neutron. Protons and neutrons have nearly equal masses (≈1.67 × 10⁻²⁷ kg).
10. According to the Pauli exclusion principle:
A) No two electrons in the same atom can have the same set of four quantum numbers.
B) Two electrons in the same orbital must spin in the same direction.
C) All orbitals in a subshell must be singly occupied before any is doubly occupied.
D) Electrons fill the lowest energy orbitals first.
Correct Answer: A
Rationale: Pauli Exclusion Principle states that no two electrons can have identical quantum numbers.
Consequently, any orbital can hold a maximum of two electrons, and they must have opposite spins.
11. Which of the following correctly gives the number of valence electrons for a Group 2 element?
A) 1
Questions and Verified Answers with Rationales | 100% Correct
1. Which property of matter can be observed without changing its chemical identity?
A) Flammability
B) Reactivity with acid
C) Boiling point
D) Toxicity
Correct Answer: C
Rationale: Physical properties are those that can be observed or measured without altering the
substance’s chemical composition. Boiling point is a physical property; the others involve chemical
reactions. Different states of matter have distinct particle arrangements and energies.
2. How many significant figures are in the measurement 0.003050 m?
A) 3
B) 4
C) 5
D) 6
Correct Answer: B
Rationale: Leading zeros are not significant (0.003), the digits 3,0,5,0 include captive zeros (between
non-zeros) as significant. Trailing zeros after a decimal point are significant, so this has 4 significant
figures. In general, zeros after a decimal and after non-zero digits are significant, while leading zeros are
not.
3. Convert 4.58 × 10³ cm³ to the following unit:
A) 4.58 × 10⁹ m³
,B) 4.58 × 10⁵ m³
C) 4.58 × 10⁻³ m³
D) 4.58 × 10⁶ m³
Correct Answer: C
Rationale: Using the conversion factor 10⁶ cm³ = 1 m³. Therefore, 4.58 × 10³ cm³ × (1 m³ / 10⁶ cm³) =
4.58 × 10⁻³ m³.
4. A student measures the mass of a beaker three times: 25.45 g, 25.46 g, and 25.44 g. The known mass
of the beaker is 25.50 g. The measurements are:
A) Precise but not accurate
B) Accurate but not precise
C) Both accurate and precise
D) Neither accurate nor precise
Correct Answer: A
Rationale: The measurements are very close to each other (precise) but differ from the true value (not
accurate). Accuracy refers to closeness to the true value, precision to reproducibility.
5. Dimensional analysis is used to convert units. Which statement is true?
A) Conversion factors are ratios of equivalent quantities measured in different units.
B) Units do not need to cancel when setting up dimensional analysis.
C) Dimensional analysis cannot be used for multi-step conversions.
D) The conversion factor is always less than 1.
Correct Answer: A
,Rationale: Dimensional analysis uses conversion factors as ratios of equivalent quantities. Units are set
up to cancel, leaving the desired unit.
6. The mass number of an atom is equal to:
A) The number of protons only
B) The number of neutrons only
C) The sum of protons and neutrons
D) The atomic number minus the charge
Correct Answer: C
Rationale: The mass number (A) is the total number of protons and neutrons in the nucleus. The atomic
number (Z) is the number of protons. The number of neutrons is A – Z.
7. Which of the following is TRUE about isotopes?
A) Isotopes have the same number of protons but different numbers of neutrons.
B) Isotopes have the same number of neutrons but different numbers of protons.
C) Isotopes have the same mass number but different atomic numbers.
D) Isotopes are always radioactive.
Correct Answer: A
Rationale: Isotopes have the same atomic number (same number of protons) but different numbers of
neutrons. Isotopes may be stable or radioactive.
8. The Bohr model of the atom describes electrons in:
A) Fixed orbits around the nucleus
B) Randomly distributed clouds
C) An electron sea without structure
D) Subshells with specific quantum numbers
, Correct Answer: A
Rationale: The Bohr model (1913) describes electrons traveling in fixed circular orbits around the
nucleus at specific energy levels. Later quantum mechanical models revised this picture.
9. Which subatomic particle has the smallest mass?
A) Proton
B) Neutron
C) Electron
D) They have the same mass
Correct Answer: C
Rationale: The electron has a mass of approximately 9.11 × 10⁻³¹ kg, which is about 1/1836 the mass of a
proton or neutron. Protons and neutrons have nearly equal masses (≈1.67 × 10⁻²⁷ kg).
10. According to the Pauli exclusion principle:
A) No two electrons in the same atom can have the same set of four quantum numbers.
B) Two electrons in the same orbital must spin in the same direction.
C) All orbitals in a subshell must be singly occupied before any is doubly occupied.
D) Electrons fill the lowest energy orbitals first.
Correct Answer: A
Rationale: Pauli Exclusion Principle states that no two electrons can have identical quantum numbers.
Consequently, any orbital can hold a maximum of two electrons, and they must have opposite spins.
11. Which of the following correctly gives the number of valence electrons for a Group 2 element?
A) 1
