CHEM 120 Final Exam | Complete Practice
QUESTIONS, Verified Answers & Detailed Rationales
(2026/2027)
QUESTION 1
What is the correct chemical formula for calcium phosphate?
• A. CaPO4
• B. Ca3 (PO4 )2
• C. Ca2 (PO4 )3
• D. Ca(PO3 )2
Correct Answer: B. Ca3 (PO4 )2
Detailed Rationale: Calcium ions typically carry a +2 charge (Ca2+ ),
while the phosphate polyatomic ion carries a −3 charge (PO3− 4 ). To
achieve electrical neutrality, three calcium ions (3 × +2 = +6) combine
with two phosphate ions (2 × −3 = −6), resulting in the formula
Ca3 (PO4 )2 .
QUESTION 2
An isotope of gallium has a mass number of 67 and an atomic number
of 31. How many neutrons does this isotope contain?
• A. 31
• B. 36
• C. 67
, • D. 98
Correct Answer: B. 36
Detailed Rationale: The number of neutrons in an atom is calculated by
subtracting the atomic number (number of protons, 𝑍 = 31) from the
mass number (𝐴 = 67). Therefore, 67 − 31 = 36 neutrons.
QUESTION 3
What is the molarity of a solution prepared by dissolving 58.5 g of
sodium chloride (NaCl) in enough water to make exactly 2.00 L of
solution? (Molar mass of NaCl = 58.44 g/mol)
• A. 0.250 M
• B. 0.500 M
• C. 1.00 M
• D. 2.00 M
Correct Answer: B. 0.500 M
Detailed Rationale: First, calculate the moles of NaCl by dividing the
mass by its molar mass: 58.5 g/58.44 g/mol ≈ 1.00 mol. Molarity (𝑀)
is defined as moles of solute divided by liters of solution: 1.00 mol/
2.00 L = 0.500 M.
QUESTION 4
If a balloon filled with helium gas is heated with a hair dryer, what will
happen to the volume of the balloon, assuming pressure remains
constant?
• A. The volume will decrease.
, • B. The volume will increase.
• C. The volume will remain unchanged.
• D. The volume will drop to zero.
Correct Answer: B. The volume will increase.
Detailed Rationale: According to Charles's Law, the volume of a given
mass of gas is directly proportional to its absolute temperature at
constant pressure (𝑉1 /𝑇1 = 𝑉2 /𝑇2 ). As heat is applied, the temperature
increases, causing the gas molecules to move faster and expand the
volume of the flexible container.
QUESTION 5
Which of the following compounds contains a peptide bond?
• A. Carbohydrate
• B. Triglyceride
• C. Protein (Polypeptide)
• D. Nucleic acid
Correct Answer: C. Protein (Polypeptide)
Detailed Rationale: Peptide bonds (amide bonds) are formed between
the carboxyl group of one amino acid and the amino group of another,
linking amino acids together to form primary protein structures.
QUESTION 6
Balance the following skeletal chemical equation: Li(𝑠) + H2 O(𝑙) →
LiOH(𝑎𝑞 ) + H2 (𝑔)
• A. Li + H2 O → LiOH + H2
, • B. 2Li + 2H2 O → 2LiOH + H2
• C. Li + 2H2 O → LiOH + 2H2
• D. 2Li + H2 O → Li2 OH + H2
Correct Answer: B. 2Li + 2H2 O → 2LiOH + H2
Detailed Rationale: Balancing chemical equations requires an equal
number of each type of atom on both sides. Placing coefficients of 2 in
front of lithium and water and a 2 in front of lithium hydroxide balances
two lithium atoms, four hydrogen atoms, and two oxygen atoms on
both sides.
QUESTION 7
What type of protein structure is characterized by alpha-helices and
beta-pleated sheets held together by hydrogen bonds along the
backbone?
• A. Primary structure
• B. Secondary structure
• C. Tertiary structure
• D. Quaternary structure
Correct Answer: B. Secondary structure
Detailed Rationale: Secondary protein structure refers to the local
folded structures that form within a polypeptide due to hydrogen
bonding between backbone carbonyl oxygen and amide hydrogen
atoms, typically resulting in alpha-helices or beta-pleated sheets.
