CHEM 120 QUESTION Bank | Complete Practice Test
with Verified Answers & Expert Rationales
2026/2027
QUESTION 1
A student measures the mass of a metal sample as 12.450 g and its
volume as 4.50 mL. How should the calculated density be reported with
the correct number of significant figures?
• A. 2.7667 g/mL
• B. 2.767 g/mL
• C. 2.77 g/mL
• D. 2.8 g/mL
Correct Answer: C. 2.77 g/mL
Detailed Rationale: In division, the result must have the same number
of significant figures as the measurement with the fewest significant
figures. The mass (12.450) has five, while the volume (4.50) has three.
Therefore, the density (12.450/4.50 = 2.7666. ..) must be rounded to
three significant figures, resulting in 2.77 g/mL.
QUESTION 2
An isotope of an element contains 35 protons, 45 neutrons, and 36
electrons. What is the correct identity and charge of this species?
• A. 80
35𝐵 𝑟
+
, • B. 80
35𝐵 𝑟
−
• C. 80
45𝑅 ℎ
+
• D. 45
35𝐵 𝑟
−
Correct Answer: B. 80
35𝐵 𝑟
−
Detailed Rationale: The number of protons (35) identifies the element
as Bromine (𝐵𝑟). The mass number is the sum of protons and neutrons
(35 + 45 = 80). Since there is one more electron (36) than protons
(35), the species carries a −1 charge.
QUESTION 3
What is the correct IUPAC name for the compound 𝑁2 𝑂4 ?
• A. Nitrogen oxide
• B. Dinitrogen oxide
• C. Dinitrogen tetroxide
• D. Nitrogen(IV) oxide
Correct Answer: C. Dinitrogen tetroxide
Detailed Rationale: 𝑁2 𝑂4 is a binary molecular compound (two non-
metals). For these compounds, Greek prefixes are used to indicate the
number of atoms. "Di-" indicates two nitrogens and "tetra-" (shortened
to "tetr-" before an 'o') indicates four oxygens.
QUESTION 4
How many carbon atoms are present in a 5.00 g sample of pure
graphite (carbon)? (Molar mass of C = 12.01 g/mol)
• A. 2.51 × 1023 atoms
, • B. 4.16 × 1023 atoms
• C. 6.02 × 1023 atoms
• D. 1.20 × 1024 atoms
Correct Answer: A. 2.51 × 1023 atoms
Detailed Rationale: First, convert mass to moles: 5.00 g/12.01 g/mol =
0.4163 mol. Then, convert moles to atoms using Avogadro’s number:
0.4163 mol × (6.022 × 1023 atoms/mol) = 2.51 × 1023 atoms.
QUESTION 5
A compound is found to be 82.7% carbon and 17.3% hydrogen by
mass. What is its empirical formula? (Molar masses: C = 12.01 g/mol, H
= 1.008 g/mol)
• A. 𝐶𝐻2
• B. 𝐶𝐻3
• C. 𝐶2 𝐻5
• D. 𝐶3 𝐻8
Correct Answer: C. 𝐶2 𝐻5
Detailed Rationale: In 100 g: moles C = 82.7/12.01 = 6.886 mol;
moles H = 17.3/1.008 = 17.16 mol. Dividing both by the smaller value
(6.886): C = 1, H = 2.49. Since 2.49 is close to 2.5 (5/2), multiply the
ratio by 2 to get integers: 𝐶2 𝐻5 .
QUESTION 6
, When 10.0 g of 𝐶𝐻4 is burned in excess 𝑂2 , the actual yield of 𝐶𝑂2 is
22.0 g. What is the percent yield? (𝐶𝐻4 + 2𝑂2 → 𝐶𝑂2 + 2𝐻2 𝑂; Molar
masses: 𝐶𝐻4 = 16.04 g/mol, 𝐶𝑂2 = 44.01 g/mol)
• A. 75.0%
• B. 80.2%
• C. 92.5%
• D. 100%
Correct Answer: B. 80.2%
Detailed Rationale: Theoretical yield: 10.0 g 𝐶𝐻4 × (1 mol 𝐶𝐻4 /
16.04 g) × (1 mol 𝐶𝑂2 /1 mol 𝐶𝐻4 ) × (44.01 g 𝐶𝑂2 /1 mol) = 27.44 g.
Percent yield = (Actual/Theoretical) × 100 = (22.0/27.44) × 100 =
80.2%.
QUESTION 7
Which of the following compounds is insoluble in water according to
general solubility rules?
• A. 𝑁𝑎2 𝐶𝑂3
• B. (𝑁𝐻4 )2 𝑆
• C. 𝑃𝑏𝐶𝑙2
• D. 𝐿𝑖𝑁𝑂3
Correct Answer: C. 𝑃𝑏𝐶𝑙2
Detailed Rationale: Chlorides are generally soluble except when paired
with 𝐴𝑔+ , 𝑃𝑏 2+ , or 𝐻𝑔22+ . Compounds containing 𝑁𝑎+ , 𝐿𝑖 + , or 𝑁𝐻4+
are almost always soluble.
with Verified Answers & Expert Rationales
2026/2027
QUESTION 1
A student measures the mass of a metal sample as 12.450 g and its
volume as 4.50 mL. How should the calculated density be reported with
the correct number of significant figures?
