CHEM 103 Final Exam | General Chemistry I w/Lab
Exam Q&A | Portage Learning
1. Which of the following best describes the Law of Definite Proportions?
A) A compound always contains the same elements in the same
proportion by
mass.
B) The total mass of reactants equals the total mass of products in a
chemical
reaction.
C) Atoms of different elements combine in small whole-number ratios to
form
compounds.
D) The energy of a system is conserved during a chemical change.
Correct Answer: A compound always contains the same elements in the same
proportion by mass.
Rationale: The Law of Definite Proportions, also known as the Law of Constant
Composition, states that a given chemical compound always contains its
component elements in a fixed ratio by mass, regardless of its source or
preparation method. This law was established by Joseph Proust and is
fundamental to understanding chemical formulas. The other options describe
the Law of Conservation of Mass, the Law of Multiple Proportions, and the Law
of Conservation of Energy, respectively.
2. What is the primary function of the neutron in an atom? A) It determines
the atomic number of the element.
B) It contributes to the mass of the atom and stabilizes the nucleus.
C) It balances the charge of the protons in the nucleus.
D) It participates in chemical bonding with other atoms.
Correct Answer: It contributes to the mass of the atom and stabilizes the
nucleus.
Rationale: Neutrons are neutral subatomic particles located in the atomic
nucleus. They contribute significantly to the atomic mass and help stabilize the
nucleus by offsetting the repulsive forces between positively charged protons.
Neutrons do not determine the atomic number (that is the proton's role), do
,not balance charge (they are neutral), and do not participate in chemical
bonding.
3. According to the quantum mechanical model, what does the principal
quantum number (n) represent?
A) The shape of an orbital.
B) The orientation of an orbital in space.
C) The main energy level or shell of an electron.
D) The spin of an electron.
Correct Answer: The main energy level or shell of an electron.
Rationale: In the quantum mechanical model, the principal quantum number
(n) designates the principal energy level or shell of an electron and is related to
the average distance of the electron from the nucleus. The angular momentum
quantum number (l) determines orbital shape, the magnetic quantum number
(m_l) describes orbital orientation, and the spin quantum number (m_s)
describes electron spin.
4. A researcher is studying periodic trends and observes that atomic radius
decreases across a period from left to right. Which factor primarily
explains this trend?
A) Increasing nuclear charge pulls electrons closer to the nucleus.
B) Adding electrons to the same shell increases electron-electron
repulsion.
C) The number of energy levels increases across a period.
D) Shielding effect increases across a period.
Correct Answer: Increasing nuclear charge pulls electrons closer to the nucleus.
Rationale: Across a period, protons are added to the nucleus while electrons
are added to the same principal energy level. The increasing nuclear charge
exerts a stronger attractive pull on the electrons, drawing them closer to the
nucleus and decreasing the atomic radius. Electron-electron repulsion and
shielding do not increase across a period in a way that would cause expansion.
5. Which term refers to the energy required to remove an electron from a
gaseous atom or ion?
A) Electron affinity
, B) Electronegativity
C) Ionization energy
D) Lattice energy
Correct Answer: Ionization energy
Rationale: Ionization energy is defined as the minimum energy required to
remove the most loosely bound electron from a neutral gaseous atom or ion.
Electron affinity is the energy change when an atom gains an electron,
electronegativity measures an atom's tendency to attract shared electrons in a
bond, and lattice energy is the energy released when ions form a crystalline
lattice.
6. What is the correct electron configuration for a neutral chlorine atom (Z
= 17)?
A) 1s² 2s² 2p⁶ 3s² 3p⁵
B) 1s² 2s² 2p⁶ 3s² 3p⁶
C) 1s² 2s² 2p⁵ 3s² 3p⁶
D) 1s² 2s² 2p⁶ 3s² 3p⁴
Correct Answer: 1s² 2s² 2p⁶ 3s² 3p⁵
Rationale: Chlorine has 17 electrons. Filling orbitals according to the Aufbau
principle: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁵ (17). Option B represents argon
(18 electrons), option C is not a valid configuration, and option D represents
sulfur (16 electrons).