QUESTION 8
QUESTIONS, Verified Answers & Detailed Rationales
(2026/2027)
QUESTION 1
What is the correct chemical formula for calcium phosphate?
• A. CaPO4
• B. Ca3 (PO4 )2
• C. Ca2 (PO4 )3
• D. Ca(PO3 )2
Correct Answer: B. Ca3 (PO4 )2
Detailed Rationale: Calcium ions typically carry a +2 charge (Ca2+ ),
while the phosphate polyatomic ion carries a −3 charge (PO3− 4 ). To
achieve electrical neutrality, three calcium ions (3 × +2 = +6) combine
with two phosphate ions (2 × −3 = −6), resulting in the formula
Ca3 (PO4 )2 .
QUESTION 2
An isotope of gallium has a mass number of 67 and an atomic number
of 31. How many neutrons does this isotope contain?
• A. 31
• B. 36
• C. 67
, • D. 98
Correct Answer: B. 36
Detailed Rationale: The number of neutrons in an atom is calculated by
subtracting the atomic number (number of protons, 𝑍 = 31) from the
mass number (𝐴 = 67). Therefore, 67 − 31 = 36 neutrons.
QUESTION 3
What is the molarity of a solution prepared by dissolving 58.5 g of
sodium chloride (NaCl) in enough water to make exactly 2.00 L of
solution? (Molar mass of NaCl = 58.44 g/mol)
• A. 0.250 M
• B. 0.500 M
• C. 1.00 M
• D. 2.00 M
Correct Answer: B. 0.500 M
Detailed Rationale: First, calculate the moles of NaCl by dividing the
mass by its molar mass: 58.5 g/58.44 g/mol ≈ 1.00 mol. Molarity (𝑀)
is defined as moles of solute divided by liters of solution: 1.00 mol/
2.00 L = 0.500 M.
QUESTION 4
If a balloon filled with helium gas is heated with a hair dryer, what will
happen to the volume of the balloon, assuming pressure remains
constant?
• A. The volume will decrease.
, • B. The volume will increase.
• C. The volume will remain unchanged.
• D. The volume will drop to zero.
Correct Answer: B. The volume will increase.
Detailed Rationale: According to Charles's Law, the volume of a given
mass of gas is directly proportional to its absolute temperature at
constant pressure (𝑉1 /𝑇1 = 𝑉2 /𝑇2 ). As heat is applied, the temperature
increases, causing the gas molecules to move faster and expand the
volume of the flexible container.
QUESTION 5
Which of the following compounds contains a peptide bond?
• A. Carbohydrate
• B. Triglyceride
• C. Protein (Polypeptide)
• D. Nucleic acid
Correct Answer: C. Protein (Polypeptide)
Detailed Rationale: Peptide bonds (amide bonds) are formed between
the carboxyl group of one amino acid and the amino group of another,
linking amino acids together to form primary protein structures.
QUESTION 6
Balance the following skeletal chemical equation: Li(𝑠) + H2 O(𝑙) →
LiOH(𝑎𝑞 ) + H2 (𝑔)
• A. Li + H2 O → LiOH + H2
, • B. 2Li + 2H2 O → 2LiOH + H2
• C. Li + 2H2 O → LiOH + 2H2
• D. 2Li + H2 O → Li2 OH + H2
Correct Answer: B. 2Li + 2H2 O → 2LiOH + H2
Detailed Rationale: Balancing chemical equations requires an equal
number of each type of atom on both sides. Placing coefficients of 2 in
front of lithium and water and a 2 in front of lithium hydroxide balances
two lithium atoms, four hydrogen atoms, and two oxygen atoms on
both sides.
QUESTION 7
What type of protein structure is characterized by alpha-helices and
beta-pleated sheets held together by hydrogen bonds along the
backbone?
• A. Primary structure
• B. Secondary structure
• C. Tertiary structure
• D. Quaternary structure
Correct Answer: B. Secondary structure
Detailed Rationale: Secondary protein structure refers to the local
folded structures that form within a polypeptide due to hydrogen
bonding between backbone carbonyl oxygen and amide hydrogen
atoms, typically resulting in alpha-helices or beta-pleated sheets.
QUESTION 8
