CHEM 120 Final Exam Study Guide | Most Frequently
Tested QUESTIONs & Verified Solutions 2026/2027
QUESTION 1
What is the mass percent of carbon in glucose (𝐶6 𝐻12 𝑂6 )? (Molar
masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol)
• A. 20.0%
• B. 40.0%
• C. 53.3%
• D. 60.0%
Correct Answer: B. 40.0%
Detailed Rationale: The molar mass of glucose is calculated as
(6 × 12.01) + (12 × 1.008) + (6 × 16.00) = 180.16 g/mol. The total
mass of carbon is 6 × 12.01 = 72.06 g/mol. Mass percent of carbon is
(72.06/180.16) × 100% = 40.0%.
QUESTION 2
Which of the following sets of quantum numbers (𝑛, 𝑙, 𝑚𝑙 , 𝑚𝑠 ) is
permissible for an electron in an atom?
• A. 3,2, −2, +1/2
• B. 2,2,0, −1/2
• C. 1,1,0, +1/2
• D. 3,0,1, −1/2
,Correct Answer: A. 3,2, −2, +1/2
Detailed Rationale: For a given principal quantum number 𝑛, the
angular momentum quantum number 𝑙 can range from 0 to 𝑛 − 1. For
𝑛 = 3, 𝑙 can be 0,1, or 2. The magnetic quantum number 𝑚𝑙 ranges
from −𝑙 to +𝑙; for 𝑙 = 2, 𝑚𝑙 can be −2, −1,0, +1, +2. Therefore, the
set 3,2, −2, +1/2 is valid. Option B is invalid because 𝑙 cannot equal 𝑛.
Option C is invalid because 𝑙 must be less than 𝑛. Option D is invalid
because 𝑚𝑙 cannot exceed 𝑙 in magnitude when 𝑙 = 0.
QUESTION 3
Which of the following atoms or ions has the largest radius?
• A. 𝑁𝑎+
• B. 𝑀𝑔2+
• C. 𝐹 −
• D. 𝑂2−
Correct Answer: D. 𝑂2−
Detailed Rationale: Isoelectronic species have the same number of
electrons. 𝑁𝑎+ (10 electrons), 𝑀𝑔2+ (10 electrons), 𝐹 − (10 electrons),
and 𝑂2− (10 electrons) are all isoelectronic with neon. As nuclear
charge (atomic number) increases among isoelectronic species, the pull
on the electrons increases, making the radius smaller. 𝑂2− has the
smallest atomic number (𝑍 = 8), resulting in the weakest effective
nuclear attraction and thus the largest ionic radius.
QUESTION 4
,According to VSEPR theory, what is the molecular geometry of a 𝑆𝐹4
molecule?
• A. Tetrahedral
• B. Square planar
• C. Seesaw
• D. Trigonal bipyramidal
Correct Answer: C. Seesaw
Detailed Rationale: Sulfur tetrafluoride (𝑆𝐹4 ) has 6 + 4(7) = 34
valence electrons. Sulfur is the central atom, bonded to 4 fluorine
atoms with 1 lone pair on the sulfur atom. This gives an electronic
geometry of trigonal bipyramidal with one equatorial position occupied
by a lone pair, resulting in a seesaw molecular shape.
QUESTION 5
Which of the following substances exhibits hydrogen bonding as its
primary intermolecular force in the pure liquid state?
• A. 𝐶𝐻4
• B. 𝐻2 𝑆
• C. 𝑁𝐻3
• D. 𝑃𝐻3
Correct Answer: C. 𝑁𝐻3
Detailed Rationale: Hydrogen bonding occurs when hydrogen is
covalently bonded to highly electronegative atoms with lone pairs,
specifically nitrogen, oxygen, or fluorine (𝑁, 𝑂, 𝐹). Ammonia (𝑁𝐻3 )
, features 𝑁 − 𝐻 bonds, allowing strong hydrogen bonding between
molecules. The others lack 𝑁, 𝑂, or 𝐹 bonded directly to hydrogen.
QUESTION 6
A sample of an ideal gas occupies 4.00 L at 300 K and 1.00 atm. What
will be its volume at 300 K and 2.00 atm?
• A. 2.00 L
• B. 4.00 L
• C. 8.00 L
• D. 16.0 L
Correct Answer: A. 2.00 L
Detailed Rationale: According to Boyle's Law, pressure and volume are
inversely proportional at constant temperature (𝑃1 𝑉1 = 𝑃2 𝑉2 ). Doubling
the pressure from 1.00 atm to 2.00 atm while keeping temperature
constant cuts the volume in half, from 4.00 L to 2.00 L.