7. Which principle explains why electrons fill the lowest energy orbitals
first?
A) Hund's rule
B) Pauli exclusion principle
C) Aufbau principle
D) Heisenberg uncertainty principle
Correct Answer: Aufbau principle
Rationale: The Aufbau principle states that electrons occupy the lowest
available energy orbitals before filling higher energy orbitals. Hund's rule
addresses electron distribution within degenerate orbitals, the Pauli exclusion
principle states that no two electrons can have the same four quantum
, numbers, and the Heisenberg uncertainty principle relates to the limits of
simultaneously knowing position and momentum.
8. The nurse is reviewing a patient's lab report and notes a value of 0.00045
M for a medication concentration. How is this value correctly expressed
in scientific notation? A) 4.5 × 10⁻⁴
B) 45 × 10⁻⁵
C) 4.5 × 10⁴
D) 0.45 × 10⁻³
Correct Answer: 4.5 × 10⁻⁴
Rationale: To convert 0.00045 to scientific notation, move the decimal point
four places to the right to obtain 4.5. Because the original number is less than
1, the exponent is negative four. Option B is not in proper scientific notation
(coefficient must be between 1 and 10), option C has a positive exponent, and
option D is not in standard form.
9. What is the molecular geometry of a molecule with the VSEPR formula
AX₃E (three bonding pairs and one lone pair on the central atom)?
A) Tetrahedral
B) Trigonal pyramidal
C) Trigonal planar
D) Bent
Correct Answer: Trigonal pyramidal
Rationale: The VSEPR formula AX₃E indicates three bonding pairs and one lone
pair on the central atom. The electron geometry is tetrahedral, but the
molecular geometry (considering only atoms) is trigonal pyramidal, as seen in
ammonia (NH₃). Trigonal planar would be AX₃ with no lone pairs, bent would
be AX₂E₂, and tetrahedral would be AX₄.
10. Which type of intermolecular force is primarily responsible for the high
boiling point of water compared to hydrogen sulfide (H₂S)?
A) London dispersion forces
B) Dipole-dipole interactions
C) Hydrogen bonding
D) Ion-dipole interactions
Exam Q&A | Portage Learning
1. Which of the following best describes the Law of Definite Proportions?
A) A compound always contains the same elements in the same
proportion by
mass.
B) The total mass of reactants equals the total mass of products in a
chemical
reaction.
C) Atoms of different elements combine in small whole-number ratios to
form
compounds.
D) The energy of a system is conserved during a chemical change.
Correct Answer: A compound always contains the same elements in the same
proportion by mass.
Rationale: The Law of Definite Proportions, also known as the Law of Constant
Composition, states that a given chemical compound always contains its
component elements in a fixed ratio by mass, regardless of its source or
preparation method. This law was established by Joseph Proust and is
fundamental to understanding chemical formulas. The other options describe
the Law of Conservation of Mass, the Law of Multiple Proportions, and the Law
of Conservation of Energy, respectively.
2. What is the primary function of the neutron in an atom? A) It determines
the atomic number of the element.
B) It contributes to the mass of the atom and stabilizes the nucleus.
C) It balances the charge of the protons in the nucleus.
D) It participates in chemical bonding with other atoms.
Correct Answer: It contributes to the mass of the atom and stabilizes the
nucleus.
Rationale: Neutrons are neutral subatomic particles located in the atomic
nucleus. They contribute significantly to the atomic mass and help stabilize the
nucleus by offsetting the repulsive forces between positively charged protons.
Neutrons do not determine the atomic number (that is the proton's role), do
,not balance charge (they are neutral), and do not participate in chemical
bonding.
3. According to the quantum mechanical model, what does the principal
quantum number (n) represent?
A) The shape of an orbital.
B) The orientation of an orbital in space.
C) The main energy level or shell of an electron.
D) The spin of an electron.
Correct Answer: The main energy level or shell of an electron.
Rationale: In the quantum mechanical model, the principal quantum number
(n) designates the principal energy level or shell of an electron and is related to
the average distance of the electron from the nucleus. The angular momentum
quantum number (l) determines orbital shape, the magnetic quantum number
(m_l) describes orbital orientation, and the spin quantum number (m_s)
describes electron spin.