• A. 2.7667 g/mL
• B. 2.767 g/mL
• C. 2.77 g/mL
• D. 2.8 g/mL
Correct Answer: C. 2.77 g/mL
Detailed Rationale: In division, the result must have the same number
of significant figures as the measurement with the fewest significant
figures. The mass (12.450) has five, while the volume (4.50) has three.
Therefore, the density (12.450/4.50 = 2.7666. ..) must be rounded to
three significant figures, resulting in 2.77 g/mL.
QUESTION 2
An isotope of an element contains 35 protons, 45 neutrons, and 36
electrons. What is the correct identity and charge of this species?
• A. 80
35𝐵 𝑟
+
, • B. 80
35𝐵 𝑟
−
• C. 80
45𝑅 ℎ
+
• D. 45
35𝐵 𝑟
−
Correct Answer: B. 80
35𝐵 𝑟
−
Detailed Rationale: The number of protons (35) identifies the element
as Bromine (𝐵𝑟). The mass number is the sum of protons and neutrons
(35 + 45 = 80). Since there is one more electron (36) than protons
(35), the species carries a −1 charge.
QUESTION 3
What is the correct IUPAC name for the compound 𝑁2 𝑂4 ?
• A. Nitrogen oxide
• B. Dinitrogen oxide
• C. Dinitrogen tetroxide
• D. Nitrogen(IV) oxide
Correct Answer: C. Dinitrogen tetroxide
Detailed Rationale: 𝑁2 𝑂4 is a binary molecular compound (two non-
metals). For these compounds, Greek prefixes are used to indicate the
number of atoms. "Di-" indicates two nitrogens and "tetra-" (shortened
to "tetr-" before an 'o') indicates four oxygens.
QUESTION 4
How many carbon atoms are present in a 5.00 g sample of pure
graphite (carbon)? (Molar mass of C = 12.01 g/mol)
• A. 2.51 × 1023 atoms
, • B. 4.16 × 1023 atoms
• C. 6.02 × 1023 atoms
• D. 1.20 × 1024 atoms
Correct Answer: A. 2.51 × 1023 atoms
Detailed Rationale: First, convert mass to moles: 5.00 g/12.01 g/mol =
0.4163 mol. Then, convert moles to atoms using Avogadro’s number:
0.4163 mol × (6.022 × 1023 atoms/mol) = 2.51 × 1023 atoms.
QUESTION 5
A compound is found to be 82.7% carbon and 17.3% hydrogen by
mass. What is its empirical formula? (Molar masses: C = 12.01 g/mol, H
= 1.008 g/mol)
• A. 𝐶𝐻2
• B. 𝐶𝐻3
• C. 𝐶2 𝐻5
• D. 𝐶3 𝐻8
Correct Answer: C. 𝐶2 𝐻5
Detailed Rationale: In 100 g: moles C = 82.7/12.01 = 6.886 mol;
moles H = 17.3/1.008 = 17.16 mol. Dividing both by the smaller value
(6.886): C = 1, H = 2.49. Since 2.49 is close to 2.5 (5/2), multiply the
ratio by 2 to get integers: 𝐶2 𝐻5 .
QUESTION 6
, When 10.0 g of 𝐶𝐻4 is burned in excess 𝑂2 , the actual yield of 𝐶𝑂2 is
22.0 g. What is the percent yield? (𝐶𝐻4 + 2𝑂2 → 𝐶𝑂2 + 2𝐻2 𝑂; Molar
masses: 𝐶𝐻4 = 16.04 g/mol, 𝐶𝑂2 = 44.01 g/mol)
• A. 75.0%
• B. 80.2%
• C. 92.5%
• D. 100%
Correct Answer: B. 80.2%
Detailed Rationale: Theoretical yield: 10.0 g 𝐶𝐻4 × (1 mol 𝐶𝐻4 /
16.04 g) × (1 mol 𝐶𝑂2 /1 mol 𝐶𝐻4 ) × (44.01 g 𝐶𝑂2 /1 mol) = 27.44 g.
Percent yield = (Actual/Theoretical) × 100 = (22.0/27.44) × 100 =
80.2%.
QUESTION 7
Which of the following compounds is insoluble in water according to
general solubility rules?
• A. 𝑁𝑎2 𝐶𝑂3
• B. (𝑁𝐻4 )2 𝑆
• C. 𝑃𝑏𝐶𝑙2
• D. 𝐿𝑖𝑁𝑂3
Correct Answer: C. 𝑃𝑏𝐶𝑙2
Detailed Rationale: Chlorides are generally soluble except when paired
with 𝐴𝑔+ , 𝑃𝑏 2+ , or 𝐻𝑔22+ . Compounds containing 𝑁𝑎+ , 𝐿𝑖 + , or 𝑁𝐻4+
are almost always soluble.