QUESTION 7
Given the thermochemical equation 2𝐻2 (𝑔) + 𝑂2 (𝑔) → 2𝐻2 𝑂(𝑙) with
Δ𝐻 ∘ = −572 kJ/mol, how much heat is released when 9.00 grams of
𝐻2 reacts completely with excess oxygen? (Molar mass of 𝐻2 = 2.016
g/mol)
• A. 572 kJ
• B. 1144 kJ
• C. 1277 kJ
• D. 2554 kJ
Tested QUESTIONs & Verified Solutions 2026/2027
QUESTION 1
What is the mass percent of carbon in glucose (𝐶6 𝐻12 𝑂6 )? (Molar
masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol)
• A. 20.0%
• B. 40.0%
• C. 53.3%
• D. 60.0%
Correct Answer: B. 40.0%
Detailed Rationale: The molar mass of glucose is calculated as
(6 × 12.01) + (12 × 1.008) + (6 × 16.00) = 180.16 g/mol. The total
mass of carbon is 6 × 12.01 = 72.06 g/mol. Mass percent of carbon is
(72.06/180.16) × 100% = 40.0%.
QUESTION 2
Which of the following sets of quantum numbers (𝑛, 𝑙, 𝑚𝑙 , 𝑚𝑠 ) is
permissible for an electron in an atom?
• A. 3,2, −2, +1/2
• B. 2,2,0, −1/2
• C. 1,1,0, +1/2
• D. 3,0,1, −1/2
,Correct Answer: A. 3,2, −2, +1/2
Detailed Rationale: For a given principal quantum number 𝑛, the
angular momentum quantum number 𝑙 can range from 0 to 𝑛 − 1. For
𝑛 = 3, 𝑙 can be 0,1, or 2. The magnetic quantum number 𝑚𝑙 ranges
from −𝑙 to +𝑙; for 𝑙 = 2, 𝑚𝑙 can be −2, −1,0, +1, +2. Therefore, the
set 3,2, −2, +1/2 is valid. Option B is invalid because 𝑙 cannot equal 𝑛.
Option C is invalid because 𝑙 must be less than 𝑛. Option D is invalid
because 𝑚𝑙 cannot exceed 𝑙 in magnitude when 𝑙 = 0.
QUESTION 3
Which of the following atoms or ions has the largest radius?
• A. 𝑁𝑎+
• B. 𝑀𝑔2+
• C. 𝐹 −
• D. 𝑂2−
Correct Answer: D. 𝑂2−
Detailed Rationale: Isoelectronic species have the same number of
electrons. 𝑁𝑎+ (10 electrons), 𝑀𝑔2+ (10 electrons), 𝐹 − (10 electrons),
and 𝑂2− (10 electrons) are all isoelectronic with neon. As nuclear
charge (atomic number) increases among isoelectronic species, the pull
on the electrons increases, making the radius smaller. 𝑂2− has the
smallest atomic number (𝑍 = 8), resulting in the weakest effective
nuclear attraction and thus the largest ionic radius.
QUESTION 4
,According to VSEPR theory, what is the molecular geometry of a 𝑆𝐹4
molecule?
• A. Tetrahedral
• B. Square planar
• C. Seesaw
• D. Trigonal bipyramidal
Correct Answer: C. Seesaw
Detailed Rationale: Sulfur tetrafluoride (𝑆𝐹4 ) has 6 + 4(7) = 34
valence electrons. Sulfur is the central atom, bonded to 4 fluorine
atoms with 1 lone pair on the sulfur atom. This gives an electronic
geometry of trigonal bipyramidal with one equatorial position occupied
by a lone pair, resulting in a seesaw molecular shape.
QUESTION 5
Which of the following substances exhibits hydrogen bonding as its
primary intermolecular force in the pure liquid state?
• A. 𝐶𝐻4
• B. 𝐻2 𝑆
• C. 𝑁𝐻3
• D. 𝑃𝐻3
Correct Answer: C. 𝑁𝐻3
Detailed Rationale: Hydrogen bonding occurs when hydrogen is
covalently bonded to highly electronegative atoms with lone pairs,
specifically nitrogen, oxygen, or fluorine (𝑁, 𝑂, 𝐹). Ammonia (𝑁𝐻3 )
, features 𝑁 − 𝐻 bonds, allowing strong hydrogen bonding between
molecules. The others lack 𝑁, 𝑂, or 𝐹 bonded directly to hydrogen.
QUESTION 6
A sample of an ideal gas occupies 4.00 L at 300 K and 1.00 atm. What
will be its volume at 300 K and 2.00 atm?
• A. 2.00 L
• B. 4.00 L
• C. 8.00 L
• D. 16.0 L
Correct Answer: A. 2.00 L
Detailed Rationale: According to Boyle's Law, pressure and volume are
inversely proportional at constant temperature (𝑃1 𝑉1 = 𝑃2 𝑉2 ). Doubling
the pressure from 1.00 atm to 2.00 atm while keeping temperature
constant cuts the volume in half, from 4.00 L to 2.00 L.
QUESTION 7
Given the thermochemical equation 2𝐻2 (𝑔) + 𝑂2 (𝑔) → 2𝐻2 𝑂(𝑙) with
Δ𝐻 ∘ = −572 kJ/mol, how much heat is released when 9.00 grams of
𝐻2 reacts completely with excess oxygen? (Molar mass of 𝐻2 = 2.016
g/mol)
• A. 572 kJ
• B. 1144 kJ
• C. 1277 kJ
• D. 2554 kJ