4. A researcher is studying periodic trends and observes that atomic radius
decreases across a period from left to right. Which factor primarily
explains this trend?
A) Increasing nuclear charge pulls electrons closer to the nucleus.
B) Adding electrons to the same shell increases electron-electron
repulsion.
C) The number of energy levels increases across a period.
D) Shielding effect increases across a period.
Correct Answer: Increasing nuclear charge pulls electrons closer to the nucleus.
Rationale: Across a period, protons are added to the nucleus while electrons
are added to the same principal energy level. The increasing nuclear charge
exerts a stronger attractive pull on the electrons, drawing them closer to the
nucleus and decreasing the atomic radius. Electron-electron repulsion and
shielding do not increase across a period in a way that would cause expansion.
5. Which term refers to the energy required to remove an electron from a
gaseous atom or ion?
A) Electron affinity
, B) Electronegativity
C) Ionization energy
D) Lattice energy
Correct Answer: Ionization energy
Rationale: Ionization energy is defined as the minimum energy required to
remove the most loosely bound electron from a neutral gaseous atom or ion.
Electron affinity is the energy change when an atom gains an electron,
electronegativity measures an atom's tendency to attract shared electrons in a
bond, and lattice energy is the energy released when ions form a crystalline
lattice.
6. What is the correct electron configuration for a neutral chlorine atom (Z
= 17)?
A) 1s² 2s² 2p⁶ 3s² 3p⁵
B) 1s² 2s² 2p⁶ 3s² 3p⁶
C) 1s² 2s² 2p⁵ 3s² 3p⁶
D) 1s² 2s² 2p⁶ 3s² 3p⁴
Correct Answer: 1s² 2s² 2p⁶ 3s² 3p⁵
Rationale: Chlorine has 17 electrons. Filling orbitals according to the Aufbau
principle: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁵ (17). Option B represents argon
(18 electrons), option C is not a valid configuration, and option D represents
sulfur (16 electrons).
7. Which principle explains why electrons fill the lowest energy orbitals
first?
A) Hund's rule
B) Pauli exclusion principle
C) Aufbau principle
D) Heisenberg uncertainty principle
Correct Answer: Aufbau principle
Rationale: The Aufbau principle states that electrons occupy the lowest
available energy orbitals before filling higher energy orbitals. Hund's rule
addresses electron distribution within degenerate orbitals, the Pauli exclusion
principle states that no two electrons can have the same four quantum
, numbers, and the Heisenberg uncertainty principle relates to the limits of
simultaneously knowing position and momentum.
8. The nurse is reviewing a patient's lab report and notes a value of 0.00045
M for a medication concentration. How is this value correctly expressed
in scientific notation? A) 4.5 × 10⁻⁴
B) 45 × 10⁻⁵
C) 4.5 × 10⁴
D) 0.45 × 10⁻³
Correct Answer: 4.5 × 10⁻⁴
Rationale: To convert 0.00045 to scientific notation, move the decimal point
four places to the right to obtain 4.5. Because the original number is less than
1, the exponent is negative four. Option B is not in proper scientific notation
(coefficient must be between 1 and 10), option C has a positive exponent, and
option D is not in standard form.
9. What is the molecular geometry of a molecule with the VSEPR formula
AX₃E (three bonding pairs and one lone pair on the central atom)?
A) Tetrahedral
B) Trigonal pyramidal
C) Trigonal planar
D) Bent
Correct Answer: Trigonal pyramidal
Rationale: The VSEPR formula AX₃E indicates three bonding pairs and one lone
pair on the central atom. The electron geometry is tetrahedral, but the
molecular geometry (considering only atoms) is trigonal pyramidal, as seen in
ammonia (NH₃). Trigonal planar would be AX₃ with no lone pairs, bent would
be AX₂E₂, and tetrahedral would be AX₄.
10. Which type of intermolecular force is primarily responsible for the high
boiling point of water compared to hydrogen sulfide (H₂S)?
A) London dispersion forces
B) Dipole-dipole interactions
C) Hydrogen bonding
D) Ion-dipole interactions
